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MARYLAND

GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN

BALTIMORE

THE JOHNS HOPKINS PRESS IQIQ

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JSorft (gaftttnore (preee

BALTIMORE, MD., U. 8. A.

SCIENCES

COMMISSION

EMERSON C. HARRINGTON, . . . . . PBESIDENT.

GOVERNOR OF MARYLAND.

HUGH A. McMULLEN, . . . . . . . . i

COMPTROLLER OF MARYLAND.

FRANK J. GOODNOW, . . . EXECUTIVE OFFICEE.

PRESIDENT OF THE JOHNS HOPKINS UNIVERSITY.

A. F. WOODS, . . SECEETAEY.

PRESIDENT OF THE STATE COLLEGE OF AGRICULTURE.

416455

SCIENTIFIC STAFF

EDWARD BENNETT MATHEWS, .... STATE GEOLOGIST. SUPERINTENDENT OF THE SURVEY

EDWARD W. BERRY, . . . ASSISTANT STATE GEOLOGIST.

CHARLES K. SWARTZ, GEOLOGIST.

J. T. SINGEWALD, JR., ' GEOLOGIST.

EUGENE H. SAPP, . . . .... . ASSISTANT.

Miss MYRA ALE, SECRETARY.

LETTER OF TRANSMITTAL

To His Excellency EMEKSON C. HARRINGTON,

Governor of Maryland and President of the Geological Survey Com- mission,

Sir: — I have the honor to present herewith the seventh of a series of reports dealing with the systematic geology and paleontology of Maryland. The preceding reports of this series have dealt with the Devonian, Lower Cretaceous, Upper Cretaceous, Eocene, Miocene, and Plio-Pleistocene deposits and the remains of animal and plant life which they contain. The present volume treats of the Cambrian and Ordovician deposits and their contained life. These rocks comprise the oldest fossiliferous rocks of the state, a knowledge of which is extremely important from a scientific, educational, and economic standpoint. I am,

Very respectfully,

EDWARD BENNETT MATHEWS,

State Geologist. JOHNS HOPKINS UNIVERSITY,

BALTIMORE, September, 1919.

PAGB

PREFACE 19

THE CAMBRIAN AND ORDOVICIAN DEPOSITS OP MARYLAND. BY

R. S. BASSLEB 21

INTRODUCTION 23

THE PHYSIOGRAPHY 23

THE GEOLOGY 24

HISTORICAL REVIEW 25

BIBLIOGRAPHY 34

PALEOGEOGRAPHY OF THE CAMBRIAN AND ORDOVICIAN 45

STRATIGRAPHIC AND PALEONTOLOGIC CHARACTERISTICS 50

CAMBRIAN SILICEOUS FORMATIONS 52

The London Formation 53

The Weverton Sandstone 54

The Harpers Shale 57

The Antietam Sandstone 58

CAMBRIAN-ORDOVICIAN LIMESTONES 60

The Tomstown Limestone 61

Topography 61

Lithologic Characters 62

Residual Products 63

Economic Features 64

Areal Distribution 65

Thickness 66

Age and Correlation 66

The Waynesboro Formation 66

Name and Synonymy 67

Lithologic Character and Thickness 68

Topographic Form 69

Tomstown — Waynesboro Boundary 69

Areal Distribution 70

Economic Features V 1

Age and Correlation 71

The ElbrooTc Formation 72

Lithologic Character and Thickness 72

Areal Distribution 72

Topographic Form and Residual Products 73

Age and Correlation 74

The Conococheague Limestone 74

Lithologic Character and Thickness 76

Topography • 81

Areal Distribution 81

Age and Correlation 82

Cryptozoon Reefs 83

Edgewise Conglomerate 86

CONTENTS

PAGE

Fossils of Cambrian Age 88

The Beekmantown Limestone 89

Lithologic Character 92

Faunal Zones 96

Stonehenge Member 96

Cryptozoon steeli Zone 101

Ceratopea Zone 103

Turritoma Zone 104

Topography and Residual Products 105

Areal Distribution 109

Frederick Valley Limestones Ill

The Beekmantown Limestone 114

The Frederick Limestone 115

The Stones River Limestone 117

General Sections 117

Lithologic Character 121

Paleontology 121

Lower Stones River 122

Middle Stones River 124

Upper Stones River 126

Areal Distribution and Topographic Features 126

Fauna of the Stones River in Maryland 127

The Chambersburg Limestone 129

Lithologic Character 130

Areal Distribution 132

Faunal Zones 132

Caryocystites Bed 133

Tetradium cellulosum Bed 136

Echinospherites Bed 139

Nidulites Bed 140

Christiania Bed 142

Greencastle Bed 143

Sections of the Chambersburg Limestone 144

East of Martinsburg Shale Belt 144

West of Martinsburg Shale Belt 147

Variations in Distribution 152

Age and Correlation 153

UPPER OEDOVICIAN SHALES 134

The Martinsburg Shale 154

Lithologic Character and Sections 157

Topographic Features and Areal Distribution 161

Faunas 163

Sinuites Bed of Trenton Age 163

Corynoides Bed of Trenton Age 165

Eden Division 167

Maysville Sandstone Division 168

The Juniata Formation 170

TABLES SHOWING DISTRIBUTION OF SPECIES 174

CONTENTS 13

PAGE

SYSTEMATIC PALEONTOLOGY, CAMBRIAN AND ORDOVICIAN 187

THALLOPHYTA, R. S. BASSLER 189

PoRiFERA, R. S. BASSLER 195

COELENTERATA, R. S. BASSLER 198

ECHINODERMATA, R. S. BASSLER 207

MOLLTJSCOIDEA, R. S. BASSLER 212

VERMES, R. S. BASSLER 276

MOLLUSCA, R. S. BASSLER 277

ARTHROPODA, R. S. BASSLER 332

GENERAL INDEX 409

PALEONTOLOGICAL INDEX .417

ILLUSTRATIONS

PLATE FACING PAQB

I. Map showing the Distribution of the Cambrian and Ordovician

Deposits of Maryland , . 23

II. View of the Potomac Water Gap at Harper's Ferry 52

III. Fig. 1. — View of the Great Valley from South Mountain at Blue

Mountain Station 56

Fig. 2. — View along road between Pen Mar and High Rock, Mary- land, showing mountain side covered with blocks of Weverton quartzite 56

IV. Fig. 1. — Exposure of Tomstown limestone along trolley line just

southeast of Wagner's Cross Road, Washington County, Mary- land, illustrating weathering of massive sheared limestone into shale fragments 62

Fig. 2. — Limestone quarry at Cavetown, Maryland, showing Toms- town limestone faulted against Waynesboro sandstone 62

V. Fig. 1. — Valley of Tomstown limestone looking east from Cave- town, Maryland, showing foothills of Harpers shale, and South Mountain of Weverton sandstone in the distance 64

Fig. 2. — Valley of Tomstown limestone with South Mountain in the distance showing peneplained surface. The hill just beyond the house is capped by Tomstown chert. Photograph

taken one mile south of Cavetown, Maryland 64

VI. Fig. 1. — Overturned fold with slight faulting in Tomstown lime- stone along Western Maryland Railway, one mile west of Cavetown, Maryland 66

Fig. 2. — Ridge of the Waynesboro formation just east of Middle

Bridge, Antietam Battlefield, Washington County, Maryland . . 66 VII. Iron stained contorted sandstone of Waynesboro formation. The upper figure represents the usual aspect of the rock. The cavities in the sandstone are covered by drusy quartz as shown in the figure to the left (x2) or by beautiful minute

crystals of quartz illustrated in figure to right (x 6) 68

VIII. Fig. 1. — Exposure of Elbrook limestone along Baltimore and Ohio Railroad just south of Sharman, Maryland. These massive beds weather into thin shaly layers 72

Fig. 2. — View looking north over Antietam Battlefield showing exposure of Elbrook limestone. Photograph taken one-half mile east of Sharpsburg, along road to Burnside Bridge, Maryland 72

16

ILLUSTRATIONS

PLATE FACING PAGE

IX. Fig. 1. — Cryptozoon reef at base of Conococheague formation, ex- posed along Norfolk and Western Railroad about one mile southwest of Antietam Station, Maryland. Photograph about one-fifteenth natural size 76

Fig. 2. — Cryptozoon structure in upper part of Conococheague limestone exposed along Western Maryland Railway, one- quarter mile west of Charlton, Maryland. Photograph one- sixth natural size 76

X. Fig. 1. — Exposure of Conococheague limestone on edge, along road near Bakersville, Maryland. The characteristic strongly crinkled, sandy laminae are well developed 80

Fig. 2. — Lower Conococheague scoriaceous chert exposed in fence along Hagerstown turnpike just north of Sharpsburg, Mary- land 80

XI. " Edgewise beds " characteristic of Beekmantown and Conoco- cheague formations, Hagerstown Valley, Washington County. 82 XII. Fig. 1. — Quarry in upper part of Conococheague limestone with

Security Cement Works, Security, Maryland, in distance. ... 84

Fig. 2. — Typical exposure of the lower pure finely conglomeratic beds of the Stonehenge limestone along National Highway, just south of Funkstown, Maryland 84

XIII. Fig. 1. — Exposure of steeply inclined Stonehenge limestone

(upper division) at Charlton, Maryland, showing the dis- integration into siliceous shale, upon prolonged weathering. . . 96 Fig. 2. — Typical exposure of edgewise conglomerate from the upper part of the Stonehenge limestone, Baltimore and Ohio Railroad, one mile north of Balls, Maryland 96

XIV. Fig. 1. — View of a weathered outcrop of the upper Stonehenge

limestone, eastern edge of Hagerstown, Maryland 100

Fig. 2. — View taken from hill of upper Stonehenge limestone, eastern edge of Hagerstown, Maryland, looking east, showing effect of weathering of the various formations upon topog- raphy 100

XV. Fig. 1. — Exposure of lower Beekmantown limestone just above the Stonehenge member in brickyard, eastern edge of Hagers- town, Maryland. Clay for brick manufacture results from the

weathering of the purer beds 104

Fig. 2. — Beekmantown limestone at LeGore quarry, LeGore, Mary- land. The weathered outcrops of these strata have yielded

numerous cephalopods 104

XVI. Fig. 1. — Near view of Beekmantown limestone at LeGore quarry, LeGore, Maryland. Strata penetrated by a six-inch diabase

dyke (marked by hammer) 108

Fig. 2. — View of contact between the Beekmantown (B) and Stones River (S) limestone along the south side of the National Highway at Wilson, Maryland. The zone of cauli- flower chert (C) is well displayed at this place 108

ILLUSTRATIONS 17

PLATE FACING PAGE

XVII. Fig. 1. — An average example of the cauliflower chert from the base of the Stones River limestone. Vicinity of Bostetter, Maryland 120

Fig. 2. — Typical natural outcrop of upper Stones River limestone in cleared fields, one-half mile west of Pinesburg, Maryland. The growth of cedar trees on this pure limestone is illustrated. 120 XVIII. Fig. 1. — View of edgewise conglomerate in Stones River forma- tion, two and one-half miles southeast of Williamsport, Mary- land 122

Fig. 1. — View of quarry in Chambersburg limestone at Pinesburg

Station, Maryland 122

XIX. Fig. 1. — Photograph showing succession of sinks along the band of outcrop of the Stones River limestone, one-half mile south of Wilson, Maryland. The road to the east follows the Cham- bersburg limestone 126

Fig. 2. — Near view of a sink filled with water 126

XX. Fig. 1. — Typical exposure of the Echinospherites bed of the Cham- bersburg limestone showing characteristic cobbly effect. Rail- road cut at Pinesburg Station, Maryland 130

Fig. 2. — Typical outcrop of steeply dipping Chambersburg lime- stone along road between Pinesburg and Pinesburg Station,

Maryland 130

XXI. Fig. 1. — View in the Tabler quarry just south of Frederick, Mary- land, showing contact of the massive Beekmantown limestone overlaid by the thin-bedded Frederick limestone with a dis- tinct line of unconformity separating them 160

Fig. 2. — Fold in sandy upper (Eden) portion of Martinsburg shale along Western Maryland Railway, three-fourths mile

west of Williamsport, Maryland 160

XXII. Fig. 1. — Exposure of lower part of Martinsburg shale along Western Maryland Railway, about one-half mile east of Pines- burg Station, Maryland. The gentle dip of the strata and the cleavage at right angles are well shown 104

Fig. 2. — View across valley of Conococheague and Beekmantown limestones, from a point two miles east of Little Georgetown, West Virginia. Conococheague chert strews the foreground. North Mountain in the distance contains the Juniata and

Tuscarora formations 164

XXIII. Fig. 1. — View of Martinsburg shale topography, looking northeast from a point one-half mile south of Wilson, Maryland. Cono- cocheague Creek is seen in the foreground and the National Highway in the middle 170

Fig. 2.— Valley of Martinsburg shale (Blair Valley, Maryland) viewed from road, just west of Union Bethel Church. The mountains on both sides are formed of the Juniata and Tus- carora formations 170

XXIV to LVI1I. Systematic Paleontology 374-408

18 ILLUSTRATIONS

FIGURE PAGE

1. Columnar section of the Cambrian, Ozarkian, and Canadian strata of

Maryland 48

2. Columnar section of the Ordovician rocks of Maryland 49

3. Cambrian-Ordovician Correlation Table 51

4. Paleogeographic map of Lower Cambrian (Waucoban) 55

5. Paleogeographic map of Middle Cambrian (Acadian) 55

6. Paleogeographic map of Upper Cambrian (St. Croixan) 75

7. Paleogeographic map of Early Ozarkian (Conococheague) 75

8. Paleogeographic map of Upper Ozarkian (Copper Ridge) 79

9. Paleogeographic map of Late Ozarkian (Chepultepec) 79

10. Paleogeographic map of Lower Canadian (Bretonian) 91

11. Paleogeographic map of Middle and Late Canadian (Beekmantown) . 91

12. Structure Sections across Frederick Valley 112

13. Paleogeographic map of Early Ordovician (St. Peter) 119

14. Paleogeographic maps of Early Ordovician (Mosheim) 119

15. Paleogeographic map of Early Ordovician (Middle Stones River)

Maclurites magnus fauna 125

16. Paleogeographic map of Early Ordovician (Upper Stones River) 125

17. Diagrammatic section of Chambersburg limestone from Chambers-

burg, Pa., to Strasburg, W. Va 131

18. Paleogeographic map of Early Ordovician (Blount) 134

19. Paleogeographic map of Middle Ordovician. Lower Black River

(Lowville) 134

20. Paleogeographic map of Middle Ordovician. Middle Black River

(Decorah) 138

21. Paleogeographic map of Middle Ordovician. Upper Black River

(Kimmswick) 138

22. Paleogeographic map of Middle Ordovician. (Latest Chambersburg) . 155

23. Paleogeographic map of Middle Ordovician (Early Trenton) 155

24. Paleogeographic map of Late Ordovician. Early Cincinnatian

(Utica) 159

25. Paleogeographic map of Late Ordovician. Cincinnatian (Eden) 159

26. Paleogeographic map of Late Ordovician. Cincinnatian (Fairview) . 162

27. Paleogeographic map of Late Ordovician. Cincinnatian (Oswego or

McMillan) 162

PREFACE

The present volume is the seventh of a series of reports dealing with the systematic geology and paleontology of Maryland, the Devonian, Lower Cretaceous, Upper Cretaceous, Eocene, Miocene and Plio-Pleisto- cene deposits having already been fully described.

This volume is devoted to a consideration of .the Cambrian and Ordo- vician deposits and their contained faunas. The calcareous strata making up a considerable part of these two systems are so intimately united in the Appalachians that they have long remained unseparated under the name Cambro-Ordovician limestone, or, as in Maryland and Virginia, the Shenandoah limestone. It was therefore thought eminently fitting to combine their consideration in one volume and to disregard in the title the Ozarkian, the Canadian, and other possible systems which have been suggested in recent years.

Upon the completion of studies on the Cambrian and Ordovician rocks of Virginia in 1909, published as Bulletin 2 A of the Virginia Geological Survey under the title " Cement Resources of Virginia west of the Blue Ridge," the writer, upon the invitation of the late Dr. William Bullock Clark, undertook the preparation of the Maryland volume dealing with the systematic geology and paleontology of the Cambrian and Ordovician systems. As this work included the mapping of these strata in areas both west and east of the Blue Ridge, and as only a few weeks were available each summer for the necessary field work, the volume has been long delayed. However, this delay has proved fortunate, for during the interval of its preparation the knowledge of Cambrian and Ordovician stratigraphy has progressed so much that it is hoped fewer mistakes will now be recorded.

During the preparation of the Mercersburg-Chambersburg folio descrip- tive of the region in Pennsylvania, just north of the Maryland state line,

20 PREFACE

the writer had the advantage of association with E. 0. Ulrich and George W. Stose in their studies of the stratigraphy and paleontology of that area. He thus helped to collect the data and became acquainted with the Cambrian and Ordovician faunas and sections which are so well displayed there, but not as well developed in Maryland.

Dr. Richard C. Williams, while a graduate student at Johns Hopkins University, assisted in the mapping of the Cambrian and Ordovician strata, especially in the Hagerstown area. The Maryland Geological Survey has also had the cooperation of the IT. S. Geological Survey, Mr. George W. Stose of that organization being associated in the field work in the Williamsport quadrangle in the area west of the Martinsburg shale belt.

The Survey is also indebted to Dr. E. 0. Ulrich of the U. S. Geological Survey for permission to incorporate in this volume a set of his paleo- geographic maps covering the Cambrian and Ordovician formations.

THE CAMBRIAN AND ORDOVICIAN DEPOSITS OE MARYLAND

MARYLAND GEOLOGICAL SURVEY

MAP

SHOWING THE DISTRIBUTION OF THE

CAMBRIAN AND ORDOVICIAN FORMATIONS

OF

MARYLAND

BY K. 8. BAS8LER

1919

LEGEND

Of ! Frederick limestone

Om Martiuslmrtf shale

MARYLAND GEOLOGICAL SURVEY EDWARD BENNETT MATHEWS. STATE GEOLOGIST

SCAI.K : One inch equals five miles 1:312,500

Cc

Conococheague limestone

Ce Klbrook limestone

• Waynesboro formation Ct I Tomstown limestone

Silurian and Devi Pre Cambrian coi

„,] Antietam, Harpers, Weverton and Loudon

WOO

Beekmantowu limestone Newark formation

77°50'

77° 40'

CAMBRIAN— ORDOVICIAN PLATE I

77°io'

77°20'

THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

BY R. S. BASSLER

INTRODUCTION

The Cambrian and Ordovician deposits of Maryland can only be interpreted through an understanding of the geology of the extensive province extending from eastern Canada to Alabama, of which the State of Maryland forms a part. The Cambrian and Ordovician formations of Maryland extend far beyond the confines of the state and in adjacent areas to the north or south frequently afford more satisfactory evidence of their character and fossil content than they do in Maryland.

THE PHYSIOGEAPHY

The region here considered forms a small portion of the Atlantic slope, which stretches from the crest of the Alleghanies to the sea, and which is divided into three more or less sharply defined physiographic regions known as the Appalachian Region, the Piedmont Plateau, and the Coastal Plain. These three districts follow the Atlantic border of the United States in three belts of varying width from New England southwestward to the Gulf states.

The Appalachian Region extends from beyond the western limits of the state eastward to the Blue Ridge and is divided into three districts known as the Alleghany Plateau, the Greater Appalachian Valley, and the Blue Ridge District. The first is west of the Alleghany Front and contains rocks younger than Ordovician. Extending along the eastern border of the Alleghany Front is the district known as the Greater Appalachian Valley which admits of a twofold division into the zone of Alleghany

24 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

Eidges on the west and the Great Valley on the east, the latter known as the Hagerstown Valley in Maryland, the Cumberland Valley in Pennsyl- vania, and the Shenandoah Valley in Virginia. The Great Valley is a broad lowland with an elevation averaging between 500 and 600 feet and gradually increasing in height to the northward. It extends from New York state to Alabama and in Maryland lies between North Mountain on the west and the Blue Eidge on the east. The Blue Eidge district con- sists of the Blue Eidge and Catoctin mountains which unite immediately north of the Maryland-Pennsylvania boundary to form the greater high- land known as South Mountain.

The Piedmont Plateau borders the Blue Eidge district on the east and comprises the hill country of ancient rocks lying between the Blue Eidge on the west and the Coastal Plain district on the east — the latter district sloping gradually to the southeast and becoming submerged beneath the Atlantic. The Piedmont Plateau is divided into an Eastern Division and a Western Division by the upland known as Parr's Eidge which forms the low divide at an average elevation of between 800 and 900 feet of the streams flowing directly into Chesapeake Bay and those flowing into Potomac Eiver. The Western Division in Maryland corresponds rather closely to what is known as the Frederick Valley.

THE GEOLOGY

The Cambrian and Ordovician formations in Maryland are confined to the eastern division of the Appalachian Eegion, previously described as the Great Valley and Blue Eidge, and to the western division of the Piedmont Plateau Eegion.

The Cambrian formations consist of shales, limestones, and sandstones of sedimentary origin which have been subjected to much metamorphism and marked structural disturbances since they were deposited. They cover considerable areas in Washington and Frederick counties. The Ordovician formations are found in association with the Cambrian in the Great Valley and Blue Eidge regions and also in the Frederick Valley. The Ordovician sediments have been much folded and faulted, but they are, on the whole, less metamorphosed than those of Cambrian age.

MARYLAND GEOLOGICAL SURVEY 25

HISTOKICAL EEVIEW

It will be remembered that previous to 1830 geologists grouped into a single large and indefinite " Transition Series " all of the sedimentary and interbedded volcanic rocks of Great Britain older than the Car- boniferous. Immediately underlying the Carboniferous was the great mass of red sandstones and marls first designated the Old Eed sandstone and later determined as of Devonian age. In 1831, Sir Eoderick I. Murchison and Professor Adam Sedgwick attacked the problem of the division of the remaining underlying strata, confining their studies to the rocks of western England and eastern and southeastern Wales. Murchison undertook this study under favorable circumstances, as he began his researches at the upper end of the series where fossils abound and the structure is simple. He found that the different members of the upper part of this great series could be recognized by the fossils as easily as more recent strata, and he continued to discover fossiliferous zones lower and lower in the series. He first designated these strata as the "fossiliferous graywacke series," but in 1835 he changed this to the " Silurian System," named after the Silures, a tribe of ancient Britons. Sedgwick, on the other hand, attempted the division of the transition series in the Snowdon district of Wales where the complicated structure and highly altered nature of the rocks, and consequent scarcity of fossils, made the problem an extremely difficult one. In 1835 he proposed the name " Cambrian Series " for the lower, older member, taking the name from Cambria, the Roman name for northern Wales.

Murchison divided his Silurian system into an upper and lower portion which were separated from each other, as pointed out by Sedgwick, by an angular unconformity marking the boundary between the Caradoc and the Llandovery groups. The lower limit of his Silurian was not defined, but he finally included all of the fossiliferous strata of Sedgwick's Cambrian.

Murchison. in his volume on the Silurian system published in 1839, recognized the Cambrian series, and up to this point the two workers agreed. However, in 1842, in his presidential address to the Geological Society of London, he stated that the Cambrian fossils did not differ from

26 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

those of the Lower Silurian, an opinion eminently correct because, as just noted, he had included in it all of the fossiliferous Cambrian. In the publication of his Siluria several years later, Murchison still regarded Sedgwick's Cambrian system as simply a local facies of the Silurian system. The historic but unfortunate controversy on this question now ensued. Murchison, by means of his influential official and social position, was able to dominate the subject and most of the rocks now recognized as Cambrian, Ordovician, and Silurian were marked Silurian on the British geological maps, and in both America and Europe fossils collected from the equivalent of the " Transition Series " were almost invariably classed as Silurian. The term Cambrian was practically discarded because, according to Murchison, it was impossible to recognize the strata on account of their supposed lack of characteristic fossils.

Tn 1879 Professor Lapworth of Birmingham University, England, proposed that Murchison's term Lower Silurian be replaced by the name Ordovician, after the Ordovices, a tribe which lived in Wales at the time of the Romans. Sedgwick in his writings continued to insist that the Cambrian system was an independent group of rocks and proposed to limit the Silurian to the Ludlow and the Wenlock, with the Mayhill sand- stone at the base. In his introduction to Salter's Catalogue of Cambrian and Silurian fossils, published in 1873, the year of his death, he held to this same view. As practically all of the faunas which he" considered as Cambrian and the main mass of the rocks included by him in the Cam- brian system are now recognized as typical Ordovician, it is evident that the present-day usage of the term Cambrian does not follow the intentions of its author. The upper, typical portion of the Silurian system, to which the name Silurian was restricted when Lapworth introduced the new name Ordovician for the Lower Silurian, was named Murchisonian by d'Orbigny in 1850, but this term never received a wide acceptance.

With the adoption of the terms Ordovician and Silurian by many geologists the name Cambrian was finally retained for the lower, much more sparingly, unfossiliferous rocks of the original Cambrian of Sedg- wick— a most unfair procedure and one to which that author objected

MARYLAND GEOLOGICAL SURVEY 27

vigorously in his lifetime. Still another classification of pre-Devonian Paleozoic rocks is that of De Lapparent who recognized the Silurian for the entire interval, with the three divisions — ;Cambrian, Ordovician, and Bohemian or Gothlandian.

Another term which enters into this controversy is that of the Taconic system. The Taconic question was the basis of a controversy in America similar to that of the Silurian in Great Britain. In 1838 Emmons noted that the Potsdam sandstone was the oldest sedimentary rock in the vicinity of Potsdam, New York, as it here rested upon pre-Paleozoie crystallines, an observation still recognized as correct. Overlying the Potsdam sandstone, he found the Calciferous sandrock, the Chazy, Birds- eye, and Trenton limestones, and the Utica and Hudson Kiver shales. In western Massachusetts at the foot of the Hoosac Mountains he found an entirely different series resting directly upon the gneiss. Emmons believed this series to be older than the Potsdam and in 1841 he applied to it the name Taconic system, after the Taconic range. The controversy which arose over the reality of his system lasted over half a century, and although Emmons defended his opinion until the day of his death, stratigraphic geology had then not proceeded far enough to recognize the real value of the Taconic rocks in classification. It is now known that the greater portion of the Taconic is of Cambrian age. With slight emendations the term Taconic could in all fairness have been recognized for the Cambrian or for a portion of it just as Sedgwick's term Cambrian should have been applied to the rocks now called Ordovician.

During the quarter of a century or more following Lapworth's defini- tion of the Ordovician system and the recognition in America of the Cambrian, Ordovician, and Silurian, with the limits generally accepted to-day, no controversial matters of especial importance arose in Early Paleozoic stratigraphy. Most students of the subject believed that Early Paleozoic sedimentation took place in quiet continental seas which were often of considerable depth. It was thought that sedimentation endured without interruption either through a single period or sometimes through several periods, until finally there was land elevation and withdrawal of

28 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND

the sea. Then after extensive erosion, the sinking of the land and incur- sion of the sea inaugurated another period of geological history. Faunal differences in apparently contemporaneous strata were attributed to the different habitats of the organisms, while the absence of certain strata over wide areas was explained by the erosion during the land interval. The great changes in lithological character from place to place depended upon the topography of the land masses bordering the continental seas.

In the last decade so many new stratigraphic and paleontologic facts have come to light that the old conceptions regarding stratigraphic corre- lation and the ideas concerning the character and extent of the ancient continental seas have been greatly modified and .often discredited. The lifelong studies of E. 0. Ulrich upon the stratigraphy and paleontology of the American Paleozoic have brought to light new criteria for systemic delimitation, and caused him to propose a revision of the Paleozoic sys- tems based upon these new conceptions. According to his views there never was a vast continental sea of considerable depth enduring through any great period of deposition, nor was there ever any considerable elevation of the adjacent land masses with the consequent erosion, except for compara- tively brief periods. In his work in collaboration with Professor Charles Schuchert, published in Bulletin 52 of the New York State Museum under the title " Paleozoic seas and barriers in eastern North America/' it was brought out that the diastrophic movements producing deformation of the land masses, manifested themselves not only between the larger divisions of geologic time, but even between formations. These move- ments resulted in a north and south warping of the continent with the formation of narrow structural troughs whose position was determined by their location in areas with a predisposition to sink. These troughs or negative areas were separated more or less completely by anticlinal areas which had a positive tendency to remain above sea level in all except the periods of most general submergence.

These positive and negative areas were discussed in more detail by Schuchert in his great work on the Paleogeography of North America, published in 1910 in the Bulletin of the Geological Society of America.

29

The positive areas were seldom elevated enough to have great erosive activity and the land masses were generally quite low. As a result there are certain limestone formations which hold their lithologic character for hundreds of miles.

In his epoch-making work on the Eevision of the Paleozoic Systems, published in volume 22 of the Bulletin of the Geological Society of America, in 1911, Ulrich has given a very detailed account of the dia- strophic and faunal criteria employed by him in his studies on strati- graphic classification, and he has devoted much attention to the oscillatory character of continental seas. The northeast-southwest troughs, separated by barriers or areas around which warping took place, were invaded by the sea many times during the course of a period. Other barriers or areas extending at approximate right angles to these troughs, separated them into basins. The general idea was that the sea advanced and retreated many times during the course of a period within these comparatively restricted basins. With each successive invasion sediments were deposited over a larger area so that the final result was a series of overlapping deposits thinning out on the sides of the trough. Each trough or basin would contain series of formations marked off by diastrophic and faunal evidence and a formation would be lithologically and f aunally similar only in its own basin, except in periods of great submergence when the sea advanced over the barriers. As the different basins of sedimentation at times connected with different oceanic areas, the marine forms of life in them would consequently be different. Therefore, formations of the same age in adjoining basins may differ totally not only in their lithologic characters, but also in their faunal contents. These troughs of deposition, with their separating barriers, were greatly influenced by later and later periods of diastrophism with the result that in the Appalachians, where folding occurred, the barrier or anticlinal structure is now much dimin- ished in width and is often represented by an overthrust fault.

In addition to the north and south structural lines it has been found that there were definite east and west lines or axes which serve as pivots of oscillation for the continent. The formations thin from either side

30 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

along these lines just as in the north and south structural troughs they thin along the edges of the trough.

The greatest sea withdrawal marks the systemic boundaries, but the advance and retreat of the seas within the systems would naturally not be uniform throughout the basins of deposition. Therefore one area will have deposits which are represented in another area by a stratigraphic hiatus. As a result of this, the complete section cannot be found at any one place but it is a composite one made up of units from many places. The disregard of this fact has delayed the recognition of many new formations heretofore, as in the case of the so-called Ozarkian.

Under the conception of little elevation and often slight erosion of the Eopaleozoic land masses, the stratigraphic unconformities are not strongly marked even though the time interval may have been great. The bedding planes of strata belonging to distinct formations are usually parallel and the detection of such unconformities is most difficult. The f aunal method of discrimination is a sure one, provided the occurrence and range of the faunas are well known. Another method is in the comparison of detached sections and noting the gradual interpolation of other strata between two formations with persistent lithologic characters. In the discrimination of the Ordovician rocks of Maryland, this latter method is extremely useful, as several of the formations developed in states to the north and south are represented here only by their overlapping margins.

In the classification of Paleozoic rocks, as commonly recognized, the Cambrian and Ordovician systems forming the subject of this volume comprise the Eopaleozoic. In his revision of the Paleozoic systems, Ulrich has proposed and defined two new systems, the Ozarkian and Canadian, which occupy the interval between a slightly restricted Cambrian and a more modified Ordovician system. Brief descriptions of these new systems were read at the Baltimore meeting of the Geological Society of America in 1909, but were not published until 1911. In 1910, in his Paleogeography of North America, Schuchert adopted both of the new systems, crediting them to Ulrich, and introduced a third for the Cin- cinnatian rocks hitherto classified at the top of the Ordovician. The

MARYLAND GEOLOGICAL SURVEY . 31

principles upon which the Ozarkian and Canadian have been founded are discussed in great detail in the Eevision and their author has a mono- graphic study on their paleontology and stratigraphy in the course of preparation. Although each of the new systems (Ozarkian and Cana- dian ) contains strata heretofore in the one case referred to the underlying Cambrian and in the other to the overlying Ordovician, much the greater part of each system is composed of thick formations whose actual dis- tinctness from the typical Cambrian and Ordovician has never been appreciated. In short these two systems, like the Cambrian, Ordovician and all well-founded geologic systems, are based on a certain sequence of diastrophic events and a sufficient thickness of marine deposits to repre- sent a period of geologic time approximating in length that represented by such other well-established systems as the Silurian and Devonian. They were not founded primarily on fossil evidence, but on the physical criteria of great series of marine deposits found wedging in between the under- lying uneven top of older formations, which contain the now well-known and altogether characteristic Upper Cambrian fauna, and the similarly uneven base of another system that comprises the bulk and most char- acteristic parts of the Ordovician system of the literature. The fossil contents of the two new systems were, of course, immediately utilized in recognizing the several formations from place to place. But the Ozarkian and the Canadian faunas as such could be appreciated only after the systems themselves had been discriminated by physical criteria. So far as these faunas have been worked out they are clearly distinguishable and as different from each other and from the preceding Cambrian and the succeeding Ordovician faunas as are the organic remains in any succeed- ing contiguous pair of. systems. In other words the Ozarkian fauna as shown in Ulrich's collections in the U. S. National Museum is more radically different from the life of the Upper Cambrian seas than is the Silurian from the Ordovician, the Devonian from the Silurian, or the1 Mississippian from the Devonian. The most striking feature of the difference between the Ozarkian and the Cambrian is the strong develop- ment of straight and curved cephalopods, and numerous coiled gastro- 3

32 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

pods — types which, up to the present, are entirely absent in Cambrian faunas. The Canadian faunas introduce a wealth of graptolites, true orthoids as distinguished from Billingsellidae brachiopods, the first ostracods, and the first of the coiled cephalopods. The Ordovician fauna is at once distinguished from the Canadian by the first appearance of pelecypods, the first of the unquestionable bryozoans. and the first true crinoids.

The following table is introduced to illustrate graphically the various usages of the Silurian and related terms concerned in this volume :

Although the list of papers dealing with the geology of the parts of Maryland concerned in this volume is quite lengthy, the number of students whose observations have advanced the knowledge of the strati- graphy and paleontology of the region is comparatively small.

In 1885, Mr. H. R. Geiger began the study of the Paleozoic rocks along the Potomac River in western Maryland and West Virginia and in 1886 and 1887 extended his work eastward down the Potomac River and for some distance southward over the Great Valley region of Virginia. In 1888 he began work on the Harper's Ferry quadrangle and after several months study came to certain conclusions regarding the relations of the sandstones and associated formations in the Blue Ridge and South Mountain to the limestones of the Great Valley which are not held to-day.

In 1890 Mr. Arthur Keith undertook a reexamination of the Harper's Ferry quadrangle and as a preliminary result of his studies read a paper in joint authorship with Mr. H. R. Geiger, before the Geological Society of America on " The Structure of the Blue Ridge near Harper's Ferry." 1 The next year he published a short notice on " The Geologic Structure of the Blue Ridge in Maryland and Virginia," * and his final results appeared in the Harper's Ferry folio No. 10, Geologic Atlas of the United States.

In 1892 Mr. Charles D. Walcott made an examination of the Blue Ridge and South Mountain region and definitely determined the Cam- brian age of its quartzites. A statement of the results of this investigation

1 Bull. Geol. Soc. America, vol. ii, 1891, pp. 155-164, pis. iv, v. 3 American Geologist, vol. x, 1892, pp. 362-368.

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34 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

was set forth in two papers, one entitled " Notes on the Cambrian Bocks of Pennsylvania and Maryland from the Susquehanna to the Potomac," * and the other " The Geologist at Blue Mountain, Maryland." 2

Mr. Keith continued his studies of South Mountain and Blue Kidgc geology into Virginia and in 1894 published a report on the " Geology of the Catoctin Belt."' This report describes the Blue Eidge, South Mountain, and Catoctin belts -from northern Virginia through Maryland into Pennsylvania and was an important addition to the geologic knowl- edge of this area east of the Great Valley.

The discovery of fossils in the Frederick Valley limestone was an- nounced by Charles R. Keyes in 1890 4 in an article in which he included a geologic section across the valley. The next contribution in which fossils were mentioned was by Charles S. Prosser in 1900,5 who described the Shenandoah limestone and Martinsburg shale in a general way.

The most important contributions to the early Paleozoic stratigraphy of this region appeared in 1910 in the description of the Mercersburg-- Chambersburg district of Pennsylvania by George W. Stose8 in which E. 0. Ulrich collaborated in the study of the Shenandoah limestone and Martinsburg shale. Further stratigraphic and paleontologic details of these rocks were given by E. 0. Ulrich in his " Revision of the Paleozoic System " in 19.11/

BIBLIOGRAPHY

1788

JEFFERSON, THOMAS. Notes on the State of Virginia. Phila., 1788. Sm. 8vo. 244 pp.

The author gives many interesting facts and speculations concerning the geology about Harper's Ferry. Fully ten editions of this book were published in different places between 1782 and 1832, each with different number of pages.

1 Amer. Jour. Sci., 3d series, vol. xliv, pp. 469-482.

2 Nat. Geog. Mag., vol. v, pp. 84-88; Sci. Am. Supp., vol. xxxvii, pp. 14753-14754.

3 Fourteenth Ann. Rep. U. S. Geol. Surv., part ii, 1894, pp. 285-395, pis. xix- xxxix.

4 Johns Hopkins University Circular No. 84, vol. x, 1890, p. 32.

5 Journal Geology, vol. viii, pp. 655-663, figs. 1-4. 8 U. S. Geol. Survey, Geol. Atlas No. 170, 1910.

1 Bull. Geol. Soc. America, vol. xxii, No. 3, pp. 281-680, 5 pis., 1911.

MARYLAND GEOLOGICAL SURVEY 35

1809

MACLURE, WM. Observations on the Geology of the United States, explanatory of a Geological Map. (Eead Jan. 20, 1809.)

Trans. Amer. Phil. Soc., o. s. vol. vi, 1809, pp. 411-428. Broad correlations and generalizations only.

1814

MITCHILL, SAML. L. A Sketch of the Scenery in the region around Harper's Ferry where the ridge of the Blue Mountains is penetrated by the joint waters of the Potomac and Shenandoah rivers. In a letter to the editor; dated Harper's Ferry, July 4, 1812. Bruee's Amer. Min. Jour., vol. i, Xew York, 1814. pp. 211-218.

The author discusses the geology and stratigraphy along the Potomac between Har- per's Ferry and Washington and regards the slates as older than the limestones.

1817

MACLURE, WM. Observations on the Geology of the United States of America, with some remarks on the effect produced on the nature and fertility of soils by the decomposition of the different classes of rocks. With 'two plates. 12mo. Phila., 1817.

(Republished in 1818, Trans. Amer. Phil. Soc., vol. i, n. s., pp. 1-91.) A classic work giving many references to the limits and character of the geologi- cal formations in Maryland. The text and map (120 m. to the inch) represent the Cretaceous extending southwest to the Susquehanna only. All land to the southeast of " Primitive " is " Alluvium " in Maryland. Pages 105-107 deal especially with Maryland.

1834

AIKIN, WILLIAM E. A. Some notices of the Geology of the Country between Baltimore and the Ohio River, with a section illustrating the superposition of the rocks.

Amer. Jour. Sci., vol. xxvi, 1834, pp. 219-232, plate.

The most complete description of the geology of central and western Maryland published up to the time of its appearance.

DUCATEL, J. T., and ALEXANDER, J. H. Report on the Projected Survey of the State of Maryland, pursuant to a resolution of the General Assembly. 8vo. 39 pp. and map. Annapolis, 1834.

Maryland House of Delegates, Dec. Sess., 1833, 8vo., 39 pp.

Another edition, Annapolis, 1834, 8vo., 58 pp.. and map.

Another edition, Annapolis, 1834, 8vo., 43 pp., and folded table.

Amer. Jour. Sci., vol. xxvii, 1835, pp. 1-38.

36 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

Results of a preliminary survey of the state. The area and formations of the state are divided into three divisions corresponding to the present Coastal Plain, Pied- mont Plateau and Appalachian areas. Many local descriptions and references are given with marked tendency towards economic point of view.

1835

TAYLOR, RICHARD C. Review of Geological Phenomena and the deduc- tions derivable therefrom in two hundred and fifty miles of sections in parts of Virginia and Maryland.

Trans. Geol. Soc. Penn., vol. i, 1835, pp. 314-325 (with colored sections).

The paper describes various sections, one of which extends from Winchester to Harper's Ferry and thence east to within 30 miles of Baltimore. This section is pi. xvii, fig. 1.

1841

DUCATEL, J. T. Annual Report of the Geologist of Maryland, 1840. 8vo. 46 pp. (Annapolis, 1840.) Map and sections.

Another edition, 8vo., 59 pp. and 3 plates, also Md. House of Delegates, Dec. Sess., 1840, n. d., 8vo., 43 pp., 3 plates.

Considers the physical geography and geology of Allegany and Washington counties, with notes on the copper mining about Frederick.

1853

MARCOU, JULES. A Geological Map of the United States and the British Provinces of North America, with an explanatory text (etc.). 8vo. Boston, 1853.

Represents no Cretaceous on Western Shore ; most of the Eastern Shore as Alluvium and the rest of the state covered successively by bands of Metamorphlc, New Red, Metamorphic, Silurian and Devonian. No Carboniferous is represented within the limits of the state (?).

1855

MARCOU, J. Resume explicatif d'un carte geologique des Etats-Unis et des provinces anglaises de 1'Amerique.

Bull. Soc. G4ol. Fr., 2 ser., tome xii, 1855, pp. 813-936; colored geological map. Explanation of map itself, so far as related to Maryland, apparently based on Maclure.

1856

HITCHCOCK, E. Outline of the Geology of the Globe and of the United States in particular, with geological maps, etc. 8vo. Boston, 1856. (3ded.)

In discussing the areal distribution of the different formations he frequently men- tions Maryland, giving reasons for location of the lines on his maps.

MARYLAND GEOLOGICAL SURVEY 37

1858

ROGERS, H. D. The Geology of Pennsylvania. 2 vols. (Vol. II in two parts) and maps. 4to. Phila., 1858.

This work containing frequent references to the Maryland extension of formations studied in Pennsylvania, besides giving the typical sections, terms, fossils, etc.

1860 . ..

TYSON, P. T. First Eeport of Philip T. Tyson, State Agricultural Chemist, to the House of Delegates of Maryland. Jan., 1860. 8vo. 145 pp. Annapolis, 1860. Maps.

Md. Sen. Doc. (E). Md. House Doc. (C).

Deals with the rocks and soils, fertilizers, etc., and explains the accompanying geological map.

1875

FONTAINE, WM. M. On some Points in the Geology of the Blue Ridge

in Virginia.

Amer. Jour. Sci., 3d ser., vol. ix, 1875, pp. 14^22, 93-101. (Abst.) Geol. Record, 1875, London, 1877, p. 119.

Includes a few notes on Catoctin Mt., and the argillites of Point of Rocks and Harper's Ferry, pp. 15-17. The first paper deals with some of the general problems involved in a study of the Blue Ridge, and the illustrations are mostly taken from that portion of the range, near the Potomac River. The second paper deals with the area about Lynchburg and southward.

— . On the Primordial Strata of Virginia.

Amer. Jour. Sci., 3d ser., vol. ix, 1875, pp. 361-369, 416-428, 3 figures.

(Abst.) Geol. Record, 1875, London, 1877, p. 119.

Refers briefly to the geology of Harper's Ferry (p. 362) and to the folds at "Cement Mill" near Hancock (p. 364). Geology of the Harper's Ferry region, pp. 422-423.

1876

HUNT, T. STERRY. Geology of Eastern Pennsylvania, Proc. Amer. Assoc. Adv. Sci., vol. xxv, 1876, pp. 208-212.

Considers the Blue Ridge in Maryland to be Montalban and Huronian with no Laurentian.

1879

FRAZER, PERSIFOR, JR. Fossil (?) Forms in the Quartzose Rocks of the Lower Susquehanna, with plate. (Read April 4, 1879.)

Proc. Amer. Phil. Soc., vol. xviii, 1880, pp. 277-279.

Deals with some curious indeterminate forms from Frazier's Point, Cecil County. Letters by Whitfleld and Hall.

38 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

1880 DANA, J. D. Manual of Geology. 3d ed.

Maryland, pp. 236, 243, 419, 455, 490, 494-5.

FRAZER, PERSIFOR, JR. The Geology of Lancaster County, Pa.

Kept. 2d Geol. Surv., Pa., ccc. Harrisburg, 1880 atlas.

Deals with the geological formations along the border of the state and their extension into Maryland.

LESLEY, J. P. On a slab of roofing slate covered with casts of Butho- trephis flexuosa from the Peach Bottom Slate Quarries. (Read Dec., 1879.)

Proc. Amer. Phil. Soc., vol. xviii, 1880, pp. 364-369.

This paper gives the history of the find, its determination by Lesquereux, analy- sis of slate and remarks by Frazer.

— . A Hudson River fossil plant in the roofing slate that is associated with the chlorite slate and metamorphic limestone in Mary- land, adjoining York and Lancaster counties, Pennsylvania.

Amer. Jour. Sci., 3d ser., vol. xix, 1880, pp. 71-72.

Buthotrephis flexuosa (determined by Lesquereux) in the Peach Bottom slates, Silurian age inferred. Extract from a letter.

1882

SCHARF, J. T. History of Western Maryland, being a history of Frederick, Montgomery, Carroll, Washington, Allegany, and Garrett counties from the earliest period to the present day. 2 vols. 4to. Phila., 1882. . Topography and Geology by P. R. Uhler. pp. 13-46.

1884

FRAZER, P., JR. The Peach Bottom Slates of Southeastern York and Southern Lancaster counties.

Trans. Amer. Inst. Min. Eng., vol. xii, 1884, pp. 355-358. Plates and section.

(Abst.) Amer. Jour. Sci., 3 ser., vol. xxix, 1884, p. 70.

Discussion of a section along the Susquehanna River northward from the Mary- land line. Also a letter from Prof. James Hall regarding the probable age of the slates, which he considers are either the Hudson River or the Quebec group from the presence of forms allied to Holymenites, Lamnantes lagranger and graptolithus.

ROGERS, WILLIAM BARTON. A reprint of Annual Reports and other papers on the Geology of the Virginias. Sm. 8vo. Appleton, 1884.

MARYLAND GEOLOGICAL SURVEY 39

WALLING, H. F. Topographical Indications of a Fault near Harper's Ferry.

(Abst.) Bull. Phil. Soc., Washington, vol. vi, 1884, pp. 30-32.

Mentions the discontinuous extension of the Blue Ridge at Harper's Ferry in sup port of increased corrugation and steepness of dip eastward with reversed folding. The downthrow to the west.

1886

FRAZER, PERSIFOR, JR. General Notes. Sketch on the Geology of York County, Pennsylvania. (Read Dec. 4, 1885.)

Proc. Amer. Phil. Soc., Phila., vol. xxiii, 1886, pp. 391-410. Discussion of the general structure equally applicable to Maryland.

1890

KEYES, CHARLES EOLLIN. Discovery of fossils in the limestone of

Frederick County, Maryland.

Johns Hopkins Univ. Cir. No. 84, vol. x, 1890, p. 32.

Gives a geological section and description of Frederick Valley and enumerates the fossils found there.

MACFARLANE, J. R. An American Geological Railway Guide. 2d ed. 8vo. 426 pp. Appleton, 1890.

Maryland notes based on data from Uhler, Williams, Fontaine and Chester.

1891

GEIGER, H. R., and KEITH, ARTHUR. The Structure of the Blue Ridge near Harper's Ferry. (Read Dec., 1890.)

Bull. Geol, Soc. Amer., vol. ii, 1891, pp. 155-164, plates iv and v.

(Abst.) Amer. Geol., vol. vii, 1891, p. 262; Amer. Nat, vol. xxv, 1891, p. 658.

The authors conclude that the sandstones are not Potsdam, as previously considered, but Upper Silurian. The paper is accompanied by geological map and sections.

KEYES, CHARLES ROLLIN. Paleozoic fossils of Maryland.

Johns Hopkins Univ. Cir. No. 94, vol. xi, 1891, pp. 28-29. Enumerates the fossils and type localities.

— . A Geologic Section across the Piedmont Plateau in Maryland. Bull. Geol. Soc. Amer., vol. ii, 1891, pp. 319-322. (Published separately, 1890.) (Abst.) Amer. Geol., vol. viii, 1891, p. 331.

Besides the general treatment of the structure from Washington to Catoctin Mt., there is a very brief discussion of structure of Sugar Loaf Mt. p. 322.

40 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

WALCOTT, C. D. Correlation Papers — Cambrian. Bull. U. S. Geol. Surv., No. 81, 1891. House Misc. Doc., 52d Cong., 1st sess., vol. xx, No! 25.

Based chiefly on Tyson's Repqrt, pp. 133, 287, 290. For problems unsolved see pp. 328-383.

1892

KEITH, ARTHUR. The Geologic Structure of the Blue Ridge in Mary- land and Virginia.

Amer. Geol., vol. x, 1892, pp. 362-368.

Broadly considered, the region is an anticline, where an arch is crumpled into several synclines and broken by faults till the resultant structure is quite complicated.

LESLEY, J. P. A Summary description of the Geology of Pennsylvania. 3 vols. Harrisburg, 1892.

Numerous references to formations passing southwards into Maryland.

WALCOTT, C. D. The Geologist at Blue Mountain, Maryland.

Nat. Geog. Mag., vol. 5, 1892, pp. 84-88.

Sci. Amer. Supp., vol. 37, 1892, pp. 14753-14754.

— . Notes on the Cambrian Rocks of Pennsylvania and Mary- land from the Susquehanna to the Potomac.

Amer. Jour. Sci., 3d ser., vol. xliv, 1892, pp. 469-482.

The portion of Maryland studied lies in the Blue Ridge and Catoctin mountains from Mechanicstown (Thurmont) to Monterey, Pa., along the W. M. R. R. and southward to Harper's Ferry, W. Va.

1893

WILLIAMS, G. H. (The Appalachian Region and the Itinerary from Washington, D. C., to Cumberland, Maryland.)

Geological Guidebook of the Rocky Mt. Excursion, Compte Rendu de la 5me Ses. Congres Geolog. Internat. Washington, 1893, pp. 268-279.

House Misc. Doc., 53d Cong., 2d sess., vol. xiii, No. 107, pp. 268-279.

Summary of the local geology along the route.

WILLIAMS, G. H., and CLARK, W. B. Geology of Maryland.

Maryland, its Resources, Industries and Institutions, Baltimore, 1893, pp. 55-89.

A general summary of the geology of Maryland with many illustrations and local references.

WILLIS, BAILEY. The Mechanics of Appalachian Structure.

13th Ann. Rept. U. S. Geol. Surv., 1891-92, pt. 2, Washington, 1893, pp. 211-281, plates and maps.

The discussion includes illustrations from Maryland, and its conclusions are appli- cable to the western portion of the state.

MARYLAND GEOLOGICAL SURVEY 41

1894

KEITH, ARTHUR. Geology of the Catoctin Belt.

14th Ann. Kept. U. S. Geol. Surv., 1892-93, Washington, 1894, pt. ii, pp. 285-395, maps and plates.

House Exec. Doc., 53d Cong., 2d sess., vol. xvii, p. 285. (Rev.) Sciences, n. s., vol. ii, 1895, p. 97. A full discussion of the area studied.

— . Harper's Ferry Folio, Explanatory Sheets.

U. S. Geol. Surv. Geol. Atlas, folio No. 10, Washington, 1894. Brief epitomized discussion of the local geology, structure and geological history of the area included.

1896

DORSEY, CLARENCE W. The Soils of the Hagerstown Valley.

Md. Agr. Exp. Sta. Bull. No. 44, College Park, 1896.

A study of the soils resulting from the disintegration of the Cambrian sandstone, Hudson River shales and Trenton limestones. Distinguished five types.

WALCOTT, C. D. The Cambrian Rocks of Pennsylvania.

Bull. U. S. Geol. Surv. No. 134, 1896. House Misc. Doc., 54th Cong., 2d sess., No. 24.

Contains incidental reference to his work with Keith in Frederick County and also to the southern continuation of Pennsylvania formations.

WILLIS, BAILEY. The Northern Appalachians.

The Physiography of the United States.

Geographic Monographs I, American Book Company, 169 pp., 1896.

A study of the present topography and its origin.

1897

CLARK, WILLIAM BULLOCK. Historical sketch embracing an account of the progress of investigation concerning the physical features and natural resources of Maryland.

Md. Geol. Surv., vol. i, pp. 43-138, pis. ii-v, 1897.

— . Outline of present knowledge of the physical features of Maryland, embracing an account of the physiography, geology, and mineral resources.

Md. Geol. Surv., vol. i, pp. 141-228, pis. vi-xiii, 1897.

Description of the physiographic features of the state, the character and distribution of the igneous and sedimentary rocks, and the mineral resources.

42 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND

1899

ABBE, CLEVELAND, JR. A general report on the physiography of Mary- land.

Md. Weather Service, vol. i, pp. 41-216, pis. iii-xix, figs. 1-20, 1899. Discusses the physiographic features of the Piedmont Plateau and Appalachian provinces in Maryland.

CLARK, WILLIAM BULLOCK. The relations of Maryland topography, climate, and geology to highway construction.

Md. Geol. Surv., vol. iii, pp. 47-106, pis. iii-xi, figs. 1-3, 1899.

1900

PROSSER, CHARLES S. The Shenandoah limestone and Martinsburg shale.

Jour. Geol., vol. viii, pp. 655-663, figs. 1-4, 1900.

Describes the lithologic and faunal characters of the formations In adjacent portions of Maryland and West Virginia.

ULRICH, E. 0., and SCHUCHERT, CHARLES. Paleozoic Sjas and barriers in eastern North America.

N. Y. State Mus., Bull. No. 52, pp. 633-663, 1 pi.

1906

CLARK, WILLIAM BULLOCK. Report on the physical features of Mary- land, together with an account of the exhibits of Maryland mineral resources made by the Maryland Geological Survey.

Maryland Geol. Survey (Special Publications, vol. vi, pts. 1 and 2), 284 pp., 30 pis., 19 figs., geol. map. (in pocket), 1906.

A general account of the physiography, geology and mineral resources of the state.

1907

MARYLAND GEOLOGICAL SURVEY.

(Geological) map of Maryland, prepared by Maryland Geological Survey, Wm. Bullock Clark, State Geologist, 1907, Scale 1 : 187, 500.

BASSLER, BAY S. Cement and cement materials (of Virginia). In Watson, T. L., Mineral Resources of Virginia, pp. 86-167, 10 pis., 14 figs., 1907.

MARYLAND GEOLOGICAL SURVEY 43

1908

STOSE, GEORGE W. The Cambro-Ordovician limestones of the Appa- lachian Valley in southern Pennsylvania. Jour. Geology, vol. xvi, No. 8, pp. 698-914, 1908.

BASSLER, KAY S. Cement materials of Western Virginia. Econ. Geology, vol. iii, No. 6, pp. 503-524, 4 figs., 1908.

PEABODY, CHARLES. The exploration of Bushey cavern, near Cave- town, Maryland.

Phillips Academy, Andover, Massachusetts, Dept. of Archaeology, Bull, iv, pt. 1, pp. 3-25, 8 pis., 1908.

1909

MATHEWS, EDWARD BENNETT, and GRASTY, JOHN SHARSHALL. Ee- port on the limestones of Maryland, with special reference to their use in the manufacture of lime and cement.

Maryland Geol. Survey, vol. viii, pp. 225-477, 14 pis., 12 figs., 1909.

BASSLER, KAY S. The Cement Resources of Virginia west of the Blue Kidge.

Virginia Geol. Surv., Bull No. 2A, 309 pp., 30 pis., 30 figs., 1909.

1910

SCHUCHERT, CHARLES. Paleogeography of North America. Geol. Soc. America Bull., vol. xx, pp. 427-606, 56 pis.

STOSE, GEORGE W. Description of the Mercersburg-Chambersburg dis- trict, Pennsylvania.

U. S. Geological Survey, Geol. Atlas U. S., Mercersburg-Chambersburg folio (No. 170), library edition, 19 pp., 8 pis. (maps, sections, and illustrations sheets), 5 figs., 1909; field edition, 144 pp., 6 folded maps, 10 pis., 4 figs., 1910.

Describes the topographic features, the general geology, the occurrence, character, and relations of pre-Cambrian volcanic rocks, and of Cambrian, Ordovician, Silurian and Devonian formations, and geologic structure, the geologic history, and the economic resources.

1911

ULRICH, EDWARD 0. Revision of the Paleozoic Systems. Geol. Soc. America, Bull. vol. xxii, No. 3, pp. 281-680, 5 pis.

44 THE CAMBRIAX AND ORDOVICIAN DEPOSITS OF MARYLAND

EATON, H. N. The geology of South Mountain at the junction of Berks, Lebanon, and Lancaster counties, Pennsylvania.

Jour. Geology, vol. xx, No. 4, pp. 331-343, 2 figs., May-June, 1912. Describes the occurrence, character and relation of pre-Cambrian, Cambrian, Ordo- vician and Triassic strata and the structural conditions.

JANDORF, MORTON LEHMAYER. Preliminary report on the York Valley limestone belt in York County.

Pennsylvania Topog. and Geol. Survey, Kept. 1910-1912, pp. 50-129, 14 pis. (incl. maps), 1912.

MOORE, ELWOOD S. Siliceous oolites and other concretionary structures in the vicinity of State College, Pennsylvania.

Jour. Geology, vol. xx, No. 3, pp. 259-269, 7 figs., April-May, 1912: Abstract, British Assoc. Adv. Sci., Kept. 81st Meeting, p. 390, 1912.

Describes the occurrence and geologic relations and discusses the origin of siliceous oolites.

STOSE, GEORGE W., and SWARTZ, CHARLES K. Description of the Pawpaw and Hancock quadrangles (Maryland-West Virginia-Pennsyl- vania).

U. S. Geol. Survey, Geol. Atlas U. S. Pawpaw-Hancock folio (No. 179), 24 pp., 11 figs., 9 pis. (maps, sections, and illustrations), 1912; field edition, 176 pp., 11 figs., 20 pis., 6 folded maps (in pocket), 1912.

Abstract, Washington Acad. Sci. Jour., vol. ii, No. 16, p. 410, October 4, 1912.

Describes the topography, the character, occurrence, and relations of Cambrian, Ordovician, Silurian, Devonian, and Carboniferous formations, and of Tertiary, and Quaternary deposits, the geologic structure, the geologic history, and the mineral resources.

WILLIS, BAILEY. Index to the stratigraphy of Xorth America.

U. S. Geological Survey, Prof. Paper, 71, 894 pp., 1 pi. (geological map in 4 sheets in separate case).

Brief notes on Maryland stratigraphy are given in the compilation of data used in the preparation of the geologic map of North America.

1913

BROWN, THOMAS C. Notes on the origin of certain Paleozoic sedi- ments, illustrated by the Cambrian and Ordovician rocks of Center County, Pennsylvania.

Jour. Geology, vol. xxi, No. 3, pp. 232-250, 7 figs., 1913; (Abst.), Geol. Soc. America, Bull. vol. xxiv, No. 1, p. 112, March 24, 1913.

Discusses the origin of conglomerates, oolites, and sandstones of Ordovician and Cambrian age.

MARYLAND GEOLOGICAL SURVEY 45

The subject of ancient or geologic geography for which the term " paleogeography " was proposed in 1872 by T. Sterry Hunt and was prominently employed by Robert Etheridge, the English paleontologist, in 1881, has become such an important branch of stratigraphic geology that to-day no general stratigraphic discussion is complete without an attempt to indicate the distribution of the land and water of the time. Since 1896 when Canu published his " Essai de paleogeographie " the term has been frequently employed.

Paleogeographie maps have been prepared in America since 1863 when James D. Dana published several generalized sketches of the Azoic, Cretaceous, and early Tertiary periods, in the first edition of his Manual of Geology. Since then over 500 paleogeographie maps have appeared, about one-half of which refer to North America. Until recent years most of these maps were subject to the criticism that they covered too much time and therefore were too generalized.

Schuchert, in 1908, in his " Paleogeography of North America," pub- lished a series of maps based upon the most precise correlations and the narrowest time limits that had hitherto been attempted. This work, which was prepared in collaboration Avith all the leading American stratigraphers and paleontologists, brought out with excellent clearness many new features, especially the oscillatory nature of the continental seas. This publication marks a great 'advance in the science of paleo- geography. In spite of efforts to the contrary, some of these maps, as was recognized by their author, covered too long a time period, and are subject to the criticism just mentioned.

Since 1908 a great amount of new data on the stratigraphy and paleontology of American early Paleozoic formations has been accu- mulated and to-day maps covering the geography of a single formation are possible. Maps illustrating the early Paleozoic divisions of the geological column were prepared by E. 0. Ulrich and revised at frequent intervals as new facts were obtained. But few of these have hitherto been pub- lished, but the writer has obtained permission to reproduce in this volume

46 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

all of the maps covering the formations here under discussion. These are inserted in their appropriate place in the text.

It must be remembered that in these maps the shore lines are more or less hypothetical and do not show the bays and other features of present- day strands. It must also be remembered that the present-day base maps do not accurately represent the continents of past times, because the latter, especially in the mountainous areas, have suffered great compression.

Although it is evident that the portion of Maryland covered by the Cambro-Ordovician rocks is too small a part of the North American continent to reveal much of the paleogeography, still it may be noted from the accompanying maps that western Maryland has been much concerned in the continental oscillation and other earth movements which occasioned the repeated invasions and withdrawals of the sea. In order to plot these sea invasions not only must the distribution of the marine sediments of the time be determined and the ancient shore lines thus approximated, but also the particular oceanic basins from which the several fossil faunas have migrated must be ascertained. The waters which have repeatedly flooded the continent have come from the Arctic, Atlantic and Pacific oceans and the Gulf of Mexico, and each brought with it such samples of its own particular life as were available and suited to existence in shallow epicontinental seas.

Comparative studies of the fossil faunas have shown them to have had a considerable sameness in composition when derived from the same oceanic source, and to have had great unlikeness to contemporaneous faunas that originated in other oceanic basins. This appears to indicate not only that the life in the several oceanic basins evolved more or less independently, but also that each maintained in recognizable measure its individual characteristics. These distinctive facies were perhaps never less and may often have been greater than now. At any rate Ordovician faunas of Arctic origin are at least as distinct from approximately con- temporaneous ones of Gulf origin as the life of the Arctic Ocean to-day is different from that of the Gulf of Mexico. Appreciating these distinc- tions paleontologists are succeeding very well in discriminating the faunas

MARYLAND GEOLOGICAL SURVEY 47

that came in from the east or south from those that invaded the continent from the north or west.

The underlying principles of the science of paleogeography and the methods employed in the preparation of paleogeographic maps have been discussed in detail by Ulrich.1 In brief the study of first, fossil faunas and floras, and second, of the phenomena expressed under the general name of diastrophism, afford the data for such maps. In the study of the ancient life forms, conclusions of value are reached first, by determining the areal distribution of certain associations of species of land and water organisms, and second, by the discovery of their place of origin.

The second method of study, based on diastrophism depends upon the idea of essentially permanent depressions and elevations of the earth's surface. According to this view the surface of the continent can be divided into (1) positive areas that have been rarely if ever submerged, this being shown by the distribution of the sedimentary rocks around them ; and (2) negative areas which often received deposits from waters of one or another of the oceanic basins whenever by subsidence they were brought below sea level. A paleogeographic map therefore is produced by plotting the isolated occurrences of a definitely identified fossil fauna and connect- ing them with the ocean of their origin by sea ways within the negative areas.

From the study of the criteria of paleogeography it becomes apparent that the Paleozoic epicontinental seas occupied mostly small, shallow, often disconnected, basins, communicating with the nearest oceanic basin. In general they must have been much like Hudson Bay, which may be regarded as a modern representative of an American interior continental sea. Many of these land basins were filled and emptied many times, occasionally receiving their water from the Atlantic and at other times from the Arctic, and ofttimes from the Gulf of Mexico. Naturally, with each change in the source of the waters, the geographic pattern differs considerably, and at times fundamentally, from the next preceding. In

i Bull. Geol. Soc. Amer., vol. xxii, 1911, No. 3, pp. 281-680, 5 pis. and Compte Rendu, XII session du Congres geologique international, pp. 593-667.

48 THE CAMBRIAN AND OKDOVICIAX DEPOSITS OF MARYLAND

Ordovician.	Canadian.		r»5#&[S^]S^T5^^,	Finely laminated pure magnesian limestone with cauliflower and other cherts at top. 440 feet.
	1 1 1
_ , 1 . 1 1 1
1 1	Massive pure dove, gray, and magnesian limestone containing the Turritoma fauna in its upper part. 575 feet.
1 1 1
3eekmantown limestone.	1 1 ' 1 ' 1 '
1 sE ,'o 3
	Blue and dove limestone, cherty in upper part and containing the horn-like fossil Ceratopea. 250 feet.
I I /
/ 1
1 ' °! ' ?' i r I	Cherty oolitic limestone, dove-colored, pure lime- stone and dense textured pink marbles. Basal 60 feet contains Cryptozoon steeli and weathers into yellow platy chert. 600 feet.
	1 ' / / 1
II 1 1
is & » e ti) ! f> 6' » <3
	" '.~|~ '„ | o e | . V
^^^^^
Stonehenge member. The upper half of massive blue to gray, limestone with contorted siliceous laminations interbedded with edgewise conglom- erates and oolite. The lower half gray, pure limestone, weathering white. 500 feet.
-^^i^^^iJ-f<yJi^-fJ!rJ/
1 1
1 1
1 1
C .n	Middle Cambrian (Acadian). Ozarkian.	Conococheague limestone.	3°*t~iri^ir~	M ' d k bl 1' t 1 ' 1 h d d h • th'
^^^^c^S	siliceous contorted laminae, weathering into sandy shale fragments. Edgewise conglomerate, oolite and chert abundant at the base. 1600 feet.
i-i t i- tr^f-L
S25E5HxH
r* r11" ~T r1 h1
Elbrook formation.		Light-blue and gray shaly limestone, weathering into shale fragments. Massive dolomitic and siliceous limestone developed in the middle part
	and dark-blue massive limestone at the base. 3000 feet.
.'I.-. .-I.-.: : / •-•.-. /.-.
'•••!•• ' • ' ' -I
^^^-=^=^i— ^
i 1
Waynesboro		Siliceous gray limestone and calcareous sandstone at base, massive limestone and marble in middle
1 i' i '
formation.	1 1 1	portion and red to purple siliceous shale at top. Forms low ridges suitable for fruit culture. 1000 feet.
£^-^2^=^!^-
Lower Cambrian (Waucoban).	Tomstown limestone.	i i i i i	White to pink shaly marble weathering to vellow- ish shale fragments, with also massive dark-blue magnesian limestone. Upper beds weather into blocky, black-banded chalcedonic chert. 1000 feet +.
i i
i i i
Antietam sandstone.	SSSSSs1	Coarse-grained white to bluish-gray sandstone and quartzite, weathering readily to sand. Contain numerous Scolithus. 800 feet.
Harpers shale.	5^—gssr	Bluish-gray sandy shales, slate, schist, and thin flaggy sandstones. 1200 feet.
^c^ ^r"~ —
l^^S-^-SE^S^^E:.
^==^^~^^
Weverton sandstone.	i.* ;.;:.'..' «"i :.'.'.'; :.•»•.•;:	Massive, white and purple, coarse, feldspathic sand- stone and quartzite, forming mountain ridges. 800 feet.
Loudon formation.	=~ — — —	Dark slates, shales, sandstones, and marbles. 500 feet.
Pre- cam- brian.		y^^fe^g^Tr^ f^lS^Tsktt ^j^F^Ww^f	Altered rhyolitic lava and basalt flows.

FlG. 1. — COLUMNAR SECTION OF THE CAMBRIAN, OZARKIAN AND CANADIAN STRATA OF MARYLAND AND NEIGHBORING STATES.

MARYLAND GEOLOGICAL SURVEY

40

Silu- rian.	Tuscarora sandstone.	.•••/.	Massive white quartz sandstone and conglomerate.
Ordovician.	Cincinnatian.	Juniata formation.	m .., ,.	Unfossiliferous, soft, red sandstone and inter- bedded red shale. 400 feet.
;: .'.'.'.'.;' .'.''.'. •; '. '. v.v
	'- '— :_L .'^-^fJ— ; — '^^*^=f=:	Unfossiliferous gray sandstone, probably of Upper Maysville age. (Oswego sandstone.) 150 feet.
	— .-, v.^vt^T-:: ~."-:~-^rr^-	Unfossiliferous gray sandstone with Orthorhyn- chula linneyi zone at top. Lower Maysville in age. 300 feet.
Martinsburg shale.	''.'.''.'.'.."^''.'Tr.' ••- ••j77^i4_	Yellow shale and calcareous sandstone in upper half and soft greenish to yellow shaly sandstone and shale in lower part. Fossils of Eden age at several horizons. 1000 feet +.
	g-^gS^sis	Dark gray Unfossiliferous shale in upper half and
Mohawkian.			black carbonaceous fissile shale in lower half. Probably of Trenton and Utica age. 1100 feet -K
	T	Calcareous dark shale with Corynoides fauna. Thin-bedded, limestone with Sinuites fauna. TJreencastle bed. Heavy bedded impure limestone. (Not developed in Maryland.) 0-200 feet.
^3 — ^ — r — "— r- —
	i	Christiania bed. Thin-bedded calcareous shales and shaly limestone. 0-270 feet.
	I i
Chambersburg limestone.		Nidulites bed. Compact dark gray, thick and thin- bedded limestone. 200-300 feet.
I
_tl_^r_
j^E^^-T ,!„-- ^rW-T-^f-^-r- ^r	Echinospherites bed. Dark blue, argillaceous, cobbly limestone. 40-50 feet.
	i 1	Tetradium cellulosum bed. Fine-grained dove and subgranular limestone. 0-200 feet.
	1-
Caryocystites bed. Coarsely crystalline to sub- crystalline limestone. 0-175 feet.
	; i / ,'
	r •
Chazyan.		-s^^v	Massive fine-grained dove-colored limestone. 300 feet +.
	1
	1 1 1
	1
	i i [
	0 |o cu c^> c=> | a <=,	Blue to gray compact granular to oolitic limestone with Maclurites magnus fauna. Weathers into black, blocky chert. 200 feet.
Stones River	=7|<=, ^ 0 | = V 0
	^ , i „ — i j-T^ i '-^ —
	i i	Massive dove limestone interbedded with magnesian layers. Cauliflower chert or silicified edgewise conglomerates present at base. 600 feet -<-.
	i
		Cherty top of Beekmantown limestone.
	1
	^S__O) &£^2—f^5^£3 ^oj^oj C3,

PlG. 2. — COLUMNAR SECTION OF THE ORDOVICIAN ROCKS OF MARYLAND AND NEIGH- BORING STATES.

50 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

the Appalachian region the seas were often contained in narrow troughs which connected at some point with the Atlantic, although occasionally these troughs communicated at both ends with the ocean.

The complete changes in the source and direction of the faunal in- vasions are well shown in some of the maps of North America in Early Paleozoic time. For example the Gulf invasion of Lower Black Eiver (Lowville) time is superseded by an incursion from the Arctic in the Middle Black Eiver (Decorah) and this is followed by one which seems to have come in from the west.

STEATIGEAPHIC AND PALEONTOLOGIC CHAEACTEEISTICS

Throughout the Appalachian provinces the Early Paleozoic strata com- prised in the Cambrian and Ordovician systems may be conveniently arranged into three great phases of sedimentation — the lowest of sand- stone, quartzite, and sandy shales of Lower Cambrian age, next limestone deposits extending from uppermost Lower Cambrian to the lower part of Middle Ordovician times, and last a shale phase covering the remaining Middle and Upper Ordovician. In Appalachian Maryland each of these three phases is well developed, their combined thickness reaching 16,000 feet. Of this total, the lower division comprises over 3300 feet, the middle limestones over 10,000 feet, and the upper shales 2400 feet. These thick- nesses vary in different parts of the Appalachians. As a rule they arc greatly diminished to the north of Maryland and much increased in the states to the south. Columnar sections of the Cambrian and Ordovician rocks of Maryland and neighboring states are presented on pages 48 and 49. while a correlation table of these strata is given on page 51.

These three quite different lithologic divisions outcrop in equally dis- tinct geographic areas. The siliceous rocks are confined to the Blue Eidge province, the limestones form the floor of the Appalachian Valley, and the shales, although sometimes occurring as a great infold or syncline in the limestone in the middle of the Valley, are best developed in the eastern ranges of the Allegheny ridges.

52 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

East of the Blue Eidge province, sandstone metamorphosed into quartz- ites, limestone changed into marbles, and shales into slates or schists, outcrop in small patches at numerous points on the Piedmont Plateau. Although fossil evidence regarding the age of these latter strata is in most cases wanting, it is believed that they represent at least portions of the three phases of deposition farther west. Their correlation, however, cannot be confirmed until the geologic history of the Piedmont province has been studied in detail. The present volume is therefore devoted more to the discussion of the stratigraphy and paleontology of the Cambrian and Ordovician rocks of the Blue Ridge and more western provinces, although for the sake of completeness, brief notes on the Piedmont strata of apparently the same age are introduced in their appropriate places.

CAMBRIAN SILICEOUS FORMATIONS

Although the siliceous Lower Cambrian rocks outcrop in long but interrupted stretches from Vermont to Alabama, they differ so greatly in character and sequence from place to place that none of the formations, if any were ever so extended, are unquestionably recognizable throughout the whole Appalachian province. A few widely separated areas have been studied in detail, but, on account of difficulties in correlation, differing sets of local names had to be applied to the formations distinguished in each. The excellent exposure in the gorge of the Potomac Eiver where it breaks through the Blue Ridge early attracted the attention of geologists to the Maryland-Virginia section. The sequence of formations here determined and named has been traced to the north across the state into Pennsylvania and proved satisfactory, and is generally accepted as the standard for the Lower Cambrian in the north middle Appalachian region. These formations and their thicknesses arranged in geologic order, are as follows :

Table of Maryland Lower Cambrian Siliceous Formations

Feet

Antietam sandstone. Coarse grained white to bluish sandstone 800

Harpers shale. Bluish gray sandy slates and schist 1200

Weverton sandstone. Massive white and purple sandstone and quartzite. . 800 Loudon formation. Dark slates, sandstone, shales and marbles 500

MARYLAND GEOLOGICAL SURVEY 53

THE LOUDON FORMATION

The oldest sedimentary Paleozoic rocks in Maryland are argillaceous dark slates, sandy shales, blue limestones, white marble, gray sandstone, and quartz conglomerate, immediately overlying the crystalline rocks and known collectively as the Loudon formation, named from Loudon County, Virginia, where all the members are well displayed. Weathering of the unconformably underlying Catoctin schist gave rise to a great variety of sediments, Avhich accounts for the diverse strata composing the succeeding formation. A fine grained, dark slate usually makes up the greater part of the Loudon formation, but almost all of the other varieties of sedimentary rocks, especially coarse and fine conglomerate, shale, and pure limestone are locally developed.

The formation outcrops in Maryland in depressions and valleys with lines of small hills and ridges. It gives rise to a thin, micaceous, sandy soil of little importance agriculturally. The rocks are exposed in long narrow belts along several lines of outcrop, namely, the east side of Elk Ridge, both sides of South Mountain and both sides of Catoctin Mountain. In the granite and schist area between Catoctin Mountain and South Mountain a few narrow synclines made up of the coarser deposits of the formation are also found. The finer and thinner strata of the formation occur only in the mountain areas mentioned above where the Weverton quartzite overlies the Loudon formation. The limestone occurs as lenses in the slate, and in Maryland has been found only along a line just west of Catoctin Mountain for a distance of a mile or two north of the Potomac River. This limestone is usually metamorphosed into marble, but the marbles are interbedded with slate and schist and are almost always too poorly developed to be worked for commercial purposes. However, almost every outcrop of this limestone has in the past afforded rock for lime.

The black slate makes up a large part of the Loudon formation in Maryland, especially along the Catoctin Mountain line of outcrop. Here the thickness is not over 200 feet, but along the Blue Ridge at Turner's Gap, 10 miles north of the Potomac River, a thickness of 500 feet has been measured. All trace of the original bedding in these slates has been

54 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

lost by metamorphism during the folding of the rocks. The Loudon slate can be f ouncl at localities one mile east of Harper's Ferry and half a mile south of Rohrersville, Maryland, with coarse fragments of the Catoctin schist such as epidote and jasper imbedded in it.

The conglomerates of the Loudon formation, with few exceptions, are confined to the synclinal areas where the Weverton sandstone is not present. These conglomerates are limited in extent and are composed of quartz, granite, jasper, and epidote boulders imbedded in the usual black slate. Grains of magnetite and ilmenite washed from the Catoctin schist are present in many of the beds. Sandstones likewise occur, but these are thin and unimportant in Maryland, their greatest development being south of the Potomac River.

The Loudon formation as a whole has been subjected to much meta- morphism and its various members exhibit the usual metamorphic prod- ucts, namely, quartzite, slate, schist, and marble. The alteration is most marked in the argillaceous beds where all trace of their original stratifica- tion has been lost in the change to slate and schist. This slate and the few marble areas weather readily, forming low ground. The more siliceous rocks, metamorphosed into quartzite, resist weathering and as a result form the low hills or ridges of the Loudon areas.

No fossils have been discovered in the Loudon formation, the conditions of sedimentation being unfavorable for the preservation of organic re- mains. These rocks, however, apparently mark the beginning of the siliceous Lower Cambrian deposits, the age of which is determined by paleontological evidence in the overlying Harpers shale and Antietam sandstone.

THE WEVERTON SANDSTONE

The prominent outcrops in the gorge of the Potomac River at the south end of South Mountain near Weverton, Maryland, consist of massive beds of fine, pure, white and purple sandstone, quartzite, and conglomerate, overlying the basal Cambrian Loudon formation. These strata, termed the Weverton sandstone, are the most resistant of all the Cambrian and Ordovician deposits, and for that reason they are the main mountain-

56 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

making formation of the Blue Eidge province. Elk Eidge, South Moun- tain, and Catoctin Mountain are the principal elevations in Maryland due to the resistant Weverton sandstone and it is along their crests that the formation is exposed. Sugar Loaf Mountain is the easternmost eleva- tion due to this formation.

This sandstone is composed almost entirely of siliceous fragments, mainly quartz and feldspar, firmly cemented together and often changed into quartzite. The color of the finer sandstone is white, and the coarser gray to purple. Streaks of bluish black and black sometimes occur in the white sandstone on South Mountain. Feldspathic material is present in greatest abundance at the northern end of Catoctin Mountain, but its occurrence does not change the general aspect of the formation. As a rule, however, the Weverton is usually composed of well-worn quartz grains washed clear of argillaceous material. Cross bedding is not an uncommon occurrence.

As the quartz particles forming the main mass of the Weverton sand- stones do not admit of much alteration, this formation has been subjected to comparatively little metamorphism, even when it has been greatly folded. Slight schistosity has been noted in the southern part of Catoctin Mountain, but the development of quartzite is the usual occurrence.

The Weverton sandstone varies little in composition from place to place, but the thickness is subject to much variation. Along Elk Ridge its thick- ness is about 500 feet. At the type locality near Weverton, the thickness is also about 500 feet, but northward along South Mountain this increases to 800 feet. A similar increase in thickness is seen in the Catoctin Mountain area.

This formation is not only of no value agriculturally, but the debris from it lessens the value of neighboring areas. It decays very slowly into quartz sand and its heavy blocks cover the mountain sides and the con- tiguous lowlands. The mountain streams carry great quantities of boulders of Weverton sandstone out on the surrounding areas where they are deposited as a drift formation not unlike glacial deposits. South Mountain has furnished boulders of white quartzite and sandstone, which

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE III

FlG. I. — VIEW OF THJE GREAT VALLEY FROM SOUTH MOUNTAIN AT BLUE MOUNTAIN STATION.

FlG. 2. — VIEW ALONG ROAD BETWEEN PEN MAR AND HIGH ROCK, MARYLAND, SHOWING MOUNTAIN SIDE COVERED WITH BLOCKS OF WEVERTON QUARTZITE.

57

are now spread out in all the lowland areas of the Hagerstown Valley in a strip one to two miles wide paralleling the mountain.

Fossils have not been found in this sandstone, but as it is a part of the siliceous series terminated by the Antietam sandstone, which contains a Lower Cambrian fauna, the age of the Weverton sandstone also is very probably Lower Cambrian.

THE HARPEKS SHALE

The bluish gray slate or schist exposed so prominently in the vicinity of Harper's Ferry, West Virginia, in the gorges of the Potomac and Shenandoah rivers and known as the Harpers shale, follows the Weverton sandstone in the geological column, although its outcrops are almost everywhere included between faults. In southern Maryland the Harpers shale is composed almost entirely of sandy slates with a few sandstone layers developed in its upper portion. These shales are of a dull bluish- gray color when freshly exposed, but they weather to a light greenish- gray. Northward in Maryland the sandstone layers increase in thickness until, in the region of Pen Mar, and especially at Montalto Mountain in southern Pennsylvania, a massive quartzite 750 feet in thickness is developed in the middle portion of the schist. This is the Montalto quartzite member mapped by Stose in the Chambersburg (Pennsylvania) quadrangle, but it is hardly of sufficient importance in Maryland to be distinguished as a separate unit. This Montalto member is only 20 feet thick just north of the Maryland line, but it thickens to 850 feet going northward a distance of 20 miles in Pennsylvania.

As no complete section of the Harpers shale is exposed in Maryland or even in its other areas of outcrop, its thickness is difficult to determine. Moreover one or often both sides of its areas of outcrop are cut off from adjoining formations by faults. At Harper's Ferry, the type area of outcrop, the thickness has been estimated by Keith as 1200 feet. . In southern Pennsylvania northeast of Waynesboro the thickness is increased to 2750 feet, due in part to the development of the Montalto quartzite member.

58 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

The typical outcrop of the . Harpers shale extends northward from Harper's Ferry into Maryland for several miles in a belt a mile or less in width, following the western slope of Elk Ridge until it is terminated by a fault against the Tomstown limestone, a mile south of Keedysville. A second belt of outcrop is one-half mile wide and follows the western slope of South Mountain across the state. The last and easternmost belt occurs on the eastern side of Catoctin Mountain.

The decay of the Harpers shale gives rise to soils of moderate value when its areas of outcrop are not too deeply covered with sandstone debris from the adjacent mountain sandstone ridges. As an example of the latter feature, the entire area of outcrop of this shale west of South Mountain in Maryland is covered with a thick deposit of such sandstone boulders. So far as known the only clean exposures of the shale itself are in cuts of the Western Maryland Railway in its ascent of South Mountain to Pen Mar, and in certain road and stream cuttings.

With the exception of casts of the worm burrow Scolithus lineans no fossils have been found in the Harpers shale. Its age, however, is un- doubtedly Lower Cambrian because it forms a part of the same series of siliceous sediments as the overlying Antietam sandstone which contains typical Lower Cambrian fossils.

THE ANTIETAM SANDSTONE

The Harpers shale forming the western slope and foot hills of South Mountain is found to contain an infolded sandstone formation wherever a conspicuous elevation is developed in front of the main ridge. Such front ridges of South Mountain owe their origin to coarse grained white to bluish-gray quartzite and sandstone about 500 feet in thickness, which weathers readily to a white sand. This is the Antietam sandstone, so named from the good exposures on the tributaries of Antietam Creek east of Sharpsburg, Maryland. This sandstone is .the uppermost of the mountain-making formations of the Blue Ridge province and is the last of the siliceous deposits of Lower Cambrian age. It is composed of small grains of white quartz, «vorn and assorted, cemented together by a small

MARYLAND GEOLOGICAL SURVEY f>9

percentage of carbonate of lime. Its color is usually white, but some of the upper layers change to a dull brown. Actual outcrops of the rock are very rare, but its presence can be determined readily by the numerous lumps of white sandstone strewing the surface and by its topographic form. On account of their location and the abundance of rock fragments in the soil, its areas of outcrop are unsuitable for agriculture other than the growth of fruit trees.

The Antietam sandstone does not outcrop in a continuous belt like the associated formations, but is displayed in a number of small areas just west of the main elevation of South Mountain. Its occurrence coincides with that of the Harpers shale, and indeed Keith's detailed mapping has shown that this sandstone is found only as synclinal remnants lying upon the shale. The largest of these areas in Maryland are the ridge about four miles long just east of Ponds ville and the V-shaped ridge east of Mapleville. The elevation just east of Boonsboro likewise is composed of Antietam sandstone, while a few small areas are infolded in the Harpers shale belt just north of Eohrersville. The western foot hills of Elk Ridge likewise contain a few small, scattered areas, while the larger elevation two miles east of Sharpsburg is composed almost entirely of this formation. The Harpers shale belt on the east side of Catoctin Mountain contains small, schistose, sandy beds lying above the Harpers shale which may be the metamorphosed equivalent of the Antietam sand- stone.

Except a few worm burrows in the sandstone member of the Harpers shale, the Lower Cambrian deposits in Maryland are practically un- fossiliferous beneath the upper part of the Antietam sandstone. Even here fossils are by no means common at any place. In Maryland the best locality for fossils is in the sandstones along the mountain front near Eakles Mills where fragments of Olenellus thompsoni Hall, Hyolithes communis Billings, and Obolella minor Walcott have been found by Wal- cott. These fossils are associated with the Scolithus tubes which are abundant in the upper part of the formation at practically all of its out- crops. This fauna, although small, is sufficient to determine the age of

60 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

the Antietam sandstone as Lower Cambrian. The same association of species has been found on Observatory Hill, two miles south of Keedys- ville and at a locality about one mile southeast of Smithsburg.

CAMBRIAN-ORDOVICIAN LIMESTONES

The second great phase of deposition in the Appalachian region com- prises a group of limestones which, from the fact that these strata form the floor of the great Valley, were first named the Valley limestone. In Virginia, the geographical term Shenandoah limestone was subsequently substituted for Valley limestone of the older geologists. In all the earlier maps of the central Appalachian Valley this limestone was regarded as a single formation and its thickness was supposed to approximate 5000 feet. This calcareous phase of deposition between the Cambrian siliceous rocks and the Ordovician shales is such a conspicuous feature throughout the Appalachian Valley that various local names have been applied to it. In Maryland the name Shenandoah formation was used for this limestone until comparatively recent years when geologic work in adjacent areas of Pennsylvania showed that these strata can be subdivided into seven distinct formations with an aggregate thickness of over 10,000 feet. The names, age, and thickness of these seven formations are as follows :

Table of Cambrian-Ordovician Limestones in Maryland

Feet

Middle Ordovician, Chambersburg limestone 300

Lower Ordovician, Stones River limestone 1000

Lower Ordovician ( Canadian )-Beekmantown limestone (Stonehenge mem- ber at base) 2500

Upper Cambrian (Ozarkian)-Conococheague limestone 1600

Middle Cambrian. . fElbrook formation 3000

\ Waynesboro formation 1000

Lower Cambrian-Tomstown limestone 1000

All of the above formations may be more or less readily recognized by lithologic peculiarities, by the contained fossils, by the topographic forms and residual debris which their weathering produces and by their known position in the stratigraphic sequence. Limestones of similar aspect may be found common to all the formations, but fortunately the boundary

MARYLAND GEOLOGICAL SURVEY 61

between adjoining divisions commonly is marked by one or more dis- tinctive lithologic features which aid considerably in the delimitation of the formations.

THE TOMSTOWN LIMESTONE

The lowest division of the " Shenandoah " is a thick limestone forma- tion which outcrops along the eastern edge of the Appalachian Valley just west of the Blue Ridge or the equivalent mountain range in a narrow strip often largely covered by sandstone debris from the adjacent mountain. These rocks are usually highly tilted and as a result the band of outcrop is often quite narrow. In Virginia this limestone received the designation, Sherwood limestone, and more recently the corresponding beds in southern Pennsylvania were termed the Toms- town limestone on account of their outcrop at Tomstown, Franklin County. In Maryland the area of outcrop of the Tomstown limestone is broader than usual because these strata are here not so sharply folded.

TOPOGRAPHY. — The Tomstown limestone is the most soluble of all the formations outcropping in the eastern part of the Appalachian Valley. Its outcrops therefore occur only in lowland areas. As the overlying formation, the Waynesboro, is composed in large part of sandstone and shale, it resists weathering and solution much more than the Tomstown limestone and forms hills in contrast to the limestone valley between them and South Mountain. Within this valley, however, there are long, narrow elevations trending northeast-southwest which owe their origin to syn- clinal infolding of remnants of Waynesboro sandstone. Some of the pro- nounced hills of this valley region, however are underlain by limestone, but these elevations also have resulted from differential resistance to weathering, as they are formed in large part of black banded chert which is a characteristic component of the upper beds of the Tomstown. A good example of a Tomstown limestone valley is the lowland area in which Cavetown is located with a ridge of the Waynesboro formation to the west and the foothills of Harpers shale and South Mountain of Weverton sand- stone on the east.

62 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

Exposures of this limestone are infrequent because its area of outcrop, lying as it does at the foot of South Mountain, commonly is covered by a thick deposit of mountain wash in addition to its own mantle of soil. This mountain wash is thickest and most widely spread where streams from the mountain enter the valley and form alluvial cones. In Mary- land, however, as mentioned above, this Lower Cambrian limestone is often only moderately folded and this, in connection with other factors, causes its area of outcrop to be much wider than in neighboring states. Overturned folds and faults are not uncommon, but as a rule these are of relatively insignificant proportions so that the usual condition of gently dipping strata is soon resumed. Such a fold with slight faulting is well displayed along the Western Maryland Railway, one mile west of Cavetown.

LITHOLOGIC CHARACTERS. — In the type area, southern Pennsylvania, the Tomstown limestone is described as a formation Composed largely of thin bedded and massive dolomite and limestone with considerable shale interbedded near the base. The rocks are not well exposed in Pennsyl- vania and it is possible that the marbles which are such a conspicuous feature of the formation in Maryland are present also in Pennsylvania. At any rate proceeding southward into Maryland the main mass of the formation consists of white to pinkish shaly marble which upon weather- ing gives rise to yellow and greenish shale-like fragments quite sericitic in nature. The Tomstown limestone is especially well exposed in a belt of outcrop three miles in width southeast of Hagerstown, where the usual drift deposits are not so thick and widely dispersed. In this area ex- posures, particularly of the middle and upper beds of the formation, are numerous.

The lowest beds of the Tomstown are not well exposed in Maryland, being nearly everywhere buried beneath the mountain wash. However, it is believed that the gray to dark blue massive, rather pure limestone exposed in the large quarry at Cavetown represents some portion of the lower Tomstown, since at this point the Tomstown is faulted against the Waynesboro and the characteristic marbles are not in evidence. The

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE IV

FlG. I. — EXPOSURE OF TOMSTOWN LIMESTONE ALONG TROLLEY LINE JUST SOUTHEAST OF WAGNERS CROSS ROAD, WASHINGTON COUNTY, MARYLAND, ILLUSTRATING WEATHERING OF MASSIVE SHEARED LIMESTONE INTO SHALE FRAGMENTS.

FlG. 2. — LIMESTONE QUARRY AT CAVETOWN, MARYLAND, SHOWING TOMSTOWN LIMESTONE FAULTED AGAINST WAYNESBORO SANDSTONE.

MARYLAND GEOLOGICAL SURVEY 63

uppermost beds of the formation, on the contrary, are very commonly exposed in Maryland because there are so many small areas of the over- lying Waynesboro formation yet remaining in the valley to mark the top of the Tomstown. These upper strata, while still retaining pinkish to pearl-colored marble beds, also comprise massive dark blue magnesian limestones. Most of the limestones of the Tomstown, and especially the marbles, exhibit some lamination with the result that upon weathering the rock is easily split into thin slate-like fragments. This lamination is usually quite regular, but in southern Maryland there is a body of Toms- town limestone where the rock is so irregularly laminated that it weathers into a mottled effect. Shearing of this laminated limestone is frequent, especially in the marbles. Such strata give the characteristic fracture due to the combination of lamination and shearing.

The shape of the characteristic shale fragments resulting from the weathering of this limestone is due to this same combination of lamination and shearing, so that, while many of the pieces are broken, others are undulated or twisted. The shearing planes are marked on the residual shale-like fragments by thin films of silky, sericite-like material. Some- what similar shale fragments result from the weathering of the Elbrook formation. When the Tomstown and Elbrook limestones are brought in contact by f aulting-out of the intervening Waynesboro formation, careful discrimination is necessary to identify the formations correctly. In doubtful cases it is necessary to search for an outcrop of the rock furnish- ing the shale residue. When this has been found it should be easy to distinguish the sheared marbles of the Tomstown from the dull laminated clayey limestone of the Elbrook.

RESIDUAL PRODUCTS. — One of the characteristic residual products of the Tomstown is black banded chert in small blocky pieces left in the soil upon the weathering of the upper beds of the formation. This chert is almost chalcedonic in nature and the black bands passing through it give it somewhat the aspect of agate. Chert of this particular nature is not found again until the middle division of the Stones Eiver limestone, and as there is little danger of confusing these two widely separated forma-

64 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

tions which are also quite distinct lithologically, the banded chalcedonic chert of the Tomstown can be relied upon as a distinguishing feature as much as a characteristic fossil. The usual fragment of this chert is a block four or five inches long, several inches wide and an inch or two thick. The upper and lower surfaces are uneven and coarsely pitted, but the interior is of dense black and lighter colored silica almost waxy enough to be called chalcedony. This chert in the soil is largely responsible for the maintenance of those hills in the Tomstown limestone valley which are not capped by the Waynesboro formation. The hills southwest of Pondsville are due to the chert of the upper Tomstown.

A second residual product of the Tomstown limestone is the yellow to greenish shale fragments resulting from the weathering of the marbles of the formation. As the black chert occurs only in the upper part of the Tomstown and the shaly marbles occur throughout its thickness, these shale fragments are more widely dispersed than the chert and therefore may be said to be more characteristic of the formation as a whole. The decay of the shaly marbles into yellow and greenish shales is well dis- played in the cut of the Hagerstown-Frederick trolley road just east of Wagner's Cross Roads. At the bottom of the cut the rocks are massive limestones, although much sheared. Near the top, solution has removed much of the lime and the strata are easily broken into shaly blocks. At the surface itself the separation into shale fragments is complete, each fragment being covered with a soapstone-like film, in many cases not unlike sericite.

ECONOMIC FEATURES. — The decomposition of the Tomstown limestone results in a firm, compact soil, but over most of the area this soil has been lightened and made more porous by admixture with the sand and gravel from the nearby mountains. This is particularly true on the lower slopes of South Mountain where the orchards of the famous South Mountain peach belt are to a great extent located on such well-drained soil.

In the past, kilns for the burning of agricultural lime were numerous in the Tomstown area, but this practice has now been discontinued. At present the only quarry of consequence where the Tomstown limestone is

MARYLAND GEOLOGICAL SURVEY

FlG. I. — VALLEY OF TOMSTOWN LIMESTONE LOOKING EAST FROM CAVETOWN, MARYLAND, SHOWING FOOTHILLS OF HARPERS SHALE, AND SOUTH MOUNTAIN OF WEVERTON SANDSTONE IN THE DISTANCE.

FlG. 2. — VALLEY OF TOMSTOWN LIMESTONE WITH SOUTH MOUNTAIN IN THE DISTANCE SHOWING PENEPLAINED SURFACE. THE HILL JUST BEYOND THE HOUSE IS CAPPED BY TOMSTOWN CHERT. PHOTOGRAPH TAKEN ONE MILE SOUTH OF CAVETOWN, MARYLAND.

MARYLAND GEOLOGICAL SURVEY -65

utilized for lime and ballast is at Cavetown, where good location and transportation facilities are at hand.

The marbles of the Tomstown were formerly quarried to a considerable extent, especially in the southern part of the area, but at present the only development is near Eakles Mills. White marbles which occur at several horizons in the formation, have been most frequently quarried. With these is a bed of a cream-white color with a very fine texture, but the associated beds are impure and have the more usual grayish banded appearance. The pinkish shaly marbles likewise include some pure white beds which might be profitably quarried if transportation facilities were available. An abandoned quarry, situated on the bank of Beaver Creek, one mile northeast of Harmony Hill school, gives a good exposure of these light colored marbles.

AREAL DISTRIBUTION. — The outcrops of the Tomstown limestone are confined to the eastern part of the Hagerstown Valley just west of the Blue Eidge in a belt of low land at the foot of South Mountain about two miles wide in the northernmost portion, increasing to a width of three miles or more southward. Along the entire eastern border of the forma- tion the Harpers shale is faulted against this limestone with the inter- vening formation, the Antietam sandstone, either wanting or outcropping some little distance east of the Tomstown as an infold in the shale. The western border of the Tomstown limestone in northern Maryland as far south as the Western Maryland Eailway is the normally overlying Waynesboro formation. South of this, the Tomstown is faulted first against the Elbrook formation, then against the Conococheague limestone as at Chewsville, then against the Elbrook again for some miles, and finally at Benevola on the National pike, the succession becomes normal again. A fault passing north and south just east of Boonsboro parallels South Mountain and along its western side several small areas of Waynes- boro are exposed. West of this fault in the middle of the Tomstown valley the line of hills starting a mile north of Smithsburg and ending near Beaver Creek are formed by an infolded area of the Waynesboro formation. With these exceptions and several small areas where the

G6 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND

Waynesboro formation is nothing but a surface remnant, all the valley east of the line first mentioned is composed of the Tomstown limestone.

THICKNESS.— In spite of numerous good exposures, no continuous sec- tions of any thickness of the Tomstown limestone are exposed in Mary- land, and indeed no place has been found where the normal sequence can be determined. In southern Pennsylvania an approximate thickness of 1000 feet has been measured. This has been accepted as the thickness in Maryland, although in the southern half of the state where the marbles are well developed a greater thickness is possible.

AGE AND CORRELATION. — No fossils have so far been noted in the Tomstown limestone in Maryland and indeed the sheared marbles and dolomitic strata of the formation are not favorable for the occurrence of organic remains. In southern Pennsylvania near Roadside and near Waynesboro, fragments of the mollusk shell Salterella have been collected. A few miles north of this at the foot of the mountain east of Little Antietam Creek fragments of the characteristic Lower Cambrian trilobite Olenellus were discovered by Walcott. A Lower Cambrian age for the formation is therefore accepted, although the paleontological evidence is still quite meager. Fossil evidence in the rocks holding the same strati- graphic position in states to the south is also very slight, but favors the same age. The most interesting of these fossils is a large species of Archeocyathus recently found in the Sherwood limestone and a similar large species of the same genus in the Shady limestone.

In contrast with the few fossils of the areas just mentioned is the abundant, well-preserved Lower Cambrian fauna found in limestones and shales in the vicinity of York and Fruitville, Pennsylvania. It seems probable that these f ossilif erous strata form a part of the Tomstown limestone, but the lithology is so different that a close study of the inter- vening area is necessary before this correlation can be made with certainty.

THE WAYNESBORO FORMATION

Viewed as a lithologic unit the most obvious and easily recognized formation in the Shenandoah limestone series is the mass of reddish to purple calcareous sandstone and shale here known as the Waynesboro

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE VI

FlG. I.— OVERTURNED FOLD WITH SLIGHT FAULTING IN TOMSTOWN LIMESTONE ALONG WESTERN MARYLAND RAILWAY, ONE MILE WEST OF CAVETOWN, MARYLAND.

FlG. 2. — RIDGE OF THE WAYNESBORO FORMATION JUST EAST OF MIDDLE BRIDGE, ANTIETAM BATTLEFIELD, WASHINGTON COUNTY, MARYLAND.

67

formation. These striking beds form more or less conspicuous ranges of hills in the lowland area just west of the Blue Ridge and corresponding mountain ranges to the north and south of Maryland. Weathering of these red to purple strata results in similarly colored soils which there- fore contrast strongly with the grayish-brown and black soils of adjacent limestone areas.

NAME AND SYNONYMY. — In publications upon the central and northern part of the Appalachian Valley the red zone mentioned above was fre- quently noted, especially in folios of the United States Geological Survey, but it was not separated as a distinct formation until 1905 * when H. D. Campbell proposed the name Buena Vista shale for corresponding red beds in central western Virginia. Later Stose 2 discriminated similar sandstones and shales in southern Pennsylvania as the Waynesboro forma- tion, the typical development of which extends southwestward from Waynesboro, Pennsylvania, into Maryland, where its outcrops form the " peach lands " in the valley west of the Blue Eidge slope. The formation here being the same in general character and sequence of beds as in Pennsylvania it is manifestly desirable to use the same name for it in both states. It is not yet finally decided whether this name should be the one proposed by Stose or some other. Regarding the term, Buena Vista, it cannot be used in this connection because the same name had been given many years before to rocks in Ohio. Among several probably synonymous terms that have been considered, the name Wautaga shale, proposed in 1903 by Keith,3 for series of red and green shales' in east Tennessee, occu- pying apparently the same stratigraphic position as the Maryland forma- tion under consideration, is perhaps the most appropriate designation. According to Keith the Wautaga shale has been traced far enough north- ward to warrant the application of this rame in west central Virginia in place of the preoccupied term Buena Vista; and there may be sufficient reason for its extension to Maryland and southern Pennsylvania. How- ever, the lithologic development of this northern f acies of the Appalachian

1Amer. Jour. Sci., vol. xx, 1905, pp. 445-447.

2 Folio 170, U. S. Geol. Surv., 1910.

3 Cranberry folio, No. 90, U. S. Geological Survey, 1903.

68 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

Middle Cambrian red beds for which the term Waynesboro was proposed, is different from the Wautaga facies to the south in that considerable thicknesses of sandstone and limestone are intercalated with the char- acteristic-red and purple shales. Moreover, there are two other names whose claims must be considered before this nomenclatural question can be finally settled. These names are the Eome sandstone and shale and Eussell shale, both in good standing and of prior dates than Wautaga shale. Provisionally, therefore, it is thought advisable to retain the name Waynesboro formation for these strata in Maryland and Pennsylvania.

LITHOLOGIC CHARACTER AND THICKNESS. — In Maryland as well as in the type area of outcrop, the Waynesboro formation consists of a lower member of very siliceous gray limestone and calcareous sandstone, a middle member of limestone, and an upper one of red and purple siliceous shale, aggregating 1000 feet in thickness. Of the three members, the upper is the best developed and most frequently exposed, since faulting often cuts out the middle limestone and lower sandstone divisions. The weathering of this upper part is mainly responsible for the characteristic- red color of the soils derived from the formation. The basal siliceous limestones weather into shaly, porous sandstone with which are associated numerous blocks of secondary white vein quartz and rounded corrugated sandy fragments full of crevices lined with small quartz crystals. The limestones of the middle division range from dark blue massive limestone to fine grained white marble which, on account of their soluble nature, are generally not exposed. In Pennsylvania this middle portion is several hundred feet thick, but in Maryland the thickness is probably not as great. These limestones become siliceous toward the top of the member and finally seem to grade into the dark red to purple sandy shale which makes the upper part of the formation. Certain parts of the upper mem- ber contain argillaceous flaggy sandstone which has been locally quarried for paving stones. On weathered surfaces the flags break up into frag- ments of sandy shale.

Such slabs frequently exhibit ripple marks and mud cracks, the latter being well displayed in some of the paving stones of Smithsburg. One

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND GflDOVJtJIAN,

IRON-STAINED CONTORTED SANDSTONE OF WAYNESBORO FORMATION. THE UPPER FIGURE REPRESENTS THE USUAL ASPECT OF THE ROCK. THE CAVITIES IN THE SANDSTONE ARE COVERED BY DRUSY QUARTZ AS SHOWN IN THE FIGURE TO THE LEFT (X 2) OR BY BEAUTIFUL MINUTE CRYSTALS OF QUARTZ ILLUSTRATED IN FIGURE TO RIGHT (X 6).

MARYLAND GEOLOGICAL SURVEY 69

of these showed the interesting occurrence of two sets of intersecting mud cracks, one set about a foot apart and the other about four inches.

TOPOGRAPHIC FORM. — Faulting is so frequent along the eastern edge of the Waynesboro outcrops in Maryland that the normal sequence of strata is seldom apparent. Siliceous strata always form a part of the Waynesboro wherever developed, so that its topographic form is always an elevated area. If the strata have been strongly folded this highland area assumes the form of elongated hills paralleling South Mountain. Should the normal sequence of the three divisions of the Waynesboro occur, the basal siliceous strata will give rise to a range of low hills nearest the mountain and the upper sandy shales will occasion another range to the west, the narrow depression between them being underlain by the less resistant limestones of the middle portion.

TOMSTOWN-WAYNESBORO BOUNDARY. — The base of the Waynesboro formation is formed of a very siliceous gray limestone which weathers to slabby, porous sandstone. Except in very fresh exposures the limestone nature of this part of the formation is not apparent and it seems to be made up of sandstone entirely. Sandstone slabs are very abundant on the weathered slopes and associated with them are large masses of contorted, minutely laminated, iron stained, sandy rocks, with numerous cavities filled with beautiful drusy quartz. These masses are sometimes several feet in diameter and their presence in the fields and especially in the fences identifies this basal portion of the Waynesboro. Wherever in Maryland the Waynesboro sequence is normal such iron stained, drusy quartz masses are found in abundance. Associated with this sandy rock and also in the higher strata of the lower portion of the Waynesboro are numerous fragments of secondary white vein quartz which in connection with the other siliceous rock helps in identifying the basal beds. Plate VII represents a small fragment of the contorted sandy masses in which all the crevices are filled with minute quartz crystals. An enlarged view of a drusy quartz portion of one of these masses is shown on the same plate. The crystals, though perfectly formed, are so small as to be indistinguishable without a magnifying lens. To the unaided eye the

70 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

surface of this drusy quartz has a beautiful velvety appearance, the beauty of which is enhanced by the lemon-yellow to brownish-olive color with just enough reflection from the minute crystals to add a silvery sheen to the surface. Other specimens of the same rock show these crystals increased to a length of about 2 mm. and a magnified view exhibits their perfection of form. These crystals are interesting in that practically all of those observed are terminated by a single rhombohedron instead of the two usually found in quartz.

AREAL DISTRIBUTION. — The geologic structure of the various occur- rences of the Waynesboro formation in Maryland varies considerably. The normal section from upper Tomstown through the Waynesboro into the overlying Elbrook is present only in the strip of outcrops extending from Benevola southwest to Burnside Bridge east of Sharpsburg, and even here both ends of the strip are faulted. The ridge east of the Upper Bridge and Middle Bridge of the Antietam battle-field exposes the different divisions of the formation to best advantage for study. Here only does the limestone middle portion form its characteristic topographic feature of a valley between the two ridges left by the lower and upper siliceous parts. Northeast of Benevola is a number of small outcrops which in most cases are little more than surface remnants. The same holds true of several lines of outcrop east of Chewsville where the rocks are of such little depth that the underlying limestone is occasionally plowed up in the fields. A shallow syncline commences one and a half miles north of Smithsburg and terminates seven miles to the southwest near Beaver Creek, one mile northeast of Wagner's Cross Eoads, in another normal syncline. These two syncline terminal areas are connected by a narrow strip of the formation in which the greater part of its thickness is covered by overthrust faulting. Thus in the limestone quarry at Cave- town the lower part of the Tomstown limestone is faulted against the purple shales of the Waynesboro. An interesting anticline of Waynesboro sandstone exposing the upper Tomstown with its characteristic black banded chalcedonic chert in its axial part, enters the state from Pennsyl- vania and is terminated by faulting at Ringgold.

MARYLAND GEOLOGICAL SURVEY 71

On the western edge of the Valley the Waynesboro outcrops in a narrow strip along the eastern base of Fairview and Powell mountains, where it is brought to the surface by faulting. Few outcrops can be found in this area, however, since the country is so thoroughly covered with drift material from the nearby mountains.

ECONOMIC FEATURES. — Compared with the neighboring limestone areas the soils derived from the weathering of the Waynesboro formation are comparatively poor and the fields are frequently covered with small sandstone or sandy purple shale slabs and milky quartz fragments. Freshly plowed fields, especially when wet, have a distinct purple to red color. As the formation always outcrops topographically above the adjoining areas, and as the soil is quite porous, Waynesboro areas have both good water and air drainage. This causes such areas to be of especial value for fruit culture, and as a result most of the Waynesboro hills have been cleared and planted in orchards, peaches being the fruit most commonly raised.

From a commercial standpoint the Waynesboro formation is of little importance. When there was a strong local demand for iron .years ago, it afforded small quantities of residual iron ore. The limestones in the middle portion have in the past been employed very locally for lime burn- ing. The thin-bedded sandstones make excellent flagging stones which are used in the villages close to the areas of outcrop. Mention of the suncracked flagstones in the pavements of Smithsburg has been made in a preceding paragraph.

AGE AND CORRELATION. — No fossils have been observed in the Waynes- boro formation in Maryland, but at the type locality just north of the Maryland line a few poorly preserved phosphatic brachiopods of the genus Lingulella have been noted. These suggest a Middle Cambrian age. The Buena Vista shale of Virginia has yielded an Olenellus-likQ trilobite which would suggest a Lower Cambrian age for this shale, although in recent years the range of Olenellus has been extended into the Middle Cambrian. The age of the Waynesboro is therefore not clearly indicated by paleontologic evidence, but stratigraphic and diastrophic data place it as Middle Cambrian.

72 THE CAMBRIAN AXD ORDOVICIAX DEPOSITS OF MARYLAND

THE ELBROOK FORMATION

Overlying the purple shales of the Waynesboro formation in the normal section is a thick series of light-blue and gray shaly limestone and calcareous shales which, in Maryland, are seldom exposed in natural outcrops. These strata were not recognized as a distinct formation until 1910, when Stose1 named them the Elbrook formation from the village on the Western Maryland Railway in southern Pennsylvania.

LITHOLOGIC CHARACTER AND THICKNESS. — The shaly limestone and calcareous shale making up the major portion of the Elbrook formation weathers very rapidly into shale fragments, so that usually there are few natural outcrops. In stream valleys and artificial exposures the following general succession has been determined. At the very base of the formation are beds of rather pure dark blue massive limestones not over 100 feet thick which have afforded the only fossils found. Succeeding this and constituting approximately the lower third of the formation is 1000 or more feet of minutely laminated shaly limestone and calcareous yellow to green and some reddish shale which weathers into calcareous shaly plates. The middle of the formation is marked by siliceous limestones and massive beds of dolomite which form a slight elevation in the gen- erally low area of outcrop of the formation. The upper half of the formation is composed of light colored calcareous shale and impure laminated limestones which, like the lower part, weather shaly. How- ever, it is slightly more siliceous than the lower third and weathers into more irregular often cubical sandy red to brownish fragments. It is followed by the limestone conglomerates and sandy oolite marking the base of the succeeding Conococheague limestone. The total thickness of the Elbrook as determined in both northern and southern Maryland is about 3000 feet.

AREAL DISTRIBUTION. — Notwithstanding its great thickness the Elbrook formation occupies less area in Maryland than almost any other of the Cambrian or Ordovician formations. It appears at the surface in a narrow northeast-southwest band crossing the state in the .eastern part

1 Folio 170, U. S. Geol. Surv.

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE VIII

FIG. i. — EXPOSURE OF ELBROOK LIMESTONE ALONG BALTIMORE AND OHIO RAILROAD JUST

SOUTH OF SHARMAN, MARYLAND. THESE MASSIVE BEDS WEATHER INTO THIN SHALY LAYERS.

FlG. 2. — VIEW LOOKING NORTH OVER ANTIETAM BATTLEFIELD SHOWING EXPOSURE OF ELBROOK LIMESTONE. PHOTOGRAPH TAKEN ONE-HALF MILE EAST OF SHARPSBURG, ALONG ROAD TO BURNSIDE BRIDGE, MARYLAND.

MARYLAND GEOLOGICAL SURVEY 73

of the Hagerstown Valley and in a still narrower band along the extreme western edge of the Great Valley. The eastern area of outcrop enters the state from Pennsylvania just north of Ringgold and proceeding south- ward in a strip less than a mile in width is terminated by a fault near Qhewsville. South of Chewsville the throw of this fault becomes less, so that the Elbrook formation reappears at the surface and continues south- ward in a band averaging a mile in width paralleling the hills of the Waynesboro formation on the east. At Sharpsburg beyond the extremity of an infolded mass of the overlying limestone, the Elbrook is partly repeated in the two limbs of the syncline and the outcrop correspondingly widened.

The western band of outcrop doubtless parallels North Mountain, hut is known only from a few exposures, as almost its entire area is covered by mountain wash. The beds dip steeply in these exposures, so that the outcrop of the formation must be confined to a strip scarcely exceeding a half mile in width.

TOPOGRAPHIC FORM AND RESIDUAL PRODUCTS. — Where the geologic section is normally developed, two ranges of pronounced hills — those of the siliceous Waynesboro on the east, those of the siliceous limestones of the Conococheague on the west — flank a lowland in which the less resistant limestones and shales of the Elbrook are at the surface. However, this lowland band is not a simple valley, but is divided longitudinally into two narrow valleys by a series of low hills due to the relatively resistant beds of siliceous limestone and dolomite that occur in the middle part of the Elbrook.

The topographic form of the Elbrook is not unlike that of the Toms- town and the shale fragments left in the soil from both formations arc quite similar. In areas where the intervening Waynesboro formation is cut out by faulting, such as the area about five miles southeast of Hagers- town, great care must be exercised in discriminating the two formations. Determined search in areas of Tomstown limestone will sooner or later reveal outcrops of the characteristic sheared marble which on weathering leave the shale-like residual fragments. On the other hand, in an Elbrook

74 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

area the simulating residual shale will be traced to merely dull laminated limestone or calcareous shale.

A characteristic weathering product of the lower half of the Elbrook is light colored, sometimes almost white, waxy translucent chert approach- ing chalcedony in appearance and structure. This appears in the soil in small fragments, usually only a few inches thick with more or less rounded edges. The color of this chert is sometimes a light yellow or even light red, but it is never black nor banded like the Tomstown chalcedonic chert.

AGE AND CORRELATION. — Fossils have been found only in the basal limestones of the formation in the vicinity of Waynesboro, Pennsylvania. These consist mainly of well-preserved heads and tails of two species of trilobites, one of which, a species of Dolichometopus, is not uncommon. These trilobites belong to new species whose age relations have not been definitely determined. However, as they are closely allied to species known to be characteristic Middle Cambrian fossils it seems highly prob- able that the Elbrook is of similar age.

THE CONOCOCHEAGUE LIMESTONE

On the northwest, north and east flanks of the Adirondack uplift the Potsdam sandstone grades upward through passage beds into a limestone to which Ulrich and Gushing have applied the name Hoyt limestone. This is succeeded by a massive dolomite known as the Little Falls dolo- mite. Fossils have been found in all three of these formations, but are reasonably plentiful only in the Hoyt limestone. The fauna of this limestone was first procured and in part briefly described by Walcott many years ago. Recently the same authority revised and completed his studies of the Hoyt and Potsdam faunas, the results being published in a small monograph. As now known these early New York " Saratogan " faunules comprise, besides a number of trilobites and shells of various kinds, large concentrically laminated masses in reef -like aggregations. These masses are thought to be calcareous algae. Two species are dis- tinguished, one having been described by Hall under the name Cryptozoon proliferumj the other is a related new species. These two species have

76 THE CAMBRIAN AND OEDOVICIAN DEPOSITS OF MARYLAND

an important bearing on the age determination of certain formations in the Appalachian Valley. Apparently the same species occur abundantly in the basal part of the Kittatinny limestone in the Lehigh Valley of Pennsylvania and nearby areas in New Jersey where they are associated with trilobites of the same general types as those found near Saratoga, New York.

In the Cumberland Valley of southern Pennsylvania these same species of Cryptozoon are found in the basal part of a, thick series of siliceous banded limestone that lies between the Middle Cambrian Elbrook lime- stone and another great mass of relatively pure limestone that corresponds to the well-known Beekmantown limestone of the New York section. This intervening formation which is about to be described was dis- tinguished and mapped by Stose in the Mercersbutrg-Chambersburg (Pennsylvania) folio of the U. S. Geological Survey as the Conococheague limestone, so called from the good exposures along the banks of Conoco- cheague Creek near Scotland, Pennsylvania. From this place the forma- tion extends in typical development to the Great Valley of Western Mary- land, where its outcrops cover a considerable area.

LITHOLOGIC CHARACTERS. — The main body of the Conococheague lime- stone is composed essentially of massive dark-blue, closely banded lime- stones. The banding is usually one-half to one inch in width and is caused by the alternation of thin, wavy, sandy laminae with thin layers of purer rock. The sandy laminae are inconspicuous in the freshly fractured rock, although close examination reveals the alternation of the dark blue purer and gray siliceous limestone bands quite clearly. Upon weathering, the siliceous laminae appear as yellowish sandy streaks separating light-blue or gray bands of limestone. Further weathering causes the siliceous laminae to stand out in relief as more or less parallel ribs. Finally, where the rock has suffered complete disin- tegration, these laminae are left in the soil as hard, siliceous thin plates. Strata of this nature can be found in almost any outcrop of the formation, but interbedded with them are various other types of limestone. Of these, the most striking are the beds of " edgewise " conglomerate which alter- nate frequently with the usual banded limestone. This conglomerate is

MARYLAND GEOLOGICAL SURVEY

FlG. I. — CRYPTOZOON REEF AT BASE OF CONOCOCHEAGUE FORMATION, EXPOSED ALONG NORFOLK AND WESTERN RAILROAD ABOUT ONE MILE SOUTHWEST OF ANTIETAM STA- TION, MARYLAND, PHOTOGRAPH ABOUT ONE-FIFTEENTH NATURAL SIZE.

FlG. 2.— CRYPTOZOON STRUCTURE IN UPPER PART OF CONOCOCHEAGUE LIMESTONE EXPOSED ALONG WESTERN MARYLAND RAILWAY, ONE-FOURTH MILE WEST OF CHARLTON MARYLAND PHOTOGRAPH ONE-SIXTH NATURAL SIZE. THE OOLITES HAVE BEEN OUTLINED IN' INK

MARYLAND GEOLOGICAL SURVEY 77

composed of slender fragments of limestone tilted at all angles in a matrix of limestone distinctly different in composition.

The general nature of the strata composing the Conococheague lime- stone is shown in the type section near Scotland, Pennsylvania, published by Stose. The continuity of this section is known to be interrupted by small faults and folds. Although allowances were made for these, the section, as finally compiled, is scarcely to be considered as entirely satis- factory. The total thickness may be greater than given.

Section of Conococheague Limestone West of Scotland, Pennsylvania

Feet

Rather pure light-colored limestone, much sheared, followed above by siliceous banded dark limestone and " edgewise " conglomerate (Stonehenge member of Beekmantown). Granular limestone with coarse " edgewise " conglomerate, oolite, and

fine-grained pink marble, with numerous slaty partings 90

Covered .- . . . 300

Pure dove-colored even-grained limestone interbedded with light siliceous-grained cross-bedded limestone, coarse " edgewise " con- glomerate, and chert 15

Largly covered : dark impure limestone with large banded chert at the

base 390

Dark and light limestone, in part banded with impurities 10

Dark, rather impure limestone with argillaceous partings weathering to slaty fragments and soft yellow shale; contains trilobites and

beds of oolite 180

Dark limestone with shaly partings on weathering 90

Massive beds of light, dense, even-grained limestone with few wavy

siliceous partings weathering in relief 40

Covered 70

Wavy impure siliceous banded limestone, weathering hackly and shaly. 180

Dense black impure limestone, weathering with thick gray coating 30

Thick massive beds of crumpled siliceous banded limestone 40

Section folded and discontinuous. Dense siliceous banded limestone, with sandy beds, oolite, " edgewise " conglomerate, and layers of Cryptozoon at the base ' 200±

1635±

The exposures of the Conococheague limestone in Maryland are too discontinuous to allow a complete section to be taken at any particular locality. The following general section gives the sequence of these rocks east of the Martinsburg shale belt of the Valley.

78 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

General Section of the Conococheague Limestone in the Hagerstown Valley, Maryland

Feet

Massive, rather pure, light colored limestone with cephalopoda and gastro- pods of the Stonehenge limestone.

Pink marbles, oolite, granular limestone with edgewise conglomerate and massive fine grained light colored limestone separated by beds of banded dark blue siliceous limestone. Vein quartz with crystals and yellow chert are left in soil upon weathering 400

Dark impure banded limestone weathering to slaty fragments and banded

chert. Occasional beds of edgewise conglomerate 600

Wavy, blue to black siliceous banded impure limestone with layers of

edgewise conglomerate 400

Siliceous banded dark blue limestone with intercalcated sandy beds, oolite and edgewise conglomerate. On weathering some of the strata give

rise to large chunks of scoriaceous chert 200

'Massive dark blue to light colored rather pure limestone with reefs of

Cryptozoon proliferum Hall and C. undulatum new species 50

Light colored calcareous shale and laminated impure limestone of the Elbrook formation, weathering shaly.

Total 1650

Because of the discontinuous exposure of the formation and the folding to which it has been subjected the thickness is a difficult matter to deter- mine. The above total of 1650 feet is apparently a fair average for Maryland.

Although five divisions are shown above in the general section of the Conococheague limestone, the rocks may be conveniently grouped for purposes of study into three divisions. First, a basal division of 250 feet of oolite, edgewise conglomerate and Cryptozoon reefs; second, the main mass of the formation about 1000 feet or more in thickness made up of the usual banded limestone; and third, an upper part of 400 feet which con- tains pink marbles in addition to the usual rocks of the formation. All three divisions are indicative of shallow water conditions during their deposition, but the basal beds are particularly so. The edgewise con- glomerate and the oolites are shallow water deposits and the rounded grains of quartz occurring with them indicate nearby land. In these beds are also inclusions of red clay which closely resemble clays resulting from the surface weathering of limestone. The most interesting residual

80 THE CAMBRIAN AND OKDOVICIAN DEPOSITS OF MARYLAND

product of these basal beds is a scoriaceous chert which occurs in great quantity in the soils derived from their weathering. These chert masses are sometimes several feet in diameter, and while they are composed of crystalline milky quartz, they are so iron stained and cavernous that they have the appearance of slag or volcanic material. Fences composed of this chert are not uncommon in both the northern and southern areas of outcrops and they are good evidence that the dividing line between the Elbrook and Conococheague formations is close at hand. Good examples of such fences may be seen on the Antietam battle-field just north of Sharpsburg along the Hagerstown turnpike.

The main mass of the formation is described in preceding paragraphs. The upper beds of pink marble are very much like similar strata in the overlying Beekmantown limestone. However, there is no occasion to confuse the two since the usual siliceous banded rocks of the Conoco- cheague are intercalated with these purer strata. Besides, the soils derived from these upper beds contain abundant fragments of black to yellow chert and milky vein quartz. Such siliceous residuals are char- acteristic of the Conococheague, but not of any part of the Beekmantown.

The above remarks apply particularly to the formation as developed east of the Massanutten syncline. West of the great shale belt in Mary- land the general features of this limestone remain about the same, with the exception that 600 or more feet of massive sandy dolomite are inter- calated between the usual sandy laminated limestones and the overlying Beekmantown limestone. These sandy dolomites weather into sandstones which strew the ground with large and small blocks. These sandstones are coherent enough at times to have been used in the past as a local source of grindstones. More extended study in neighboring states will probably show that these upper sandy dolomites represent the eastward extension of strata which do not really belong with the typical Conoco- cheague limestone. However, until such studies have been made it is thought advisable to classify these upper sandy beds provisionally with the Conococheague limestone. A good section of this upper member may be seen in the Western Maryland Railway cut just west of Charlton,

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE X

FlG. I. — EXPOSURE OF CONOCOCHEAGUE LIMESTONE ON EDGE, ALONG ROAD NEAR BAKERS- VILLE, MARYLAND. THE CHARACTERISTIC STRONGLY CRINKLED, SANDY LAMINAE ARE WELL DEVELOPED.

PlG. 2. — LOWER CONOCOCHEAGUE SCORIACEOUS CHERT EXPOSED IN FENCE ALONG HAGERS- TOWN TURNPIKE JUST NORTH OF SHARPSBURG, MARYLAND.

MARYLAND GEOLOGICAL SURVEY 81

Maryland. East of the Massanutten syncline these sandy strata are known only in the western part of the broad expanse of Conococheague limestone south of Hagerstown.

TOPOGRAPHY. — The topographic features of the Conococheague lime- stone are not as distinctive as those of the adjacent formations, still its presence is indicated by relatively minor topographic pecularities that after all are decidedly characteristic. The siliceous beds at the base of the formation are most resistant to weathering and as a result give rise to a line of low hills trending in the direction of the outcrops. The considerable amount of scoriaceous chert arising from the weathering of these lower beds also tends to form highlands. The hills formed by the siliceous basal beds are most conspicuous in the northeastern part of the valley in Maryland from the state line southeast through Bowman's Mill to Chewsville. The siliceous character of the upper portion of this forma- tion likewise resists weathering, but not in as great a degree as the lower division. In general the areas of Conococheague limestone are somewhat elevated and exhibit rugged topography in comparison with the adjoining formations. Outcrops of the limestone are numerous, in fact foiling country with low hills and numerous rocky exposures is its characteristic feature in northern Maryland, but in the broad area in the southern part of the state the rocks themselves are seldom seen. Here the land is well cultivated and all evidence of the outcrop has usually been removed. The stone fences, however, are indicative of the underlying formation, as the rock employed in them has usually been taken from neighboring fields. Stone fences built of the characteristically banded Conococheague lime- stone are a sure indication of the presence of the formation.

AREAL DISTRIBUTION. — The Conococheague limestone forms the sur- face rock of a comparatively broad area in the eastern half of the Great Valley in Maryland, little interrupted by infolds of other formations. This is bordered on the east by the older Elbrook formation, the line of contact being quite regular except in the northern part of the state where faulting brings two narrow tongues of the Elbrook to the surface. The western boundary of this area is less regular due to several infolds of the

82 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

Stonehenge member of the overlying Beekmantown limestone. This area of outcrop therefore has a general monoclinal structure since younger beds border it on the west and older beds pass beneath it on the east. East of Hagerstown, Security on the west and Chewsville on the east mark the boundaries of the outcrop which averages three miles in width. Numerous exposures of the typical limestone may be seen along the Western Maryland Eailway between Chewsville and Security and at the latter place the large quarry of the Security Cement and Lime Company exhibits a considerable section of the upper beds (see pi. XII, fig. I). Leitersburg, five miles northeast, stands on a rocky ridge of Conoco- cheague limestone, the rock here belonging to the lowest beds as evidenced by the scoriaceous chert found in abundance in the vicinity. South of Hagerstown the width of the belt of outcrop increases to over five miles, and a wide, unbroken expanse of this limestone occurs along the Potomac and for some miles northward. In many places here the beds are either very gently folded or almost horizontal.

In the western half of the Valley the outcrops of the Conococheague consist of several narrow belts of strata brought to the surface in the lowland area between the shale highland on the east and the front range of the Alleghenies on the west. Here the areas of outcrop are marked by many chert fragments and sandstone debris left in the soil.

AGE AND COERELATION. — Only a small number of species of fossils has so far been discovered in the Conococheague limestone, these consisting of calcareous algae occurring in the basal beds; several brachiopods and trilobites found in the upper strata, and a large species of alga near the top of the formation.- The two calcareous algae (Cryptozoon proliferum Hall and C. undulatum new species) at the base of the formation are found in abundance wherever these beds are exposed. The large Crypto- zoon near the top is a not uncommon fossil, but the trilobite, Saukia stosei Walcott, and the brachiopod, Eoorthis cf. desmopleura (Meek), are of very rare occurrence in the higher beds. The trilobite has been found only in the Cumberland Valley, so it is of little value for exact correlation. Still it belongs to a genus that is elsewhere represented only in late Upper

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE XI

"EDGEWISE BEDS" CHARACTERISTIC OF BEEKMANTOWN (UPPER RIGHT HAND FIGURE) AND CONOCOCHEAGUE FORMATIONS (LOWER FIGURE), HAGERSTOWN VALLEY, WASHINGTON COUNTY. THE UPPER LEFT HAND FIGURE REPRESENTS THE CHARAC- TERISTIC FINELY LAMINATED FEATURE OF THE BEEKMANTOWN LIMESTONE.

MARYLAND GEOLOGICAL SURVEY 83

Cambrian and Middle Ozarkian formations. Moreover, its affinities lie nea-rer the Ozarkian species than the Cambrian, so that its evidence, so far as it goes, favors assignment of the Conococheague to the Lower Ozarkian. Vhe brachiopod, also, as now understood, has too wide a range for detailed stratigraphic work. The two species of Cryptozoon at the base occupy this position throughout a large part of the Appalachian Valley and serve as excellent guide fossils.

The Maryland early Paleozoic section is far from complete and the age of the Conococheague limestone must be determined from more fully developed sections in other areas. The Cryptozoon fauna occurs in central Pennsylvania in the Gatesburg dolomite which, roughly speaking, is the equivalent of the Conococheague limestone. Beneath the Gatesburg dolo- mite, and separating it from the Middle Cambrian, Elbrook, is an Upper Cambrian formation, the Warrior limestone. To the south in Virginia, Tennessee, and Alabama, the same Cryptozoon fauna is also known and in each case it is separated from the Middle Cambrian equivalents of the Elbrook limestone by Upper Cambrian formations of great thickness and containing well-developed faunas. Evidently then we must conclude that the contact between the Elbrook and Conococheague in Maryland is unconformable and represents a stratigraphic break of considerable magnitude.

Cryptozoon Reefs.

The basal 15 or 20 feet of the Conococheague limestone usually exhibit layers so uniformly and curiously laminated over considerable areas that this phenomenon cannot be attributed to ordinary plications in the strata. All of the sandy laminated and banded portions of the formation show a wavy or crinkled structure, especially where strong folding has occurred, but the laminations of the basal beds are of a quite different nature. The limestones in which the latter laminated structures occur are not of the usual banded type, but are composed of a massive, rather homogeneous and somewhat purer rock. In an edge view of a stratum the rock is seen to be made up of thin, parallel films of material piled one upon the other.

84 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

At first these films are practically horizontal to the bedding planes, but soon undulation commences and narrow or broad folds with narrower or sharper bending down of the films occurs. After an interval of several inches exhibiting such undulation, the horizontal lamination is resumed and this in turn is followed by a repetition of the undulations. These wavy outlines as seen in cross-sections of the strata appear as concen- trically lined areas of varying diameter on the bedding planes themselves. The greater the width of the fold seen in transverse section, the greater the diameter of the corresponding concentric area.

These laminated strata at the base of the Conococheague follow two distinct patterns. In each the basal laminae are horizontal to the bedding plane, but the succeeding undulations are quite different. In one kind the undulations are an inch or less across and retain this diameter uniformly. In the other, the width of the undulations varies from a central one, several inches across to lateral ones an inch or less wide. Upon the weathering of the surrounding strata, masses of this laminated rock are left in the soil, still retaining their calcareous composition or, as is more frequently the case, changed to silica. In either case the uni- formity in shape of these residual masses would seem to indicate that they are definite organic structures.

Walcott has described a number of quite similar laminated structures from the Proterozoic rocks of the West and has shown that they represent the secretions of calcareous algae. Certain of the Proterozoic limestones contain beds crowded with these algal structures which are repeated again and again through thousands of feet of strata. These remains are not those of the fossil plant itself, but are simply the secretions of calcium carbonate upon the tissue of the plant. As is well known, calcium carbonate held in solution by an excess of carbon dioxide in the water is deposited when the carbon dioxide is abstracted. In securing carbon from the carbon dioxide for the building of their tissues the lime is deposited upon the films of the plant which abstracts the carbon dioxide. The form of the plant, however, is well preserved in these limestone secretions.

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE XII

FlG. I. — QUARRY IN UPPER PART OF CONOCOCHEAGUE LIMESTONE WITH SECURITY CEMENT WORKS, SECURITY, MARYLAND, IN DISTANCE.

FlG. 2. — TYPICAL EXPOSURE OF THE LOWER PURE FINELY CONGLOMERATIC BEDS OF THE STONEHENGE LIMESTONE ALONG NATIONAL HIGHWAY, JUST SOUTH OF FUNKSTOWN, MARYLAND.

MARYLAND GEOLOGICAL SURVEY 85

The Proterozoic forms of calcareous algae have been described under six genera, but all of the Cambrian and Early Ordovician forms have been referred to the single genus Cryptozoon. The basal Conococheague species, consisting of a wide, flat basal portion of laminae growing into numerous head-like masses large at the center and small along the edges, was described long ago by Hall as Cryptozoon proliferum. The second species, with laminae of equal undulations, is described in this volume as new.

These two types of structure are often associated together in such numbers that they form a true reef. Sometimes only one of the species will be represented in the reef, though occurring in such great numbers as to completely fill the rock. A reef composed entirely of Cryptozoon proliferum is well exposed in a cut along the Norfolk and Western Bail- road about one mile southwest of Antietam Station, Maryland (see pi. IX, fig. 1), where the highly tilted limestones expose the individual colonies of the alga to good advantage. Similar reefs of C. proliferum were observed along the northern line of outcrop from the state line south- east to Chewsville. The base of the line of low hills about a mile west of Ringgold gives numerous specimens of this species. The outcrops of the basal beds along the line five miles southeast of Hagerstown show reefs of the new species Cryptozoon undulatum most commonly.

These reefs of calcareous algae are of interest and practical value from the standpoint of structural geology because they afford an exact criterion for determining the top or bottom of a stratum. In areas of highly folded strata such as the Appalachian Valley, this determination is frequently highly important and sure methods are few. The broad upfolds of the laminations and the narrow sharp down folds register the upper and lower sides respectively of the stratum without a doubt.

Still a third type of strongly laminated Cryptozoon structure occurs near the top of the Conococheague limestone in both the eastern and western areas of outcrop in Maryland. No specimens have been obtained free from the matrix, but natural sections in the rock show that the undulations are 18 or more inches in width and that the zone of strong

86 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

undulations rises in the stratum to a height of two feet or more. This Cryptozoon sometimes consists of a single mass of strongly marked undu- lating layers one-half inch apart rising in the rock like a column. Speci- mens may be seen to advantage two miles northwest of Leitersburg along the road south of Millers Chapel, and along the Western Maryland Rail- road just west of Charlton, Maryland. This particular Cryptozoon is of special interest in having oolites one-eighth of an inch in diameter abundantly developed in the areas between the dow'nfolds of the lamina- tions (see pi. IX, fig. 2). The formation of these oolites appears to have been connected with the life activities of the plant.

Edgewise Conglomerate.

These peculiar conglomerates are such a marked feature of the Conoco- cheague limestone that they are described at this point, although they occur equally well developed in subsequent formations. The typical dark- blue, banded and frequently crinkled limestones of the Conococheague formation, are often separated by layers varying from a few inches to a foot or more in thickness, composed of a rather homogeneous or slightly granular rock filled with long, slender fragments of a distinctly different limestone tilted at various angles to the bedding plane. The actuality of the difference in composition of the two rock types making up such layers is not conspicuously evidenced on a freshly fractured surface, but weather- ing causes the slender fragments to stand out quite prominently upon exposed surfaces. The position of the fragments frequently on end or on edge in the matrix has given the common name of edgewise beds to such strata. Some of these fragments are sharp-edged and show no evidence of wave action ; others are rounded at one or both ends and have appar- ently been worn. Often the matrix of these conglomerates contain small, rounded quartz grains, evidently derived from some nearby land area.

These edgewise beds have long been considered as intraformational conglomerates and under a broad definition of that term they could still be considered so. However, the original intraformational conglomerate described by Walcott did not include this type. All of his examples are

MARYLAND GEOLOGICAL SURVEY 87

more of the nature of real conglomerates even though the fragments of which they consist are of the same age as the surrounding matrix and are not, as an ordinary conglomerate, composed of foreign rocks.

Although these curious edgewise structures have been known to geolo- gists for many years, little mention of them has been made in the literature until comparatively recently. The term " edgewise " was coined by Kason in 1901 1 and the occurrence of such structures was mentioned by Bain and Ulrich in 1905. 2 In 1906 Seely described the edgewise con- glomerate in division D of the Beekmantown limestone in the Champlain Valley as the "Wing Conglomerate," naming it after Mr. Wing who made the original observations upon it.

Seely believed that these flat pebbles could not be laid down in either swift or slow water in the position they are now found and came to the conclusion that they were organic. He described them as three species of the genus Wingia, a new genus of Beekmantown sponges.

Stose, in 1910, in the Chambersburg-Mercersburg folio of the U. S. Geological Survey, mentioned these conglomerates and ascribed their origin to the breaking up of freshly deposited thin-bedded lime sediment by shallow-water wave action into shingle or flat fragments that were shuffled about on the beach. T. C. Brown,8 in an article on the origin of certain Paleozoic sediments, reverted to the organic origin of the pebbles, but concluded they resulted from the activities of calcareous algae. He admitted that no specimens preserving any organic structure sufficiently well to prove their origin had been found. Another interesting origin for these conglomerates is that discussed by Grabau in his Principles of Stratigraphy where he explains that they are due to deformation through gliding which has resulted in the complete brecciation of the layers. He distinguishes the intraformational conglomerates in which the fragments lie in all positions, and the edgewise conglomerate where the gliding process has caused the thin cakes to assume a vertical position in the rock

1 Amer. Jour. Sci., 4th ser., vol. 12, p. 360.

2 Copper deposits of Missouri, Bull. 267, U. S. Geological Survey, p. 23.

3 Journal of Geology, vol. xxiii, No. 3, 1913.

88 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND

mass. No such distinction as this can be drawn in nature because there are all gradations of arrangement.

The observations of Ulrich, Stose, Butts and other geologists who have had numerous opportunities to study the edgewise beds, all tend to the conclusion that these conglomerates are not organic; but are composed of fragments formed on tidal flats by mud cracks. The Appalachian early Paleozoic formations are practically all shallow-water deposits in which the area was often subject to uplift above the sea level. Mud flats which by uplift are exposed to evaporation soon develop the usual shrinkage figures known as sun cracks and the edges of these to-day curl up and are broken off and tossed about by the wind. This same condition has occurred time and again in the past, and indeed limestones still preserving well-defined sun cracks with the edges curled up and ready to be formed into edgewise conglomerates have been observed.

FOSSILS OF CAMBRIAN AGE

In spite of the considerable thickness of Cambrian rocks developed in the Appalachian region of Maryland, and the careful search that has been made, fossils of this age are exceedingly rare. Usually no trace of organisms can be detected in the rocks, and the few specimens noted have always been fragmentary and poorly preserved. These few remains occur in the Harpers schist, Antietam sandstone, and Tomstown limestone of Lower Cambrian age, in the two Middle Cambrian formations, the Waynesboro formation and Elbrook limestone and in the Upper Cambrian (Ozarkian), Conococheague limestone. The basal Cambrian Loudon formation and the succeeding Weverton quartzite are lithologically of such a nature that fossils would not be expected in them, but the over- lying formations are more promising in this respect and may possibly yield to some fortunate collector more respresentative faunas than known at present. Fairly well-developed Lower and Middle Cambrian faunas are known in the Appalachians both north and south of Maryland, but it appears that the strata bearing them are usually not represented in the Maryland section. For example, the Lower Cambrian strata at York,

MARYLAND GEOLOGICAL SURVEY 89

Pennsylvania, containing well-preserved trilobites, do not appear to be present in Maryland.

The few species thus far discovered in the Conococheague limestone of southern Pennsylvania and Maryland give no idea of the characteristics of the Upper Cambrian (Ozarkian) faunas. It is true that the two species of Cryptozoon are. characteristic Ozarkian fossils over a wide area, but very similar species are found in the succeeding Ordovician strata. The single species of trilobite is very limited in its distribution and the brachiopod is too little restricted to be of any stratigraphic value.

The few Cambrian species identified in Maryland strata are described in the following pages. These species are listed below under their appropriate formations :

Lower Cambrian (Waucoban) Fossils of Maryland

Harpers shale. Scolithus linearis Haldemann.

Antietam sandstone. Scolithus linearis Haldemann, Obolella minor (Walcott),

Hyolithes communis Billings, and Olenellus thompsoni (Hall). Tomstown limestone. Olenellus thompsoni (Hall) and Salterella sp.

Middle Cambrian (Acadian) Fossils

Waynesboro formation. Lingulella sp. Elbrook formation. Dolichometopus sp.

Upper Cambrian (Ozarkian) Fossils Conococheague Limestone

Cryptozoon proliferum Hall (common at base) Cryptozoon undulatum n. sp. (common at base) SauJcia stosei Walcott (rare in upper part) Eoorthis desmopleura (Meek) (rare in upper part)

THE BEEKMANTOWN LIMESTONE

The middle part of the Appalachian Valley in Maryland, with the exception of the Martinsburg shale belt which is three miles in width, and small areas or other formations, is directly underlain by a thick mass of rather pure limestone. Nearly all of this rock is fine grained and most of it is minutely laminated. Interbedded with these are pure minutely

90 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND

laminated limestones with some layers containing occasional, more or less massive., ledges in which the lamination is obscure. Some of these con- tain numerous poorly preserved fossils. Study of these fossils shows that a large part of the local fauna consists of species previously found in the Beekmantown limestone of the Champlain Valley in New York, Vermont, and southeastern Ontario. In 1910 * the northern extension of these strata was distinguished and separately mapped under the same name by which the formation is known in New York.

The Frederick Valley in Maryland, east of the Blue Ridge, also con- tains a considerable development of rather pure massive limestone hold- ing Beekmantown fossils. This development of the Beekmantown is discussed in a separate chapter, so that the following description of the stratigraphy applies only to the Appalachian Valley. As a whole, the Beekmantown limestone of Maryland is quite distinct lithologically from the other divisions of the Shenandoah group, although the occurrence of similar beds in most of the formations often causes difficulty in the recognition of isolated outcrops. Its strata are most likely to be confused with the underlying Conococheague limestone, because edgewise con- glomerates are not uncommon in the Beekmantown, in fact in the upper half of the lowest division they are as well developed as in the Conoco- cheague limestone. The characteristic sandy laminated banded, dark blue rock of the latter, excepting one bed, is not developed in the Beek- mantown. The main mass of the Beekmantown formation is of finely laminated, lighter colored and purer rock than occurs in the Conoco- cheague. The successive beds also are more uniform in texture, color and composition. On this account, it is difficult to distinguish the different portions above the basal division, which contains the exception mentioned above in which siliceous banded limestones occur.

Fortunately there are four fossiliferous zones in the formation with characteristic species in each, which appear frequently enough in the outcrops to obviate some of the difficulties of determination. Several distinct zones in this formation may also be recognized by residual

1 Chambersburg-Mercersburg folio, U. S. Geological Survey.

92 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND

products left in the soil by the weathering of the limestone. The top, middle and lower portions are especially well characterized by siliceous products, such as chert, flint and sandy shale fragments, which are dis- cussed in detail in succeeding paragraphs. •

LITHOLOGIC • CHARACTER. — Although the Beekmantown limestone differs considerably in its lithological development in the eastern and western parts of the valley, the formation as a whole is composed of much purer limestones than the underlying Conococheague. On the other hand its purest beds are inferior in calcium carbonate content to the high average of the overlying Stones Kiver limestone. The purer limestones of the Beekmantown are interbedded with greater thickness of relatively impure finely laminated beds which occur, or at least outcrops, so fre- quently that the presence of these laminated limestones is a good criterion for the formation. This characteristic minute lamination of the average rock of the formation is due to impurities in the rock and most apparent on weathered surfaces. Pink and white fine grained marbles in ledges of considerable thickness also are of common occurrence in the Beekman- town, especially in the lower half of the formation. Marbles occur in the underlying Conococheague limestone, but as they are always associated with the characteristic siliceous banded limestone of that formation they are readily distinguished from the marble beds of the Beekmantown. But it should not be forgotten that siliceous banded limestones quite similar to those of the underlying Conococheague beds occur also in the lower fifth of the Beekmantown. These are so constantly developed in tho eastern half of the valley that the part containing them has been mapped as a distinct basal division under the name of the Stonehenge limestone member. This basal member can be recognized locally also in the western part of the valley, but here its lithologic characters are hardly distinct enough to warrant its separation in the mapping.

As practically all of the Beekmantown areas of Maryland are covered by gently rolling cultivated farm lands it is almost impossible to make out the complete section of the formation in any particular place. How- ever, by assembling incomplete sections in various parts of the valley the

MARYLAND GEOLOGICAL SURVEY 93

following generalized section for Maryland and southern Pennsylvania lias been described by Ulrich in his Revision of the Paleozoic Systems : '

Generalized Section of Beekmantown Limestone in Southern Pennsylvania

and Maryland

Feet Base of Stones River limestone with quartz pebble conglomerate and

cauliflower chert

Hard dense white chert and granular quartzose chert forming by

secondary silicification, cauliflower chert 40

Fine grained gray, finely laminated, interbedded pure and magneslan unfossiliferous limestone with sandy chert and limestone and

dolomite conglomerates at the top 400

Turritoma zone. Thin bedded argillaceous and massive purer limestone containing the Turritoma fauna. Many of the beds weather so as to appear riddled with worm borings 200

Alternating beds of pure dove, pure gray and magnesian gray unfos- siliferous limestone often laminated, with occasional beds of fine limestone conglomerate 300

Massive pure dove gray and magnesian limestone terminated above by sandy fossiliferous chert containing Syntrophia later alls,

Maclurites sordida and species of Liospira 75

Ceratopea zone. Blue and dove fossiliferous limestone cherty in the upper half, containing Ceratopea and associated fossils. At the base is

a blue limestone filled with rounded quartz grains 250

Cryptozoon steeli zone. Fine grained nearly pure limestone with some

magnesian beds and several layers of porous chert 275

Dove, pink and bluish fine grained pure limestone and marble 300

Oolitic, cherty blue and gray limestone holding the Cryptozoon steeli

fauna and weathering into platy yellow chert 60

Stonehenge limestone member. Massive dark blue to gray limestone with contorted argillaceous and siliceous laminations weathering to sandy shale, interbedded with edgewise beds and oolites 250

Massive blue to gray pure limestone weathering white, with cepha-

lopods and gastropods occurring in reef structures 250

Top of Conococheague limestone with sandy laminae and beds of edgewise

conglomerate

2400

From the stratigraphic standpoint the important divisions of the above section are the Stonehenge member and the three zones marked respec- tively the Cryptozoon steeli, Ceratopea, and Turritoma zones. The faunal and other characteristics of these zones are discussed in succeeding paragraphs.

1 Bull. Geol. Soc. America, vol. xxii. No. 3, 1911, pp. 652-655.

94 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND

While the general section given above holds fairly well for all parts of the Valley, the detailed stratigraphy of the formation in the eastern and western parts is, as mentioned above, somewhat different. The best exposure of the Beekmantown limestone east of the Martinsburg shale belt is adjoining the Chambersburg-Gettysburg Pike one mile east of Chambersburg, Pennsylvania. This section, measured by Ulrich and Stose, is given below with slight emendations to show the position of the fossil zones.

Section of Beekmantown Limestone One Mile East of Chambersburg,

Pennsylvania

Feet

Base of Stones River, containing fine limestone conglomerate and laminar

and oolitic chert

Interbedded fine-grained pure and magnesian limestones, finely laminated in part and containing small quartz geodes; porous sandy chert near top; dark-blue layers near base containing numerous gastropods (Turritoma fauna) and ostracods and mottled by magnesian material that weathers out, leaving pits and holes 600

Alternating pure dove-colored and gray limestone and magnesian lime- stone, with layer of sandy chert 375

Bluish to dove-colored fine-grained fossiliferous limestone, at the base

containing rounded quartz grains. Ceratopea fauna at top 100

Pink fine-grained marble, containing layers of milky quartz chert; gastropods' of the genera Ophileta, Maclurites and Eccyliopterus rather abundant 275

Pure dove-colored and blue fine-grained limestone, with some pink lime- stones; contains fragments of trilobites 285

Fine-grained dove-colored to dark gray limestone with fine conglomerate and oolite beds; abundant chert in upper portion, in part oolitic and conglomeratic. Cryptozoon steeli in middle part 145

Stonehenge limestone member: .'

Fine-grained light to dark gray limestone containing wavy laminae of sandy matter that stand in relief or fall to sandy shale on weathering and thick beds of " edgewise " conglomerate; gastro- pods in upper and fine fragments of trilobites in lower portion. . 225 Dark to very light gray massive limestone, containing Dalmanella,

Ophileta and trilobite fragments 260

Top of Conococheague, containing wavy and sandy laminae and beds of

coarse limestone conglomerate

2265

"West of the shale belt, the details of the Beekmantown section are somewhat different, although the several fossil zones can be readily

MARYLAND GEOLOGICAL SURVEY 95

recognized. No continuous well-exposed section of these strata was noted in Maryland, and the section repeated below is one, published by Ulrich and Stose,1 of the northern continuation of the formation in southern Pennsylvania. This section is broken and probably incomplete 480 feet beneath the base of the overlying Stones Kiver limestone. If the Turri- toma zone which was not observed is present in this basin, it may have been faulted out or is concealed by covering soil and debris. However, it has been recognized in the southern continuation of the belt in Maryland.

Section of Beekmantown Limestone near Mouth of Licking Creek, Franklin County, Pennsylvania

Feet

Interbedded pure and magnesian limestone of Stones River type

Light-gray, finely laminated magnesian limestone and white dolomite

with cherts of rosette type at the top 340

Dark and light coarse dolomite 140

Rocks folded and largely covered; white dolomite, dark-blue oolitic lime- stone, and dark coarse dolomite with yellow blocky sandstone frag- ments and rosette cherts; exact continuity indeterminable, but the previous beds are apparently repeated by folding

Interbedded pure and magnesian limestone, with beds of coarse dark dolomite, and in the lower part beds of " edgewise " conglomerate; at base contains Ceratopea gastropods, cephalopods, and trilobites 350

In large part finely banded magnesian limestone with few pure lime- stones; contains fine conglomerate beds and gastropods 170

Largely dolomite, some coarse and dark; large scoriaceous black chert

and coarse sandstone at the base 130

Chiefly dolomite, coarse and dark in upper part, with some pure fos- siliferous limestone; bed of granular limestone with numerous Ophileta and pinkish fine-grained limestone near middle; cross- bedded banded limestone at base, locally unconformable on under- lying beds 290

Fine-grained limestone seamed with calcite and dolomite beds with flinty

chert containing Cryptozoon steeli at the base 65

Partly covered; lower part pure dark limestone with a few beds of finely laminated magnesian limestone and fine white oolite near base; small rough chert with casts of crystals at the base 130

Light-blue limestone with fine contorted sandy laminae that weather in relief; contains fine dark conglomerate with red limestone pebbles and fragments of trilobites 165

Purer fine even-grained limestone with few sandy partings 530

Sandy laminated limestone, much contorted (Conococheague)

2310

1 Chambersburg-Mercersburg folio U. S. Geological Survey.

7

96 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

Comparison of these sections brings out several salient differences in the lithology of the two areas. East of the shale belt, the Stonehenge member with its characteristic siliceous banded limestone, is distinct enough to be mapped as a separate unit, but west of that belt the siliceous banding of the lower Beekmantown is not so well developed. However, the same faunas are present in these strata in both areas so that there is no doubt as to the presence of beds corresponding to the Stonehenge member in both. The higher beds in each area also contain similar faunas, but the lithology is somewhat different, limestone predominating in the east and dolomite in the west. Chert in large quantities weathers from certain portions of the dolomite in the western area, but it is not so conspicuously developed in the east.

The two sections illustrate the lithologic changes occurring in the formation going from the east, where over three-fourths of the formation consists of pure limestone, across the strike to the western side of the Valley where more than half of the strata is more or less highly magnesian. In Appalachian areas still further west, as in central Pennsylvania, the change to magnesian limestone becomes yet more pronounced.

FAUNAL ZONES. — Although the lithologic features of the various por- tions of the Beekmantown limestone vary considerably, the basal member is the only division which can be definitely recognized from the character of its strata. Above this lower division — the Stonehenge member — three distinct fauna! zones aid in the recognition of their respective horizons. These are in ascending order above the Stonehenge member, the Crypto- zoon steeli zone, the Ceratopea zone and the Turritoma zone. The value of these zones is not local for they have a wide distribution.

Stonehenge Member. — The village of Stonehenge, just east of Cham- bersburg, Pennsylvania, is located on the lower beds of the Beekmantown, which are sufficiently distinct lithologically and faunally from the remain- ing strata of the formation to warrant their separation as a distinct member. This Stonehenge member is composed of massive finely con- glomeratic pure limestone in the lower half and siliceous banded limestone alternating with layers of large edgewise conglomerate in the upper half.

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE XIII

FlG. I. — EXPOSURE OF STEEPLY INCLINED STONEHENGE LIMESTONE (UPPER DIVISION) AT CHARLTON, MARYLAND, SHOWING THE DISINTEGRATION INTO SILICEOUS SHALE, UPON PRO- LONGED WEATHERING.

FlG. 2. — TYPICAL EXPOSURE OF EDGEWISE CONGLOMERATE FROM THE UPPER PART OF THE STONEHENGE LIMESTONE, BALTIMORE AND OHIO RAILROAD, ONE MILE NORTH OF BALLS, MARY- LAND.

MARYLAND GEOLOGICAL SURVEY 97

The lower Stonehenge limestone is made up in large part of very massive blue to dove-colored limestone weathering bluish-white or white. The outcrops are always of a distinctly lighter color than the associated formations. This feature is one of several that serve unmis- takenly in identifying this basal zone of the formation. On close inspec- tion a large part of these massive limestone ledges appears to the un- assisted eye as granular in texture, but under a lens the granules prove to be very small brecciated pieces of limestone usually less than a sixteenth of an inch in diameter. These small fragments are of a more distinctly white color than the surrounding matrix and the combination of a light blue rock crowded with lighter colored minute angular fragments is very distinctive. The lower division is further distinguished by absence of chert. In all of the numerous outcrops that have been studied no chert of any kind has been observed either in the weathered limestone or in the soil derived from it. At intervals varying from an inch to two inches the limestone develops very thin layers of carbonaceous or argillaceous material which gives it a banded aspect. These layers or laminae are usually about one-eighth of an inch in thickness, flat and parallel with the bedding planes. They are quite unlike the sandy intertwining laminae so characteristic of the upper division of the Stonehenge member.

Along the National Highway just south of Funkstown there are splendid outcrops of typical lower Stonehenge limestone where fossils may be found and its lithologic character can be studied to advantage. Hagerstown and vicinity also affords numerous, excellent and instructive exposures of those beds.

Excepting the shells of a few brachiopods the fossils in this zone cannot be cleanly extracted from the rock because they are so firmly cemented to the fine-grained matrix that in breaking the limestone with a hammer the fracture passes through the fossils and not along their surfaces. It is only upon the weathered surfaces of the ledges that the fossils can be discerned, and at that merely as cross-sections. The exposures near Funkstown have shown clearly that the fossils of the lower Stonehenge fauna, especially the cephalopods and gastropods which constitute much

98 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OP MARYLAND

the greater part, occur mainly in reef-like masses. These reefs are of slightly different material than the enclosing rock, lenticular in form, and seldom exceed two feet in maximum thickness. Straight and coiled cephalopods are the most abundant fossils seen in cross-sections of these reefs, but Maclurites and Ophil eta-like gastropods are not uncommon.

Most of the beds of the upper Stonehenge resemble the Conococheague limestone so closely in their development of sandy laminated strata with numerous beds of edgewise conglomerate that in areas of faulted or intricately folded strata the distinction between the two formations is made with difficulty. The absence of chert in the weathered Stonehenge limestone contrasting with its frequent occurrence in the Conococheague is perhaps the best of the physical means of separation. It will be observed also that in the upper Stonehenge the sandy laminae are more undulating and interwoven than in the laminated beds of the Conoco- cheague in which commonly they form relatively parallel bands. The •presence of shells of cephalopods and gastropods in the Stonehenge also serves to distinguish this member from the Conococheague which has never yielded any molluscan fossils. In areas where the sequence is normal the boundary between the two formations is readily determinate by the criteria given. Desirable and conclusive corroboration may be secured by establishing the lower Beekmantown sequence of ( 1 ) the lower Stonehenge composed of pure dove-colored to gray strata containing beds of a minute limestone conglomerate; (2) dark impure limestone with undulating siliceous laminae followed by (3) relatively pure limestone consisting largely of pinkish marbles.

All the hills within the city of Hagerstown and its vicinity are formed of the upper Stonehenge limestone, .and as the quarries for building stone in the early days were located on these hills, it follows that many of the older buildings in Hagerstown are of this limestone. The stone is not only easily quarried and dressed, but as it whitens in weathering and the edgewise conglomerate and wavy laminae become distinctly visible, it has also a handsome and unique appearance. Several of the churches are constructed of Stonehenge limestone and its value and beauty as building rock may be seen particularly in St. John's Episcopal Church on West Antietam Street, and the Presbyterian Church at the corner of Wash-

MARYLAND GEOLOGICAL SURVEY : 99

ington and Prospect streets. The conglomeratic nature of the rock is especially well brought out in the many stone embankments about Hagerstown in which long exposure to the weather has emphasized this and the laminated character. At the present time brick and concrete construction have largely displaced this limestone as building material.

Although the upper division of the upper Stonehenge is well exposed at many localities in Maryland, perhaps the best places to study it in detail are in the various railroad cuts around Hagerstown. The cut on the Western Maryland Eailway one-half mile west of Bissel exposes the characteristic edgewise conglomerate and the heavy, wavy laminae espe- cially well. At this place, as well as at other localities around Hagers- town, a few granular layers are found crowded with brachiopods and poorly preserved gastropods.

Seventeen species of fossils have been noted in the Stonehenge lime- stone of Maryland and Pennsylvania. Following Ulrich 1 these have been correlated with the Tribes Hill limestone fauna of New York. The same fauna is found also in the upper part of the Kittatinny limestone in New Jersey and in the basal or Stonehenge limestone division of the Canadian in central Pennsylvania. The brachipod Dalmanetta wemplei Cleland is found in abundance in certain granular layers, but other fossils are not so common. The cephalopods are almost confined to reef -like structures in the purer limestones of the lower half. The gastropod Ophileta com- planata Vanuxem is found in both the lower and upper parts of the member and it may be considered the characteristic fossil.

Bepresentatives of one species of fucoid and 16 species of invertebrates, including one brachiopod, six gastropods, five cephalopods, three trilo- bites, and one branchiopod crustacean, have been found in the Stonehenge member in Maryland sufficiently well preserved for specific identification. Fragments of a few more species too imperfect for accurate determination have also been noted. The gastropod Ophileta complanata is highly characteristic of this part of the Beekmantown and the fauna may be known as the Ophileta complanata fauna. The Stonehenge limestone

1 Ulrich, Revision Paleozoic Systems. Bull. Geol. Soc. America, vol. xxii, 1911, No. 3, pi. xxvii; Ulrich and Gushing, Age and Relations of the Little Falls dolomite— N. Y. State Museum, Bulletin 140, 1910, p. 137.

100 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

does not leave any residual chert upon weathering and its contained fossils unfortunately do not become silicified. As a result, their preserva- tion is not of the best and natural sections in the rock or poor casts are the rule. The granular beds associated with the edgewise conglomerate of the upper part of the Stonehenge limestone is the most favorable place for collecting the brachiopod and gastropod shells, some of these beds being fairly crowded with specimens of Dalmanella wemplei. The cephalopods and trilobites have in the main been found in reef-like structures in the lower Stonehenge and their occurrence is therefore quite sporadic. At one point a stratum will exhibit numerous cross-sections of fossils, but a foot or two away where the reef material composed of a very fine edgewise conglomerate has disappeared, no trace of a fossil can be found.

The following table gives a list of the Stonehenge fauna and shows the distribution of the species in the Kittatinny limestone (upper part called the Coplay limestone) of New Jersey and the Tribes Hill limestone of New York, formations with which on strati graphic and paleontologic grounds, the Stonehenge is correlated.

LIST OF STONEHENGE LIMESTONE FOSSILS SHOWING DISTRIBUTION

	Kittatinny lirntstone upper beds) of New Jersey	Tribes Hill limestone of New York	Other hori- ZO I'S Of Beekmaii- to\vn	Stonehenge limestone of Pennsyl- vania and Maryland
Pdlcrophycus tubulare Hall		*		*
Ddlinunello wemplei C leland	*	*		*
Ophileta complanata Vanuxem		*		*
Ophileta levata Vanuxem .		*		*
Eccyliomphalus multiseptarius Cleland. . . Plcurotomaria ?? floridensis Cleland Raphistoma f obtunum Cleland		* * *		* # *
Raphistoma f columbianum Weller	*			*
Orthoccras primigenium Hall		*	*	*
Ooceras kirbyi Wh itfield		*	*	*
CyrtoceTas qracile Cloland	*	#		#
Cyrtoceras beekmanense Vv bitfield Cyclostomiceras cassinensef (Wh itfield).. Asaphell.us gyracanthus Raymond	*	*	* *	* * *
Hemigyraspis collieana Raymond				*
SymphyfsuTiift convexus (Cleland)	*	*		*
Ribeiria nuciilitiformis Cleland		*		*

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE XIV

no. 1. — VIEW OF A WEATHERED OUTCROP OF THE UPPER STONEHENGE LIMESTONE, EASTERN EDGE OF HAGERSTOWN, MARYLAND.

2. VIEW TAKEN FROM HILL OF UPPER STONEHENGE LIMESTONE, EASTERN EDGE OF

HAGERSTOWN, MARYLAND, LOOKING EAST, SHOWING EFFECT OF WEATHERING OF THE VARIOUS FORMATIONS UPON TOPOGRAPHY. THE VALLEY IN THE FOREGROUND IS IN THE LOWER STONEHENGE PURE LIMESTONE WHILE THE RIDGE IS FORMED OF THE SILICEOUS, MORE RESISTANT UPPER STONEHENGE. SOUTH MOUNTAIN IS SEEN IN THE DISTANCE.

MARYLAND GEOLOGICAL SURVEY 101

In Maryland and southern Pennsylvania, the Beekmantown strata fol- lowing the Stonehenge member are so uniform in lithologic character that their separation into distinct formations is impracticable. In the Nittanny and other valleys in central Pennsylvania the corresponding strata not only attain a much greater thickness, but also are so developed that four formations are readily distinguishable. These are, in ascending order, (1) the Stonehenge limestone at the base with a thickness of 662 feet; (2) the Nittanny dolomite, 1267 feet thick, cherty and holding the Cryptozoon steeli fauna in its lower part; (3) the Axeman limestone 158 feet, and (4) the Bellefonte dolomite 2145 feet thick. The entire series, with both overlying and underlying formations, is to be seen in excellent and practically continuous exposures at Bellefonte, Pennsyl- vania. As this section gives the maximum known development of the Canadian system in the Appalachians, the four formations into which it has been divided as above by Ulrich have been adopted in the general time scale.

Cryptozoon steeli Zone. — Following the Stonehenge member, which has just been described, are 600 or more feet of cherty oolitic limestones, dove- colored, fine-grained pure limestone and usually dense textured pink marble. The basal 60 feet consisting mainly of oolitic cherty limestone contains the characteristic fossil of this division — a globular mass, com- monly four to eight inches in diameter composed of concentric layers and supposed to represent the secretion of calcareous algae to which the name Cryptozoon steeli has been applied. Though doubtless calcareous originally, these rounded masses are now almost without exception more or less completely replaced by silica in the' form of chert. This fossil occupies a similar position in the Beekmantown throughout the Appa- lachian Valley and it is so abundant and characteristic that this division is termed the Cryptozoon steeli zone. Subaerial decomposition of these particular strata leaves a light reddish residual clay and soil containing an abundance of ordinary yellow "platy chert besides the numerous rounded silicified masses of Cryptozoon. These cherty residual masses unfailingly identify the outcrop of this zone. It is particularly well exposed in the

102 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

railroad cut about three-fourths of a mile east of Charlton, Md. Here deep weathering and decomposition of the steeply dipping limestone strata has removed their calcareous matter and left only residual clays with the chert clearly marking its position. The abundance of chert and silicified Cryptozoon heads formed in the weathering of this zone is well attested by the frequent piles of chert collected along the roadways.

Immediately following this cherty zone with Cryptozoon are 300 feet of dove and pink fine-grained pure limestone, of which a considerable portion can be called marble. These marble beds are well shown in several railroad cuts around Hagerstown. Fossils are rare in these strata, but an occasional layer shows traces of species found also in the underlying beds holding Cryptozoon steeli. This zone ends with 275 feet of fine-grained, nearly pure limestone with occasional beds of magnesian limestone and several layers of porous chert.

The platy chert, weathering out of the limestone of the Cryptozoon steeli zone is common at all outcrops of the zone, but is so abundant in the western half of the valley that it occasions a distinct row of hills marking the line of outcrop. This topographic feature and the numerous masses of Cryptozoon associated with the chert cause this portion of the Beekman- town to be easily recognized. The following species have been found either associated with Cryptozoon steeli or in strata underlying it, but still included in this division :

Fossils of Cryptozoon steeli Zone

Cryptozoon steeli Seely Rhabdaria fragilis (Billings) Tetradium simplex new species Syntrophia lateralis (Whitfield) Maclurites affinis (Billings) Eccyliopterus triangulus (Whitfield) Ophileta compacta Salter Hystricurus conicus (Billings)

At the very base of this zone two interesting fossils have been found associated with the usual gastropods. These are the sponge-like organism Rhabdaria fragilis Billings and Tetradium simplex, a new species of coral of particular interest in being the oldest known undoubted coral.

MARYLAND GEOLOGICAL SURVEY 103

The Maryland outcrops of the Cryptozoon steeli zone are so numerous and easily located both on the map and in the field that only a few locali- ties need be mentioned. In the western half of the valley, outcrops along the Western Maryland Railway, especially three-quarters of a mile east of Charlton, show these rocks and their contained fossils. East of the Martinsburg shale belt, exposures in the vicinity of Williamsport and also north and west of Hagerstown have afforded fossils. In the western part of the valley the line of hills in the Beekmantown area next to the Beekmantown-Conococheague boundary represents this zone, but in the eastern part the exposures parallel a line of hills caused by the more resistant Stonehenge beds.

Ceratopea Zone. — Succeeding the dove and pink pure limestones and marbles of the Cryptozoon steeli zone are 250 feet of blue and dove lime- stone cherty in the upper half, containing horn-like fossils known by the generic name Ceratopea. The exact nature of these fossils is unknown, but they are believed to be the opercula of large gastropods like Maclu- rites. From a stratigraphic standpoint they are of considerable interest because this particular species and the fauna associated with it has a wide geographic distribution, but restricted geologic range throughout the Appalachian and Mississippi valleys. Free silicified specimens of this organism occur in the soil where this zone outcrops, or they may be found attached to the limestone. Associated with the Ceratopea are a few species of gastropods and fragments of trilobites, but the Ceratopea itself is the most characteristic fossil of the division. In Maryland numerous outcrops of this zone can be found in the vicinity of Halfway, particularly in cuts along the Cumberland Valley Railroad. Localities near Hagers- town have also afforded this fossil, although in no place has it been found in the abundance that prevails in Virginia and the states to the south.

The fauna of the Ceratopea zone so far identified consists of nine species. Fragments of a few other species have been noted, but they are too imperfect for description and can only be identified with certainty when a monographic study of the entire Beekmantown formation has been made.

104 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

Fossils of the Ceratopea Zone

Dalmanella electro, (Billings) Pleurotomaria ff canadensis Billings Hormotoma artemesia (Billings) Maclurites sordidus (Hall) Ceratopea keithi Ulrich Raphistomina laurentina (Billings) Goniurus caudatus (Billings) Pliomerops salteri (Billings) Isochilina gregaria (Whitfield)

Turritoma Zone. — The next division of the Beekmantown consists of about 575 feet of pure dove and gray laminated magnesian limestone, which contains in its upper part high-spired gastropods with a species of Turritoma apparently confined to these beds. The lower 375 feet of the Turritoma zone is composed of alternating highly magnesian, finely laminated gray limestones and pure gray and pure clove limestone with occasional beds or streaks of fine limestone conglomerate. The basal 75 feet' of this portion occasionally exhibits a few fossils of which Syntrophia lateralis and species of Maclurites and Liospira are most often found.

The association of species called the Turritoma fauna is found only in the upper 200 feet of this division where the fossils usually occur in beds that weather so as to appear riddled with worm borings! Here the fossils are not silicified, but they occur as dolomitic casts, often, however, in good preservation. They are extremely fragile and much care is required to preserve them. Gastropods, particularly the species Turritoma acrea (Billings), are most conspicuous. A number of species of fossils, too imperfectly preserved for recognition, occur in this zone in Maryland; eight species have been identified specifically. The strata with Turritoma are the uppermost fossiliferous rocks of the Beekmantown, but they are followed by 400 feet of finely laminated, gray, interbedded pure and magnesian limestone of the type considered characteristic of the forma- tion as a whole. At the top of these finely laminated beds are sandy cherts and hard, dense white chert marking the top of the Beekmantown. Asso- ciated with these cherts and continuing upward for about 40 feet are great numbers of the secondarily silicified cherts which have assumed

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE XV

FlG. I. — EXPOSURE OF LOWER BEEKMANTOWN LIMESTONE JUST ABOVE THE STONEHENGE MEMBER IN BRICKYARD, EASTERN EDGE OF HAGERSTOWN, MARYLAND. CLAY FOR BRICK MANUFACTURE RESULTS FROM THE WEATHERING OF THE PURER BEDS.

FlG. 2. — BEEKMANTOWN LIMESTONE AT LEGORE QUARRY, LEGORE, MARYLAND. THE WEATHERED OUTCROPS OF THESE STRATA HAVE YIELDED NUMEROUS CEPHALOPODS.

MARYLAND GEOLOGICAL SUKVEY 105

the form of a cauliflower. These mark the boundary between the Beek- mantown and Stones River limestones. As explained on another page, the secondary silicification necessary to form the cauliflower variety is supposed to have occurred in the time interval between the two formations when the Beekmantown rocks formed a land area.

Sometimes the upper Beekmantown strata holding the Turritoma fauna do not weather as described above, but show the usual occurrence of smooth, rounded outcrops in which the fossils, although numerous, appear only as natural sections in the rock. Such exposures along the National Highway in the vicinity of Huyett, Maryland, have yielded the following species :

Fossils of the Turritoma Zone in Maryland

Dalmanella electro, (Billings) Pleurotomaria ?? gregaria, Billings Hormotoma gracilens (Whitfield) Turritoma acrea (Billings) Maclurites oceanus (Billings) Eccyliopterus disjunctus .(Billings) Cyrtocerina mercurius Billings Trocholites internistriatus (Whitfield) Isochilina seelyi (Whitfield)

Traces of this fauna, although always in poor preservation, have been noted at numerous places in Maryland, in fact Beekmantown strata exposed near the boundary line of the Stones Eiver areas usually reveal one or more layers showing natural sections of these fossils.

TOPOGRAPHY AXD RESIDUAL PRODUCTS. — The Beekmantown as a whole produces gently rolling country, but the lower Stonehenge member and a zone about 800 feet above the base of the formation give rise to very characteristic topographic features, which are of extreme importance ill the mapping of areas in which rock outcrops are infrequent.

These topographic features are the result of the various siliceous products left in the soil by weathering of the limestone. They are so distinctive that they become as important factors in the identification of the strata as the .characters of the rock itself or of its contained fossils. In the absence of fossil remains or indeed of satisfactory rock

106 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

outcrops it is often possible to determine the underground stratigraphy by the character of these surface residual products alone. In fact such criteria were alone available over considerable stretches of the rolling agricultural country with few rock exposures, that in this region at least, is characteristic of Beekmantown limestone areas. On this account, although they have been mentioned incidentally and repeatedly in fore- going pages, it seems desirable to give here a connected discussion of the three most important residual products, namely, the siliceous shale frag- ments near the base of the formation, Cryptozoon and platy yellow chert near the middle, and the cauliflower chert at the top.

The relatively pure limestone of the lower half of the Stonehenge member weathers rapidly and as its surface is not held up by some resistant residual a slight depression in the land surface results. On the other hand, the upper half of the Stonehenge member, with its sandy laminated strata weathering into a protective covering of thin siliceous shale fragments, forms hills corresponding in width to the outcrops and trending in the direction of the strike of its beds. As the Beekmantown everywhere in the Appalachian Valley of Maryland is highly folded, these hills assume the usual northeast-southwest direction of the folds and their development is so marked a feature that by plotting these elongated narrow hills, the upper Stonehenge member can be mapped in areas of few outcrops of the rock itself. When the succession is normal the lower Stonehenge limestone therefore occurs in a slight valley between the low hills of the upper Stonehenge on one side and the higher land on the other side formed by the chert weathered out of the upper part of the Conoco- cheague limestone. This topographic feature, however, is well developed only to the east of the Martinsburg shale belt. West of this belt the siliceous content of the laminated division of the Stonehenge is so much less that it has little effect on the topography. This topographic feature of the Stonehenge in connection with the line of hills next described makes it possible to map the complicated folds involving the Beekman town limestone without much doubt and has greatly aided in deciphering the geologic structure in areas of few outcrops. The Beekmantown rocks next or immediately succeeding following the Stonehenge divisions are

MARYLAND GEOLOGICAL SURVEY 107

of a more soluble nature and therefore weather into lowland areas again. Therefore the broad area of folded Beekmantown limestones in which Hagerstown is located presents a succession of elongated highland areas alternating with usually broader lowland areas. This alternation in the topography is well shown in Hagerstown itself, where the hills passing through the town are composed of upper Stonehenge limestone and the low areas between them are underlaid by lower Stonehenge or by the over- lying Beekmantown limestone.

The line of low hills formed by the upper member of the Stonehenge limestone is a characteristic feature of the Beekmantown topography only, as noted before, in the eastern half of the Appalachian Valley of Maryland, because west of the Martinsburg shale belt the siliceous nature of this -member is not so well developed and consequently weathers much like the remaining portions of the Beekmantown. The marked topo- graphic feature of the western belt of outcrops is a line of hills composed of the chert derived from the Cryptozoon steeli zone of the formation which is unusually well developed in this part of the Valley. Here speci- mens of the Cryptozoon are very abundant, and as they silicify upon weathering, their remains leave considerable masses of chert in the soil However, the greater part of this residual material consists of yellow, platy, flinty chert formed by replacement of certain layers of the lime- stone. The Beekmantown limestone weathers so readily that the deter- mination of the geologic structure of the formation in many cases would be almost impossible were it not for this extensive development of Crypto- zoon and its accompanying chert. This chert zone is plotted on the map of the western part of the Valley where it gives a clue to the lower boundary of the formation and also aids in determining the structure. For example, the small synclinal area on the west flank of the larger synclinal area three miles northeast of Clear Spring is an interesting case of this zone's value in determining structural relations.

The cauliflower chert developed at the top of the Beekmantown does not occur abundantly enough or through a sufficient thickness of strata to form a topographic feature, but the unusual shape of these flinty objects is so characteristic that their presence in the soil is the surest

108 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

criterion in determining the dividing line between the Beekmantown and the overlying Stones River limestone. These cherts are believed by some students to represent in reality the physical evidence of the uncon- formity between these two great limestone formations. Unlike many other cherts they are not the result of present-day surface weathering, but appear to have been formed in the land interval between the two forma- tions. These cherts occur as a regular bedded deposit and their origin seems to be as follows :

With the uplift at the end of Beekmantown time, weathering of the exposed limestones took place, resulting, as it does to-day, under favorable conditions, in a soil with more or less numerous chert fragments. Con- tinual exposure to waters bearing silica in solution caused a secondary silicification of these cherts by the formation of rosettes of silica over their surface. The rosette areas continued to grow larger and larger until the characteristic cauliflower shape resulted. The reason for the formation of such rosettes is obscure, but it is a fact that fractured fossils or pieces of chert will develop areas of rosette quartz along the fractured zones if subjected to the influence of silica-bearing waters. All of the chert at the top of the Beekmantown has not undergone secondary silici- fication into the cauliflower form. Fragments of platy chert representing the primary silicification stage may occasionally be noted with fracture zones penetrating into or entirely through them. The water with silica in solution will seep into these fractures and deposit the silica there first, thus starting a growth area which develops into the characteristic rosettes of the cauliflower variety. By this process a small fragment of platy or irregular chert by continual growth of the rosette areas will develop into specimens of the cauliflower variety a foot or more in diameter.

Apparently the same process occurs in fractured fossils found in cer- tain siliceous shale formations, particularly of Silurian and Missis- sippian ages. For example, a crinoid column of say one-half inch in diameter, exposed to silic'a-bearing waters, will first receive a deposit of silica in its central canal and rosettes of silica will project from each end. The column is fractured by this process and each fracture line then

MARYLAND GEOLOGICAL SURVEY

CAMBRIAN AND ORDOVICIAN, PLATE XVI

FlG. I. — NEAR VIEW OF BEEKMANTOWN LIMESTONE AT LEGORE QUARRY, LEGORE, MARYLAND. STRATA PENETRATED BY A SIX-INCH DIABASE DYKE (MARKED BY HAMMER).

FlG. 2. — VIEW OF CONTACT BETWEEN THE BEEKMANTOWN (B) AND STONES RIVER (s) LIMESTONES ALONG THE SOUTH SIDE OF THE NATIONAL HIGHWAY AT WILSON, MARYLAND. THE ZONE OF CAULIFLOWER CHERT (c) IS WELL DISPLAYED AT THIS PLACE.

MARYLAND GEOLOGICAL SURVEY 109

becomes filled with silica which, with continual deposition, enlarges the original small column into a mass several inches in diameter. Usually in such cases the resulting mass is hollow and lined internally with crystals, thus forming a geode. Sometimes, however, it is solid, in which event a structure not unlike the cauliflower chert results.

The general problem of silicification is most complicated and little is known yet of either its chemical or physical aspects. Why a certain limestone should, under past or present-day weathering, develop chert products which are so alike over large areas that they can be used in the determination of the bed, is not only an interesting question scientifically, but it is also of such geological importance as to merit the most detailed study.

Another interesting feature in connection with the cauliflower chert is its occurrence, noted at several places, in a black shale, sometimes regu- larly bedded but again irregularly deposited, much resembling an ancient soil. Such a shale bed at the top of the Beekmantown may be seen in the cut along the National Highway just west of Wilson, Md. Cauliflower cherts are very abundant in this shale bed and its surface outcrop strews the ground with the irregular masses. However, they are not limited to this shale, for here, as well as at other places, the typical chert occurs in regularly bedded dolomite.

Although discussed here in connection with the Beekmantown, the zone of cauliflower chert, if the above explanation is correct, should be regarded as basal Stones River. It might in reality be regarded as a basal con- glomerate formed, however, in a totally different manner from other conglomerates.

AREAL DISTRIBUTION. — The Beekmantown limestone with its basal Stonehenge member is the most widely distributed early Paleozoic forma- tion in Maryland, as its outcrop covers large areas in both the Appalachian and Frederick valleys where its strata weather rapidly into good soil and produce a gently rolling country with excellent farm land.

In the eastern belt of outcrop in the Appalachian Valley the formation is closely folded, occupying an area equal to half that of the Valley and

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110 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

extending from a line passing through Security, three miles east of Hagerstown, to a northeast-southwest line west of Williamsport where a fault brings the limestone in contact with the Martinsburg shale. The broad expanse of Conococheague limestone in southern Maryland reduces •the width of the Beekmantown here from a belt almost seven miles wide at the Pennsylvania state line to less than three at the Potomac. South of Hagerstown the Conococheague and Beekmantown limestones are intimately folded together, exhibiting characteristic Appalachian pitch- ing anticlines and synclines. The western edge of this belt is a fault line except at the extreme northern and southern ends where the normal sequence is resumed. This fault is clearly shown at Williamsport where the middle limestone of the Beekmantown may be seen in contact with the lower Martinsburg shale. North of Williamsport the displacement of this fault is greater and brings the Beekmantown in contact with the upper sandy portion of the Martinsburg. Infolded in this large area 01 Beekmantown are elongated, narrow bands of the purer limestones of the succeeding Stones Eiver formation.

In the area west of the Martinsburg shale plateau the Beekmantown limestone likewise occupies about one-half of this part of the Appalachian Valley, but here closely folding with the Conococheague limestone causes each formation to appear at the surface in elongated, more or less parallel bands. The continuity of these bands is broken in the northern part of the state by a transverse fault. West of the eastern base of North Mountain no rocks of Beekmantown age are exposed.

The surface rock of a considerable portion of the Frederick Valley belongs to the red beds of Triassic age, but of the limestone portion of the valley about one-half is occupied by strata referred to the Beekman- town. These Beekmantown areas occupy in general the eastern half of this portion, although folding brings small areas to the surface in the western half. Two small areas just east of Catoctin Mountain are of interest because erosion of the red beds has proceeded far enough to expose the underlying Beekmantown strata.

MARYLAND GEOLOGICAL SURVEY 111

East of the Frederick Valley on the Piedmont Plateau, narrow, elon- gated, infolded areas of limestone occur, only one of which is shown on the map because of its evident relationship to the limestone of the valley proper. Metamorphism has destroyed the evidence as to the age rela- tions of these limestones, although it is possible that they represent an eastern extension of the f ossilif erous Beekmantown strata .of the Frederick Valley.

FREDERICK VALLEY LIMESTONES

The considerable development of Early Paleozoic limestones east of Catoctin Mountain in the Frederick Valley and their economic value has long been known to geologists. As these deposits occur east of the Blue Ridge and are the easternmost unmetamorphosed Paleozoic strata known, the determination of their exact age relations is a matter of importance and interest. The Frederick Valley is bounded on the west by Catoctin Mountain, composed of Lower Cambrian sandstone and shale, and on the east by a range of low hills formed by pre-Cambrian schist. The length of the limestone area is about 30 miles and its maximum breadth about six miles. North of LeGore, Maryland, the limestones pass under cover of the Newark red beds, while at the Potomac they cross into Virginia where they again soon disappear under the red beds.

This area has been studied by several geologists, but the most important work upon it was that of Keyes, who published his results in 1890 in the Johns Hopkins University Circular. His description of these rocks is as follows : " The beds have a mean dip of about 25 degrees to the east- ward. Along their western border they are covered by Triassic red sand- stones (Newark formation). To the east the limestones pass gradually into shales and slates, the whole forming apparently a conformable series. The limestones in great part are bluish in color, compact and heavily bedded ; but on approaching the shales they become more and more thinly bedded and very dark blue or nearly black, owing to the bituminous matter present. The latter, however, is driven off by burning, leaving a pure white lime. In places this lime rock is highly siliceous on account of the presence of a considerable amount of rather coarse quartz sand.

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112 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

This large amount of silica renders the rock unfit for the manufacture of lime, which at present is the chief use to which the Frederick Valley limestones are put. From the thin-bedded belt the limestone passes into a more earthy facies and grades into dark colored calcareous shales and these again into slates or into sandy shales."

7T,

FlG. 12. STRUCTURE SECTIONS ACROSS FREDERICK VALLEY.

A. Devilbiss Bridge east through McAleer.

B. Braddock Heights east through Frederick.

C. East-west section through Frederick Junction.

D. East-west section through Buckeystown.

Tn — Newark sandstone and shale. Tnc — Newark conglomerate. Ob — Beekmantown limestone.

SYMBOLS.

Of — Frederick limestone.

Ch — Harpers shale.

Cw — Weverton sandstone.

Ol — Loudon formation, Ac — Catoctin schist.

Keyes found a few species of fossils in these limestones which led him to suggest that the whole series was equivalent to the Chazy, Trenton, and Hudson River formations. The determination of the age and structure relations of the Frederick Valley limestones was a matter of

MARYLAND GEOLOGICAL SURVEY 113

some difficulty, and the present author was fortunate in having this earlier work upon the subject even though he is unable to agree with some of the conclusions. Comparison of the four structure sections across the Frederick Valley, here presented as fig. 12 with that published by Keyes, will show that the present conception of the structure and stratigraphy differs radically.

The lowest sedimentary rocks of this particular region are comprised in the Lower Cambrian quartzites, the Weverton sandstone and the succeed- ing Lower Cambrian Harpers shale exposed in Catoctin Mountain. Sugar Loaf Mountain, on the east, likewise is composed of Lower Cambrian quartzite. In the opinion of the writer the limestone series does not pass upward on the eastern side of the valley into Hudson River shales, but it is faulted against shales and schists which are of pre-Cambrian age. Along the western side of the Frederick Valley the limestones are covered by the conglomerate, red sandstone and shale of the Newark series except in two areas where stream erosion has cut deeply into and in places almost to the base of the underlying limestones.

The structural relations of the Frederick Valley are so complicated that it would be difficult to unravel the stratigraphy were it not for the occa- sional presence of fossils. Determinable, though but rarely preserved, fossil remains have been noted at numerous places in the valley in two distinct kinds of rocks, namely, in dark blue thin-bedded strata, known locally as the building rock, and in massive, rather pure, blue to white limestone that is quarried for lime. The fossils in the quarry rock have been found distributed through several hundred feet of strata. They consist mainly of cephalopod shells which are closely related to lower Beekmantown species. The fauna found in the building rock consists of a brachiopod and a trilobite of types which are unquestionably of post Beekmantown age. By fossil evidence, therefore, the age of the quarry rock is established as older than the building rock. This conclusion is borne out also by the structural relations of the beds, the building rock being invariably infolded in the quarry rock. In all probability, the line of contact between the limestone which forms the floor of the valley and

114 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

the siliceous formations which form its elevated east and west boundaries, is in both cases a fault plane. There is little doubt as to the faulting on the east side, but the evidence is not so convincing on the west side. The succession there may be normal, that is, undisturbed with the Beekman- town limestone lying unconformably on the Lower Cambrian Harpers shale.

The Beekmantown Limestone

All of the numerous quarries in the Frederick Valley operated for the burning of lime expose massive, rather pure, bluish limestones which hold fossils of Beekmantown age. The rock itself is not unlike that of the lower Beekmantown above the Stonehenge member in the Appalachian Valley, so that the use of the name Beekmantown for the quarry rock seems appropriate. It is even possible that the Stonehenge member is represented here, for in the outcrops of Paleozoic limestone in the western part of the valley, namely, along the trolley car track two and one-half miles northwest of Frederick, strata with edgewise conglomerates are well developed. Usually, in this part of the valley, these massive limestones are covered by Mesozoic red beds. However, in two places, erosion has removed the red beds so as to expose not only the quarry rock, but also the underlying Harpers shale. One of these is in a small area two miles south of Catoctin, the other a larger exposure just east of Braddock. Fossils were not observed in either of these areas, but the lithology of the limestone is precisely like that of the fossiliferous strata a short distance to the east. Moreover, as shown on the map (pi. I), an area of quarry rock just east of Braddock contains an infolded band of fossiliferous building rock. Throughout the central and eastern parts of the valley where the quarry rock frequently outcrops there can be no question regarding the Beekmantown age, for here fossils are not uncommon. Along the eastern edge of the valley just west of the pre-Cambrian schists there are outcrops of a massive light gray laminated limestone in which the laminae are much contorted and weather into a sandy shale somewhat resembling the shale fragments resulting from the disintegration of the upper Stone- henge member of the Beekmantown. Fossils have not been discovered in

MARYLAND GEOLOGICAL SURVEY 115

these particular beds, but these laminated strata undoubtedly represent a part of the Beekmantown as developed in the Frederick Valley.

The northernmost exposures of the Frederick Valley limestones occur at LeGore, Maryland, just before these strata disappear under the red beds. Extensive quarrying operations here have exposed a considerable section of closely folded and evidently repeated beds. The clue to the proper sequence is given by several bands of the normally overlying thin- bedded f ossilif erous building rock that are infolded with the more massive Beekmantown limestones.

At LeGore the building rock is immediately underlaid by about 100 feet of massive dark blue rather pure limestone in beds two to three feet thick, alternating with similar beds of lighter colored strata. Cephalo- pods of Beekmantown affinities are not uncommon on the weathered edges of these strata. These upper fossiliferous beds are separated by about 50 feet of massive light blue limestone with quartz grains, from a lower fossiliferous zone. This comprises several hundred feet of strata similar in lithology and fossils to the upper beds. The section then continues for several hundred feet which appear to be a repetition by folding of the strata just described. Many of these massive beds are very homogeneous and marble-like in character. The quarries at Frederick and to the south also afford excellent exposures of the upper beds of the massive lime- stone, but as the strata are little folded here, the exposed thickness is consequently slight. On account of their ready solubility, outcrops of these pure massive limestones appear only in lowland areas. They also leave no surface residual products such as the quartz or shale fragments of the building rock.

The Frederick Limestone

This new name is proposed for the strata in the Frederick Valley over- lying the Beekmantown limestone and containing a fauna probably of Chazyan age. The rocks are shown to advantage in numerous quarries and natural outcrops around Frederick. Fossils are of rare occurrence in these outcrops, but they may be found occasionally in the broad, thin slabs of which the stone fences of the valley are built.

116 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND

The Frederick limestone consists of thin-bedded dark blue argillaceous strata separating into layers usually less than two inches in thickness. On further weathering, these leave as a residual product in the soil, brownish-yellow shale-like fragments quite similar to the weathered Martinsburg shale of the Appalachian Valley. This limestone is often much crumpled and so seamed with quartz veins that the disintegration of its strata leaves numerous fragments of white crystalline quartz in the soil. In freshly quarried exposures the Frederick limestone appears massive and dark blue, but slight exposure to the weather causes its separation into the thin flagstones so much used in this area for building fences and embankments that the local name of building rock is applied to it. It is less soluble than the associated purer Beekmantown limestone, so that in weathering it gives rise to hill topography which is in marked contrast to the lowland areas characteristic of the Beekmantown strata. The dark-blue color, thin platy . layers of argillaceous composition, upland topography and residual quartz fragments distinguish it readily from the lighter colored, massive, purer rock referred to the Beekmantown.

Although numerous exposures of the Frederick limestone may be seen in the vicinity of Frederick, perhaps the best place to view its contact with the underlying Beekmantown limestone is at the Tabler quarry where a distinct line of unconformity may be noted between the two formations.

The thickness of the Frederick limestone is difficult to determine because it has no recognizable upper boundary such as the succeeding formation. However, in areas where it is infolded into the Beekmantown limestone, its thickness seems to be not less than 200 feet. Such infolded areas are well shown in the quarries at LeG-ore, Maryland.

Although of rare occurrence fossils can be found in this limestone more frequently than in the subjacent strata because the opportunities for collecting are more numerous. The natural outcrops of the rock seldom show organic remains, but it is only a matter of search along the stone fences of the Frederick Valley to discover fossils in the thin lime- stone layers of which most of them have been built. Five species have

MARYLAND GEOLOGICAL SURVEY 117

been noted, only two of which are sufficiently preserved for specific description. These are Acidaspis ulrichi and Strophomena stosei, two new species and an undetermined species each of the genera Reteocrinus ?, Cameroceras and Isotelus. The prime interest of this fauna, like that of the underlying Beekmantown, is in its occurrence east of the Blue Ridge. This particular association of species is also noteworthy because neither the fauna itself nor the beds containing it can be correlated directly with any Appalachian Valley formation. However, the fauna suggests a Chazyan or early Mohawkian age with the possibility more in favor of the former.

THE STONES RIVER LIMESTONE

The purest limestones of the Shenandoah series are contained in the strata occurring between the underlying finely laminated pure and magnesian Beekmantown formation and the overlying argillaceous nodular Chambersburg limestone of Black River age. These pure lime- stones are correlated on lithologic, stratigraphic, and paleontologic grounds with the Stones River group or formation of the Central Basin of Tennessee. In Maryland the Stones River limestone rests unconform- ably upon the Beekmantown, the uneven contact being well marked by an extensive development of secondarily silicified chert known as " cauli- flower " chert.

The Stones River was named and defined as a distinct group in 1855 by Safford, who based