DEPARTMENT OF THE INTEEIOE

BULLETIN

OF THE

GEOLOGICAL SURVEY

No. 134

WASHINGTON

GOVERNMENT PRINTING- OFFICE 

1896

UNITED STATES GEOLOGICAL SUEVEY

CHARLES D. WALCOTT, DIKECTOB

THE

CAMBEIAN EOCKS

PENNSYLVANIA

BY

CHADLESS DOOLITTLE WALCOTT

WASHINGTON

GOVEENMENT PRINTING OFFICE 

1896

CONTENTS.

Introduction ......................................................._....;.... 9

York County................................................................. 11

South Mountain............................................................. 19

Lancaster, Berks, and Lehigh counties....................................... 28

Northern belt of limestone.................................................. 29

Correlation ................................................................. 31

Tntraformational conglomerates ............. ....".. ........................... 34

Definition of term and illustrations................................:..... 34

Canadian localities...................................................... 34

Vermont and New York localities........................................ 35

Pennsylvania localities.................................................. 36

Virginia localities....................................................... 37

Tennessee localities..................................................... 37

Origin.................................................................. 39

Mode of formation of thin-bedded breccias............................... 40

Index....................................................................... 41

5

ILLUSTRATIONS.

Page. 

PLATE I. Geologic sketch-map of southeastern Pennsylvania ................ 8

II. Central portion of the Chickies quartzite at Chickies Rock, on the

Susquehanna Eiver, Lancaster County, Pa...................... 12

III. Banded Lower Camhrian rocks, one-fourth mile southwest of Emigsville, York County, Pa.......................................... 16

IV. Illustration of erosion by solution beneath the soil of a massive bed

of Lower Cambrian limestone at York, Pa....................... 18

V. Synclinal fold in the thin-bedded Lower Cambrian limestone in

the suburbs of York, Pa......................................... 20

VI. Cliff of massive-bedded Lower Cambrian limestone on the line of

the Pennsylvania Railroad, at Bellemqnt, Lancaster County, Pa.. 28

VII. Lower Cambrian limestone exposed in quarries at Bellemont, Lancaster County, Pa ........:..................................... 30

VIII. Massive-bedded, light-gray, siliceous limestone in quarries onefourth mile north of Pennsylvania Railroad tracks, Bellemont, 

Lancaster County, Pa........................................... 30

I.. View of old limekiln at Bellemont, Lancaster County, Pa.......... 32

X. Brecciated limestone conglomerate in Lower Ordovician southeast of

Highgate Springs, Franklin County, Vt......................... 34

XI. Exposure of limestone conglomerate in Lower Cambrian limestone

at York,Pa..................................................... 34

XII. Conglomerate limestone one-fourth mile north of Stoners Station,

York and Wrightsville Railroad, York County, Pa............... 36

XIII. View of a bowlder in the thin-bedded limestone between the beds 

of limestone conglomerate at a quarry one-fourth mile north of 

Stoners Station, York and Wrightsville Railroad; York County, Pa. 36

XIV. Nearer view of the bowlder shown in PI. XIII, seen from a different

direction ....................................................... 38

XV. Brecciated layer of fine sand and silt produced by tbe inflowing tide 

breaking up the layer hardened by sun and wind on tidal flat in 

inlet west of Noyes Point, R. I .................................. 40

7'

U.S.GEOLOGICAL SURVEY. BULLETIN N? 134. PL.I.

GEOLOGIC SKETCH MAP OF SOUTHEASTERN PENNSYLVANIA

AFTER SECOND GEOLOGICAL SURVEY OF PENNSYLVANIA .

JUI-iUS BICN a C

MF.SOZOIC SILURIAN (ORDOVtCIAN)

1 j SILURIAN (ORDOVICIAN ) 

J (CAMBRIAN (LIMESTONE)

CAMBRIAN (QUARTZITE)
THE CAMBRIAN BOOKS OF PENNSYLVANIA.1

BY CHARLES D. WALCOTT.

INTRODUCTION.

Prior to 1892 the strata in Pennsylvania referred to the Cambrian 

system included the Primal Quartzite of Professor Bogers, and Prof. 

J. P. Lesley was inclined to consider the sandstone and slate of the 

South Mountain proper as of Cambrian age. The line of outcrop of 

the Primal Quartzite extends along the boundaries of the various 

Archean areas from the Delaware Eiver on the northeast, in Backs, 

Lehigh, and Northampton counties, southwesterly, with more or less 

interruption, across Berks, Montgomery, Chester, Lancaster, Lebanon, 

York, Cumberland, Adams, and Franklin counties to the Maryland 

line. Prof. J. P. Lesley's summary of the formation is as follows:

The lowest Paleozoic formation in Pennsylvania, No. 1, logically identified with 

the Potsdam sandstone of northern New York, makes its appearance along the edges 

of the limestone No. II at the north foot of the Azoic mountain range between Bethlehem and Reading, in Lehigh and Berks counties; in Mulbaugh Hill, on the Lebanon 

county line; in Chicques ["Chickis" of Frazer] Ridge, on the Susquehanna, above 

Columbia; in the Welsh Mountain, in northern Chester; and in the North'Valley 

Hill, which stretches for 60 miles from the heart of Lancaster to the Bucks-Montgomery county line, north of the city of Philadelphia. Its only fossil as yet discovered is a Scolithus, but its position next beneath the Calciferous limestone is too well 

marked to admit of doubt. Formerly it entirely covered the mountain districts north 

and south of the Schuylkill Eiver, because it still spreads in sheets upon their sides, 

and in many places makes their summits, lying unconformably npon the gneiss.

The South Mountains proper, which separate Cumberland from York and Franklin 

from Adams County, do not thus exhibit the fundamental gneiss covered by a coating of Potsdam, but are composed of peculiar sandstone and slate strata several 

thousand feet thick, which occupy the place of the Potsdam in the series, but can not 

certainly be identified with it. They may be considered the equivalents of the 

Ocoee and Sewanee strata of East Tennessee. * * * We may consider our South 

Mountain rocks, therefore, those lying north of the tu-rnpike fault, as of Cambrian

1 The object of this paper is to place on record certain observations made during the summers of 

1892 and 1893. These observations embraced the belt of Lower Paleozoic rocks lying between the 

Delaware and Susquehanna rivers and the Potomac Eiver.

8 A geological hand atlas of the sixty-seven counties of Pennsylvania embodying the results of 

the field work of the survey from 187* to 1884; Second Geol. Snrv. Penn., Keport of Progress X, 1885, 

pp. zvi, xvii.

9
10 CAMBRIAN ROCKS OF PENNSYLVANIA. [BULL. 134

The Primal Quartzite is correlated with the Potsdam sandstone of 

'New York in Lehigh and Northampton counties, and is described by 

Mr. Frederick Prime, jr., as "a hard, compact quartzite, of a yellowish 

color where weathered, and, when freshly quarried, of a grayish tint. 

* * * The thickness, where it could be measured, was 21 feet." l

The quartzite varies in thickness from 20 to 300 feet, the greater 

thickness being in the Chickies 2 section of Lancaster County, where, 

according to Dr. Persifor Frazer, it reaches 300 feet. Southwest of 

the Susquehanna Eiver it is difficult to measure its exact thickness, 

owing to complications resulting from faulting and folding and the 

absence of clearly exposed sections. The character of the formation 

throughout the State is quite uniform, and the only traces of organic 

remains that had been found previous to my investigations were the 

straight, vertical tubes of Scolithus.

In a summary of the Cambrian rocks of Pennsylvania which I published in 1891, occurs the following: 3

Prof. H. D. Rogers referred a series of slates between the sandstone called Potsdam and the base of the superjacent limestone to the Primal period, but the geologists of the Second Geological Survey consider them as belonging to the limestone 

series. If a comparison be made with the Tennessee sections, where the schists and 

shales between the quartzite and the. limestone are characterized by Cambrian 

fossils, this series of schists will certainly be referred to the Cambrian, as it is subjacent to the great limestone series and superjacent to the quartzite. Professor 

Rogers described the highest of the Primal newer elate as a "greenish and bluish 

talcose argillaceous slate, sometimes very soft and shaly, and with a thickness of 

about 700 feet." Dr. Frazer refers about 1,600 feet of "Hydromica-schist" to the 

interval between the quartzite and limestone in York County.4

The upper part of the Primal slates does not appear to be developed to the northeastward in Lehigh, Northampton, Bucks, Montgomery, Berks, and Chester counties. 

It first appears with any considerable thickness in Lancaster County, near the Susquehanna River, and south of the quartzites of the Chickis Hills. Thence it extends 

southwesterly across York and Adams counties to the Maryland line, increasing in 

thickness in Maryland and Virginia.

As a whole, the Cambrian system in Pennsylvania appears to be represented by 

the lower quartzite and the superjacent shales and schists as originally denned by 

Professor Rogers, and it may be that the lower portion of the superjacent limestone 

will be included.

In a letter from Professor Lesley, dated May 8, 1890, he says:

"Reading Ells's paper and Brainerd and Seely's paper in Bull. Geol. Soc. America, 

just published, with your remarks at the meeting, I naturally reverted to my South 

Mountain surveys (twenty years ago) east of Chambersburg, Pa. (Fulton and Adams 

counties), and the strange and powerful impression made on me then by the outcrop 

of alow ridge of purple shales running from the pike.southward, just back (east) 

of the western mountain ridge. I never saw anything like them, and feel strongly 

inclined to consider them the Sillery purple shales (Cambrian) of the North. I can 

not find or remember any description of this outcrop by Frazer. It lies in Fulton 

County, outside the Adams County line."

1 Geology of Lehigh and Northampton counties: Second Geol. Surv. Penn. D3, Vol. 1,1883, p. 205. 

s This is the spelling adopted by the United States Board on Geographic Names. 

»Bull. TJ. S. Geol. Surv. No. 81,1891, p. 289. 

'* General notes Sketch.on the Geology of York County, Pa.: Am. Philosoph. Soc., Proc., Vol.

xxm, use, P. 401.
WALCOTT.] YORK COUNTY. 11

In his report on the Geology of Pennsylvania,1 Professor Lesley 

summarizes his opinion upon the geology of the South Mountains and 

Formation No. 1. In this, Formation No. 1 js referred to the Upper 

Cambrian, and a detailed description is given of its occurrence along 

the South Mountains and across the State to the Delaware. The superjacent limestone, No. 2, is referred to the Ordovician.2 Fuller reference 

will be made to Professor Lesley's descriptions in speaking of .the rocks 

of York County.

During the summer of 1892 I made an examination of the Cambrian 

rocks between the Susquehanna and the Potoinac, and during the field 

season of 1893 followed it by a rapid reconnaissance of a portion of 

the area between the Susquehanna and the Delaware, for the purpose of 

determining whether the lower quartzites with their super] acent limestones were of the same geologic age as the quartzites southwest of 

the Susquehanna. When I took up the work, after an examination 

of the published literature, including geologic sections and maps, I 

decided to begin the investigation in York County, along the Susquehanna, as the section there and about the Hellam Hills appeared to be 

less disturbed and to present more favorable conditions for obtaining 

good results'than the area to the southwest.

YORK COUNTY.

On the map of the First Geological Survey of Pennsylvania 3 the 

area now under consideration in York County was included under the 

colors of the '''Primal sandstone" (Potsdam) and the Auroral limestone, the latter being equivalent to the Black Eiver-Chazy limestone 

and Calciferous sand-rock of the New York section, as explained in the 

key to the geological map.

During the progress of the Second Survey Dr. Persifor Frazer, jr., 

was placed in charge of the survey of York and Adams counties. On 

his map of York County, published in 1879, the formations under consideration are subdivided more than on the Eogers map of 1858. They 

are bounded on the north by the Mesozoic u New Red" sandstones, 

and on the southeast by "Azoic slates, etc.," and consist, in descending 

order, according to the legend, of 

4. Limestone (Silurio-Cambrian?). 

3. Hydrdmica-schists, etc. 

2. Quartzite (Potsdam?). 

1. Chlorite schists, etc.

.In the report of progress for 1874-75, Dr. Frazer states that the 

schists (3) carrying the iron ore do not belong to the Auroral limestones, but to a series of schists beneath, -and that there is, probably,

1 A Summary Description of the Geology of Pennsylvania, Vol. 1,1892, chapters .15 and 16. 

9 Loc. cit., p. 307. 

 Henry D. Eogers, 1858.
12 CAMBRIAN BOOKS OF PENNSYLVANIA. [BULL. 134.

a line of unconformity between the limestones and the subjacent 

" Crystalline schists." l

In discussing the question of the contemporaneity of the schists with 

the limestones called by Dr. Bogers the "Auroral," he concludes that 

two questions are involved: "First, are two limestones of different 

ages confounded under the name of <Auroral;' second, if so, are they 

conformable the one to the other?" He decided that the crystalline 

schists containing the ore bodies seem to form the floor on which the 

York limestone lies, while another limestone seems to be bedded with 

them.2 Mention is also made of a limestone conglomerate consisting 

of a blue limestone holding rounded pebbles of white limestone within 

it, that occurs in a quarry half a mile north of the Columbia Bridge.3

The preceding is quoted to show that Dr. Frazer had a conception 

that there is a limestone beneath the York limestone, embedded in the 

unconformably subjacent schists, that is not of the same age as the 

"Auroral" limestones, which .were referred to the Chazy-Calciferous 

horizon by Eogers and others. The evidence for this is materially 

weakened by the statements contained in his report on Lancaster 

County, that the Lancaster limestone 

 * * has great masses of hydro-mica schists, argillites, rhomboidal slates, and 

gray, weathered, leached-out pyritiferous strata. * * * Slates and argillites, and, 

perhaps a little more rarely, true hydro-mica rocks may come into any horizon of the 

limestone. * * * This intercalation of foreign beds does not seem to he at present 

redncible to any rale, though in general such transitions seem to be more frequent 

in the lower than in any other parts of the measures.4

He considers the Lancaster limestones as probably the equivalent of 

the Calciferous and Trenton limestones of the New York series, and 

mentions that the York limestone is a slender offshoot.5 The Hellam 

quartzite of York is called the "Chikis" quartzite, and is described 

as a basal formation upon which a series of schists occur that to the 

south "are, at all events, those slates in which the iron ores of Lancaster and York are invariably found the transition series between 

the 'Primal and Auroral.'" 6 In his final report,7 Professor Lesley 

describes the "Chiques" sandstone as the same formation as the Hellam quartzite of York County (as named by Frazer) and equivalent to 

the Upper Cambrian quartzite of Walcott. He prefers to use the older 

name "Chiques" for these sandstones, stating that it is best to get rid 

of the old name "Potsdam" sandstone, as there does not seem to be 

any satisfactory evidence that the proper Potsdam sandstones of the 

Canada line and Lake Champlain extend as far south as southern

"Second Geol. Surv. Penn., Keport of Progress in the District of York and Adams counties, 1876, 

p. 130.

2Loc. cit., pp. 132, 134.

»Loc. cit., p. 132.

«Seoond Geol. Surv. Penn., Report of Progress in 1877, Geol.. of Lancaster County, 1880, p. 5.

 Loo. cit., p. 4.

 Loc. cit., p. 7. .

'Qeol, Surv. Penn., Summary Description of the Geology of Pennsylvania, Vol. 1,1892, p. 165.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 134- PL. II

CENTRAL PORTION OF THE CHICKIES QUARTZITE AT CHICKIES ROCK, ON THE SUSQUEHANNA 

RIVER, LANCASTER COUNTY, PENNSYLVANIA.
WALOOTT.] YORK COUNTY. 13

Pennsylvania. He says that the section at "Chiqnes Bock" is not 

quite comprehensible at one or two points. I found that it is so complicated by the folding of the strata and by thrust-faulting that it is not 

a typical section. It exposes, however, the lowest of the Cambrian now 

known to me in central Pennsylvania. The quartzite at "Chiques 

Bock," near Chickies, is the Scolithus quartzite, and is stratigraphically 

at the summit of the series of quartzites and slates forming the 

"Chiques Bock" section, although apparently at the base in the section, owing to the disturbance of the strata. The quartzites and slates 

to the south, between "Chiques Bock" and the limestones at Columbia, 

are older, and have been raised up from beneath and thrust over on the 

Scolithus quartzite at " Chiques Bock." This is determined by the succession shown in the section exposed on the flanks of South Mountain, 

in Franklin County, west of Monterey, reference to which is made in 

the notes on the geology of South Mountain.

In relation to the stratigraphic position of the slates, etc., beneath 

the .Lancaster limestone, I will quote the statement of Professor Lesley:

The geographical proof that the slates overlie the quartzite is complete, and establishes the correctness of Professor Rogers's "Upper Primal slate formation." The 

geological evidence is equally conclusive; for the general dip of the Chiques rock is 

southward, under the slates; and of the slates southward under the limestone.'

The exposure of the Chickies Quartzite at Chickies Bock, on the 

Susquehanna, is remarkably fine. It rises in a bold bluif 100 feet or 

more in height, forming a low anticline with a slight synclinal depression near the center. Nearly vertical cleavage planes extend from top 

to bottom through many of the layers in the central portion. This is 

shown in PI. II.

The continuation of "ChiquesBock" to the westward, in York County, 

forms the Hellam Hills,2 and shows a broad anticline of quartzite surrounded by schists. Numerous sections along the southern and western 

sides of the Hellam Hills show that the quartzites pass beneath a series 

of shales, slates, and sandy and calcareous layers, which, in turn, pass 

beneath the limestones of the valley.

It was my good fortune to have the acquaintance of Prof. A. Wanner, 

superintendent of public schools at York. He volunteered to be my 

guide to localities where he knew there were good exposures of the 

quartzites, schists, and limestones; and he accompanied me for a week.

The study of the rocks in York County was begun under the impression that the limestone was the "Auroral" limestone of Bogers, and 

equivalent to the Chazy-Calciferous of the New York section. I thought, 

however, that there was a probability of its being Cambrian in age, 

from the fact that in Tennessee, Yermont, and New Jersey the lower

»Loc.cit.,p.l72.

*I did not learn, when in York County, of any local name for this ridge of hills, and as most of the 

ridge ia within the township of Hellam I shall speak of them as the Hellam Hills.
14 CAMBRIAN BOOKS OF PENNSYLVANIA. iucLL.134.

portion of the great limestone series above the quartzite and shales, 

is undoubtedly of Cambrian age.

A reconnaissance was first made of the section at tl Chiques Bock," 

thence south to Columbia, Pa., and then on the western side of the river 

from Wrightsville north to the quartzites. A careful study of the 

" Chiques Eock " section led me to think that there was a considerable 

disturbance and a complication of the normal section, by ovefthrust of 

the lower beds upon the higher, between the Scolithus quartzite at 

" Chiques Eock" and the limestone at Columbia. On the western side 

of the river the section appeared to be unbroken from the Hellam Hills 

to Wrightsville, and to be as represented by Dr. Frazer in his section 

along the right bank of the Susquehanna. l In this the succession is 

from the quartzite (1) to the shales (2) and to the limestone (3), in 

Wrightsville, at Columbia Bridge. The sandy shales and argillites (2) 

pass conformably beneath the massive limestone (3), which forms a 

deep synclinal fold before being cut off to the south by a fault.

The second section examined was No. 2 of Dr. Frazerrs, extending 

from Emigsville south through Eed Lyon Station. 2 In the description 

of this section 3 he refers the sandstone in the railroad cut just north of 

Emigsville to the Triassic New Eed sandstone. At the northern end 

of the cut he noted a fine-grained sandstone dipping W. 15°, K. 52°. 

To the southward of this he describes a calcareous, sandy, pink shale 

dipping S. 5°, E. 20°. This is subjacent to 27 feet of blue, finely laminated limestone, with white streaks, upon which rests a red bed of 

calcareous conglomerate 2 feet thick; this, in turn, is subjacent to a 

belt of reddish, shaly sandstone, 63 feet in breadth, and a compact, 

fine-grained sandstone, 9 feet in thickness, which is capped by 166 feet 

of arenaceous shales of a somewhat flaggy character.

Dr. Frazer says:

There would seem to be, therefore, an anticlinal in the Triassic measures the only 

instance of one recorded within the limits of this district. The contact line of 

limestone and Mesozoic sandstone lies within or just north, of the town of Emigsville. The first recorded dip in the older formation when projected upon the line of 

section is 2,160 feet, or a little more than a third of a mile from the last dip. 4

I mention the details of Dr. Frazer's section because it is the one 

which led to the determination of the stratigraphic position of the 

Chickies quartzites and the York shales, 5 which are subjacent to the

'Second Geol. Surv. Penn., 1876; section 1 accompanying Report of Progress in the district of 

York and Adama counties for 1874.

5Loc. cit., section 2.

«Loc. cit., p. 88.

«Loc. cit.,p. 89.

5The name " York shales " is proposed for the band of shales resting upon the quartzites surrounding the Hellam Hills. It is particularly well developed in York County, but appears to be absent in 

many of the sections about South Mountain and about the same series of quartzites in Lancaster 

County.
WALCOTT.J YORK COUNTY. 15

Lancaster limestone. 1 The fault between the Paleozoic (Lower Cambrian) rocks and the New Bed sandstone of the Mesozoic occurs in the 

railroad cut at the point indicated in Dr. Frazer's section as the crest 

of an anticline in the New Red sandstone. l3o such anticline exists. 

The southern leg of Dr. Frazer's anticline is formed of rocks that bear 

no resemblance to the Mesozoic Eed sandstone, and fossils of Lower 

Cambrian age are abundant in the 9 feet of compact, fine-grained 

sandstone described by him. The section, from the fault line southward, is as follows:

Section from Emigsville south through Bed Lyon Station, Pa. Thickness

in feet.

1. Gray, banded, and mottled limestones, with purplish bed of limestone at 

summit 3 feet thick. Strike, E. and W. (mag.); dip, 25° S. This limestone weathers into a more or less arenaceous shale..................... 33

2. Gray and buff sandy shales passing (at 21 feet) into shaly sandstone and 

then into sandy shale, where a belt of calcareous quartzite occurs in 

layers varying in thickness from 2 to 12 inches. Fossils: Camarella

minor, and fragments of Olenellus showing portions of the head and thoracic segments 9 ........................................................ 105

3. From the fo_ssiliferous beds just mentioned, for a distance of 500 feet, the 

hillside on the east side of the railroad is covered with the debris of sandy 

shales, and several exposures occur along the roadside. From the last of 

these to the first outcrop of limestone, a distance of 250 feet, the debris 

of sandy shales and thin-bedded calcareous quartzite occur abundantly 

in the southward-facing hill slope. Fossils: Numerous fragments of 

Olenellus and casts of Camarella minor occur in the calcareous quartzite 

interbedded in the shale. As the last observed dip was 25° S., it is 

assumed that the section is unbroken, and a thickness is assigned to this 

division of..............................................'............... 315

4. Massive-bedded, dove-colored, banded limestones. Strike, N. 20° W. (mag.); 

dip, 25° S. 3 Although the section is more or less concealed by soil, numerous outcrops occur in quarries to the south. These show a banded limestone in the lower portion of the section, with numerous irregular, small, 

concretionary bits of limestone, usually elongated with the bedding plane. 

The average dip of the bed is from 20° to 25° S.° A beautiful section is 

shown in a quarry about one-fourth of a mile east of Emigsville, and in a 

quarry on the turnpike west of the railroad, in the outskirts of the town. 

A little higher up in the section the limestones are massive, light-colored, 

and, in places, almost a crystalline marble.

At a quarry in a field east of the railroad track and near where the road 

turns to the eastward toward Cpdorus Creek, the strike of the limestone is 

N. 15° W. (mag.), and the dip 15° S. One of the layers is quite fossiliferous 

and gave fine specimens of Iphideabella, Salterella conioa n. sp., Protypus 

senectus, heads of small trilobites of the genera Solenopleura and Zacanthoides, and numerous fragments of the head and thoracic segments of a 

species of Olenellus.

1 The term ''York limestone'' was proposed by Dr. Frazer for this limestone; but, as he states that 

it is a prolongation of the Lancaster limestone into York County, and that it is" more fully developed 

in Lancaster County, 1 think it best to retain the term Lancaster limestone, as it is hardly necessary 

to call the same limestone by different names in adjoining counties.

S 0n the line of strike of these beds, 2 miles northwest of Emigsville, the following fauna was 

found in the calcareous sandstones; Camarella minor, Obolella crassa (?), Hyolithes communii, and 

fragments of Olenellus.

3 Dr. Frazer's section indicates a dip of 85°. I was not able to discover the locality where it occurred.
16 CAMBRIAN BOOKS OP PENNSYLVANIA. [BULL. 134.

Section from Emigsville south through Bed Lyon Station, Pa. Cont'd. Thickness

in feet.

Farther to the westward, in an old quarry east of the Northern Central 

Kailroad track, massive layers of limestone are shown that have a strike N. 

20° W. (mag.), dip 20° 8., and contain fragments of the genera Olenellus 

and Protypus. The next higher exposure in that section is in a large, deep 

quarry just west of the railroad track, between one-fourth and one-half 

mile south of Emigsville. About 60 feet of limestone is exposed. The 

strike is E. and W. (mag.), with a dip of 10° S. In the lower portion of 

the quarry massive layers of arenaceous limestone occur, and about 10 feet 

from the summit of the section are alternating bands of earthy and pure 

limestone in which numerous fossils occur. In the collection obtained I 

have recognized plates of Cystids, Kutorgina n. sp., Billingsella festinata 

Billings, Olenellus (fragments), and Protypua senectua Billings. The fragments of Olenellus indicate individuals as large as any known. The fossils 

range through .about 20 to 25 feet of the limestone. 1 The layers above the - 

fossiliferous band are largely brecciated and form a limestone conglomerate.

In the railroad cut the limestone is shown, and a little to the north of it 

cleaved slates, the bedding of which strikes east and west (mag.), and dips 

10° S. There is an interval of 20 feet between the limestone and slates 

covered by debris. The limestone appears to pass beneath the slates, and 

from the areal distribution of the slates and limestone to the south and 

southwest it is probable that this upper band of slates has a wide distribution. Its thickness is unknown.

Estimated thickness of the entire series of limestone .................. 750

The banded limestone of No. 4 is beautifully shown in a quarry about 

one-fourth of a mile southeast of Emigsville. .This is exhibited in PI. 

Ill, where the more siliceous layers are brought out in strong relief by 

the solution of the purer limestone layers.

On the geological map of York County an area of the Hellam quartzite is indicated 2 miles northwest of Emigsville. We found this to be 

a continuation of the calcareous Olenellus quartzites beneath the limestone of the section at Emigsville. They form a narrow, continuous 

belt, and were traced northwestward nearly over to New Holland, on 

the Susquehanna.

A section from a point 1 mile east of Emigsville to the limestone 

north of New Holland shows an anticlinal structure with the Olenellus 

quartzite at the center of the anticline, and above, in turn, the shales 

and limestones. This quartzite is colored on the map as of the same 

age as the Hellam quartzite. It is, as we now know, a thinner belt of 

quartzite resting in the calcareous and sandy shales above the quartzite 

of the Hellam Hills.

The next point determined was the actual relation of the Olenellus 

quartzite at Emigsville to the massive Scolithus quartzite of the Hellam

'At a locality 4 miles north of York, on the left bank of Codorus Creek, and one-eighth of a mile 

below Meyers's mill, near Emigsville, Prof. A. Wanner and Mr. Charles Schuchert found the following 

species Eocystites , Iphidea bella Billings, two undescribed brachiopods, Billingsella feslinata 

Billings Hyolithes americanus Billings, Salterella conica n. sp., Protypus senectus Billings, Olenellus 

thompsoni Hall (?). This fauna is a characteristic middle Olenellus-zone fauna, and may be compared 

to that of the upper Winooski marble of the Vermont section. They also found, south of Eisenhardt's 

achoolhouse, on Liverpool road, 3 miles northwest of York, JBillingsella festinata Billings, Hyolithes 

americanus Billings, Salterella conican. sp., and Olenellus thompsoni Hall (?).
U. S. GEOLOGICAL SURVEY

BANDED LOWER CAMBRIAN ROCKS ONE-FOURTH MILE SOUTHWEST OF EM
WALCOTT.] YORK .COUNTY. 17

Hills. In passing from Pleasureville toward York, on the steep sidehill 2. miles west of York, there are, in the roadside, exposures of the 

shales and calcareous sandstone above the massive quartzite of the 

Hellam Hills. At a point probably 100 feet beneath the ferriferous 

shale in which the numerous ore pits occur, on the south side of the 

Hellain Hills, a species of Obolella, very closely allied to Obolella 

crassa, and fragments of Olenellus were found in the decomposed calcareous sandstone. At a locality about-1 mile south of Mount Zion 

church, in Hellam Township, and 4 miles northwest of York, numerous 

specimens of Camarella minor and fragments of Olenellus occur in a 

calcareous quartzite identical in character with that of the Emigsville 

section. These two localities prove that the Scohthus quartzites of 

the Hellam Hills and of "Chiques Bock "are beneath the Olenellus 

calcareous quartzites of the Emigsvilie section, and are therefore of 

Lower Cambrian age.

Search was next made for fossils near the base of the limestone above' 

the ferriferous shales resting on the quartzites of the Hellam Hills. They 

were found a short distance above the shales in a small quarry of thinbedded limestone by the roadside, 1 £ miles north of Stoners Station, on 

the York and Wrightsville Railway. The strike is a little north of west, 

and the dip 45° S. Finely preserved specimens of Linnarssohia, closely 

allied to Linnarssonia sagittalis, are abundant, and easily recognized 

fragments of a species of Olenellus are associated with them. Crossing 

the section to the south, occasional exposures were seen of massivebedded, light-colored limestones of much the same character as those 

exposed in the quarries north of Wrightsville, 3 miles to the eastward. 

The dip increased to 85° at the railroad track, which indicated that a 

compressed syncline had been passed over in the section.

Fine exposures of the massive and more finely bedded limestones are 

shown in the quarries in the suburbs of York. Where the soil has 

been recently removed the characteristic erosion by solution is frequently seen. This is exhibited in PI. IV, where the white limestone 

looks very much like the hummock ice of an ice floe. PI. Y is an illustration of one of the minor folds in the more finely bedded limestone. 

This is above the more massive limestones shown in Pis. IV and XL 

The massive limestones of Pis. IV and XI are correlated, although in 

PI. XI the rock is seen to carry a limestone conglomerate.

Through the efforts of Prof. A. Wanner, the fauna of the main body 

of the limestone in York County has been largely increased since my 

visit. Mr. Charles Schuchert also made a collection at Professor 

Wanner's localities. A study of all the material gives the following 

lists of species:

Fossils from Cutcamp'8 quarry, north of Cottage Hill, York, Pa. 

~ Cystidian plates. Ptychoparia adamsi Bill. 

Microdiscus, like M.parJceri Walcott. Ptychoparia teucer Bill. 

Olenellus sp. undet. Agrauloa sp. ? 

Zacanthoidea sp. ? 

Bull. 134 2
18 CAMBRIAN ROCKS OF PENNSYLVANIA. [BULL. 134.

The fauna is strongly marked by the presence of the two undetermined species of Zacanthoides and Agraulos. It is essentially of an 

upper Olenellus-zone type.

Fossils from roadside north of Highland Park, York, Pa.

Olenoides like 0. marcoui Whitfield. 

Protypus senectus Bill. 

Ptychoparia.

A fauna similar to this occurs at the upper limit of the Olenellus 

zone in the Parker section of Georgia, Vt. The absence of Olenellus 

is unusual, as that genus is almost always present in all Lower Cambrian rocks; and it may be a fair inference to consider the horizon at 

which these fossils occur as beds of passage between the Lower and 

the Middle Cambrian.

Fossils from cellar diggings, corner Penn and North streets, York, Pa.

Sponge undet. Zacanthoides sp. undet.

Eocystites. Bathyuriscus sp. undet.

Acrotreta sp. ? Ptychoparia sp. undet.

Agnostus sp. ? Ptychoparia sp. undet.

This fauna is to be referred to the lower horizon of the Middle Cambrian. It is marked by a very characteristic form of Agnostus and 

Bathyuriscus.

When examining the section on the east side of the Susquehanna, in 

Lancaster County, south of Columbia and north of Washington Manor, 

with Messrs. A. Wanner and Arthur Keith, we found a locality of 

Lower Cambrian fossils in a narrow belt of limestone about half a mile 

north of Washington Manor. In the material collected Hyolifhes cornmunis and fragments of Olenellus showing portions of the head and 

thoracic segments were recognized.

A glance at Dr. Frazer's map of York County shows tbat, in all

probability, all of the limestones, quartzites, and schists of the central 

portion of the county are of Cambrian age. The Hellam quartzite 

ridge is, as stated by Dr. Frazer, evidently an anticlinal ridge, broken 

in the northwest side by a fault that has brought the quartzites up 

against the higher horizons of the shales and limestones. The anticlinal structure apparently extends to the southwest, past York and 

toward Hanover.

The discovery of Lower Cambrian fossils in the compressed syncline 

of limestone in Lancaster County, south of Columbia, indicates that 

the limestone on the west side of the river is of the same geologic age, 

and that the shales and schists beneath it (called chlorite-schists, etc., 

by Frazer) are of Lower Cambrian age; and I doubt if there is in York 

County a sedimentary rock other than the Mesozoic New Ked sandstone of later age than the Cambrian, unless it be the Peach Bottom 

slate and chlorite-schists of the southeastern corner of the county; 

and from the closely related structure of Lancaster County it is very
U. 8. GEOLOGICAL SURVEY 

ILLUSTRATION OF EROSION BY SOLUTION BENEATH THE SOIL OF A MASSIVE BE

LIMESTONE QUARRY ON THE EAST SIDE OF YORK, PENNSYLV
WALCOTTJ SOUTH MOUNTAIN. 19

probable that all the Lancaster limestones will fall within the Cambrian, 

unless it be some portions of the npper series of limestone, which may 

pass into the Ordovician. This generalization will also apply to the 

limestones of the adjoining counties of Berks and Chester, and, in fact, 

to the entire extension of this series northeastward to the Delaware. 

All of the quartzites that have been referred to the Potsdam will necessarily fall into the Lower Cambrian, as they are beneath the limestones. 

When it is borne in mind that the quartzites that have been called 

the Potsdam by the Pennsylvania Survey are of Lower Cambrian age, 

that a series of schists and limestones suporjacent to these are of Lower 

Cambrian age, that the Potsdam horizon of the New York series is 

represented by limestones in the Auroral series of Rogers, and that 

the Calciferous-Chazy terrane of the New York section is represented 

only by the upper portion of the Auroral limestones, geologists will 

have little difficulty in determining the geologic horizons of the various 

outcrops of quartzites, schists, shales, and limestones, provided careful 

attention is paid to their sedimentary character and to the discovery 

of occasional localities of fossils.

SOUTH MOUNTAIN.

Professor Lesley states that 

The South Mountains, separating the Cumberland Valley from the lower country 

of York and Adams county, are the northernmost end of the Blue Ridge range of 

Virginia. * * * The whole measures upon the map 10 miles in breadth by 50 

in length, upon a curve extending from the Maryland line to its northeastern end, 15 

miles west of Harrisburg. 1 *

From the Pennsylvania line southwest across Maryland, South Mountain extends, as the Blue Eidge, to Harpers Ferry, and thence southwest across Yirginia. It practically includes, also, the Catoctin range, 

on the eastern side, which extends south from the southwestern portion of Adams County, Pa., and crosses the Potomac at Point of Eocks, 

and thence extends south a little west of Leesburg, Ya. The Blue Eidge 

and the Catoctin Eidge are the eastern and western sides of the mountain uplifts of which South Mountain, Pennsylvania, is the northern 

terminus. Prof. H. D. Eogers describes South Mountain as composed 

almost entirely of rocks of the " Primal series." He says:

It is doubtful if the true gneissic rocks anywhere reach the surface within its 

borders, and only in one or two localities have even the lowest members of these 

Auroral limestones been met with covering the upper Primal slates. Even of intrusive igneous rocks it embraces a singularly small amount, those met with being chiefly 

greenstone and trap rock.2

On the geologic map accompanying this report the South Mountain 

area is indicated as unaltered Primal rock. He regarded the quartzite 

of South Mountain as the Primal quartzite, and the shales as the Primal

 * Second Geol. Surv. Penn., A Summary Description of the Geology of Penn., Vol. 1,1892, p. 142» 

8 The Geology of Penn., Vol. 1,1858, p. 203.
20 CAMBRIAN ROCKS OF PENNSYLVANIA. [BULL. 134,

slates, and mentions that at one locality, Pine Grove Furnace, there 

occurs in the middle of this range of slate a narrow band of limestone, 

marking the position of the axis or keel of the trough into which the 

formations have been folded. 1 He speaks of a band of altered siliceous 

rock, and south of it a zone of green altered slate charged with epidote; 

overlying this again, another belt of a more siliceous altered slate.2 In 

speaking of the lower Primal slates beneath the quartzites, he says:

These lower Primal slates are highly indurated, and even decidedly crystalline, 

containing in some of their layers segregated specks and even half-formed geodes of 

epidote and other minerals. They bear a strong general resemblance to the half crystallized, older Primal slates just south of Spring Mill. * * * Near the tunnel at 

the northwest side of Jacks Mountain there is a hardepidote rock, and not far from 

it highly altered greenish slate a rock found in several other localities farther west, 

and containing layers of grey slate spotted.with epidote. Farther west occurs 

epidote with asbestos. 3

Of the metamorphic strata of Pennsylvania, Prof. H. D. Kogers 

. says that before the geological surveys of Pennsylvania and Virginia 

were organized the ancient and more altered strata between the summit 

of the Atlantic Slope, in the Blue Ridge and South Mountain, and its 

base at the margin -of tide water were regarded and designated alike 

as primary rocks, and were supposed to constitute but one group^the 

oldest known to geologists:

Early, however, in the course of those surveys, it came to light that by far the 

larger portion of the rocky masses of at least the middle and northwestern tracks, 

including much of the Blue Ridge and of the Green Mountains, were of a different 

type and age from the oldest metamorphic or true gneissic system. The evidence in 

support of this conclusion was, first, an obvious and very general difference in the 

composition of the two sets of strata; secondly, a marked difference in their conditions of metamorphism; and thirdly, and more especially, a striking contrast in 

the direction and manner of their uplift.'*

He regarded the sandstone with Scollihus Unearis as at the base ot 

the Paleozoic series, and believed that the Primal slates beneath the 

sandstone, and in intimate alternation with it, did not possess a vestige 

of organic life. He then states that there are now two main horizons 

subdividing the more or less metamorphic strata of the Atlantic Slope 

into three systems of groups the one, a physical break or interruption 

in the original deposition of the masses; the other, a life limit or plane 

denoting the first advent, so far as yet discovered, of organic beings. 

These two planes are not coincident, but include between them a thick 

group of sedimentary rocks, separated from the lower physically, from 

the other paleontologically. To the most ancient or lowest group he 

gave the name of the Gneissic series; to the great middle group, less 

crystalline than the gneissic, and yet destitute of fossils, the descriptive 

terms Semiinetamorphic or Azoic; and to the third or uppermost system the entire succession of the American Appalachian strata, from 

the Primal to the true coal rocks the term Paleozoic. As summed up, 

this classification is: The Hypozoic rocks, or those underneath any lifebearing strata; Azoic, or those destitute of any discovered relics of life j

'Loc. cit., p. 203. * Loc. cit., p. 205. 3 Loc. cit., p. 207. * Loc. cit., pp. 62,63.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 134 PL. V

SYNCLINAL FOLD IN THE THIN-BEDDED LOWER CAMBRIAN LIMESTONES, AS SEEN IN A QUARRY IN 

THE SUBURBS OF YORK. PENNSYLVANIA.
WALCOTT.] SOUTH MOUNTAIN. * 21

and Paleozoic, or those entombing the remains of the earth's most 

ancient forms of living beings.1

Ic is evident from Professor Eogers's definition of the Azoic group 

that it included what we now recognize as the Lower Cambrian sedimentary strata beneath the Scolithus quartzite, and also an extended 

series of altered rocks that form the nucleus of the Blue Eidge and 

which are now included in the Algonkian of the classification of the 

United States Geological Survey.

The conclusions of the geologists of the Second Geological Survey of 

Pennsylvania are that there are two groups of rocks forming South 

Mountain. Dr.' Frazer states:

Hence, it is made apparent that the great South Mountain chain is composed essentially of two groups of rocks, the lower (and along this line the northwestern) con7 

sistiag of various modifications of the quartz conglomerate above spoken of, and in 

which quartzite occurs in various forms. The upper and southeasterly group is felsitic in character, but contains also large beds of hydro-mica and chlorite schists 

intersected by veins of milk quartz, while the prthofelsite itself presents every 

variety of appearance, from a sandy and earthy slate in which the crystals of orthoclase are very much decomposed indeed are sometimes almost clay through the 

jasper-like variety to the massive and coarsely porphyritic structure in which it is 

suited to be used as an ornamental building stone. 2

In a paper entitled " The Lake Superior Copper Eocks in Pennsylvania," 3 Mr. J. F. Blandy gives a figure of an ideal section of South 

Mountain in which the sandstones pass beneath the epidote traps, etc. 

In the discussion following the reading of the paper (at a subsequent 

session) Dr. Frazer states that " the Potsdam or Primal Formation of 

Eogers is wanting all over that county, with the exception perhaps of 

detached patches on the northwest flank of the South Mountain chain." 

He reaffirms his view that the rocks of South Mountain may be divided 

into two great series: "A western (underlying), of which the characteristic strata are composed of quartzite and of arenaceous schist 

containing quartz pebbles (Mountain Creek rock), and 'the eastern 

(overlying), of hydro-mica and chlorite schists, and orthofelsite, both 

porphyritic and unporphyritic." 4 At a later date Dr. Frazer 5 explained 

the structure of the copper belt of this region by the presence of a 

series of faults, which have brought blocks of strata in different relations to one another, and thus repeated the sections:

But the great width of the South Mountain chain along the Chambersburg turnpike, the abrupt protrusion to the east of the "eastern part of the chain, south of 

the Chambersburg-Gettysburg turnpike, and of the western part of the chain to the 

west, north of this line, and the contacts of the Paleozoic and Eozoic rocks of very 

different horizons in the middle portions of the chain, all point to the existence of 

extensive longitudinal and transverse faults in these measures.

1 Geology of Pennsylvania, Vol. I, 1858, pp. 63, 64.

'Second Geol. Surv. Penn., Keportof Progress in tbe counties of York, Adams, Cumberland, and 

Franklin for 1875 (1877), p. 285.

8 Trans. Amer. Inst. Mining Eng., Vol. VII, 1879, p. 332.

«Loc. cit., p. 338.

5 An Hypothesis of the Structure of the Copper Belt of the South Mountain: Trans. Amer. Inst. 

Mining Eng., Vol. XII, 1884, pp. 82-85.
22 * CAMBRIAN BOCKS OF PENNSYLVANIA. [BULL. 134;

Professor Lesley says:

The northwestern (Mount Holly) ridge is made by several thousand feet of the 

lower quartzite and quartz conglomerate beds. The southeastern (Adams County) 

ridges are made by several thousand feet of an overlying feldspathic, micaceous, 

and chlorite series, intersected by veins of milky quartz.

These two series, or great subdivisions, seem at some places to graduate into each 

other, as if they were the earlier and later deposits of one age. In other places (as 

in the Greenwood section No. 10) they seem distinct, the passage from the lower 

quartzite series to the higher porphyritic (orthofelsite) series being abrupt, with 

even an apparent difference of strike in some of the outcrops along the line of 

section. 1

In a footnote he calls attention to the resemblance of the feldspathic 

rocks of the upper group of rocks to the kaolin slate beds in the 

Virginia Blue Ridge section at Balcony Falls, as described by Fontaine.2 

"He regards the lower, or quartzite and conglomerate slate, series as 

certainly immensely thick, and says that a total thickness of 14,000 

feet is suggested along Dr. Frazer's cross-section No. 10. Other sections 

across the mountains toward Mount Holly Springs exhibit a certain 

minimum thickness of 5,000 feet, and a possible maximum thickness 

of 10,000 feet and 12,000 feet, of quartzite series.3 It is further stated 

that the thickness of the overlying feldspathic felsite series, along the 

Mount Holly cross-section No. 8 of Dr. Frazer's, exceeds 6,000 feet, as 

shown in the broad syncline:

The Mountain Creek rock subdivision of the lower series is characterized by 

scattered pebbles and by occasional solid beds of conglomerate. Dr. Frazer gives it 

various names, descriptive of its varieties: "Schist conglomerate," "green schist 

with quartz pebbles" (some of them of transparent quartz, others of amethyst-colored 

quartz), these last two varieties of conglomerate marking a transition to the Upper 

series. It is evident that the great Lower series, if indeed it be separable from the 

Upper, has the lowest set of beds which are almost wholly of metamorphosed sand, 

quartzite; then higher sets of clay, sand, and pebble beds, metamorphosed into 

quartzose slates, shales, schists, and pebble rock.

The still higher and more or less niagnesiaii slates, hard shales, crystalline schists 

with scattered pebbles, conglomerate beds, and porphyritic beds, make an indefinite, but recognizable Upper system, in which occur also true quartzite beds, like 

those at the bottom of the Lower series. Occasional fragments of diorite trap 

appear on the surface which may indicate interbedded volcanic rocks, or possibly 

very small dikes. The whole may have been capped by the Hellam (Chiques rock) 

quartzite, fragments of which are so abundant on the lower southeast slope of the 

South Mountain mass. It is hard to avoid the inference that our South Mountain 

rocks represent the Huronian section of Murray and Logau. It is impossible not to 

compare them also with the great quartzite masses, the roofing slates, etc., of 

Walcott's Upper, Middle, and Lower Cambrian system. 4

Professor Lesley regards the conglomerate beds as fixed horizons in 

the series, and states that they may be exaggerated in number on 

account of repetition in anticlinal aud synclinal folds.5

It will be observed from the preceding views of Professor Lesley's

1 Second Geol. Surv. Penn., A Summary Description of the Geology of Penn., Vol. I, 1892, pp. 

144,145.

2 Loc. cit., p. 144. 

» Loc. cit., p. 145. 

« Loc. cit., pp. 147,148. 

 Loc. cit., p. 150.
WALCOTT.] SOUTH MOUNTAIN. 23

that he was in doubt as to. whether the South Mountain rocks were of 

Huronian or Lower Cambrian age.

In speaking of his study of the South Mountain, west of the Susquehanna and stretching southward to the Potomac, Dr. T. Sterry Hunt 

says of the pre-Paleozoic rocks:

In this portion, so far as I am aware, it shows no Laurentian north of the Potomac, 

but consists of Montalban and Huronian, the latter constituting the strata at Harpers 

Ferry and for some miles to the eastward along the Baltimore and Ohio Railroad. 

In the southern part of Pennsylvania to the west of Gettysburg this mountainous 

belt, rising between the Mesozoic on the east and the great limestone valley on the 

west, presents an immense development of a peculiar type of crystalline rocks which 

I detected there last year and which has a considerable geologic importance. It is 

a bedded petrosilex, grayish, reddish, or purple in color, sometimes granular, but 

more often jasper-like in texture, and frequently porphyritic from the presence of 

small crystals of orthoclase-feldspar or of glassy quartz. There is here found a 

great breadth of this rock Distinctly bedded, presenting different varieties, and alternating with diorite, or diabasic, epidotic,aud chloritic rocks, with argillites, in which, 

are sometimes included thin beds of petrosilex the strata generally dipping at high 

angles to the southeast. These petrosilex beds with their accompanying rocks are 

identical with those whichl have described as occurring on the eastern coast of New 

England, and farther northward along the Bay of Fundy in New Brunswick. They 

are well seen at Lyon, Saugus, and Marblehead in Massachusetts, and also on the 

shores of the Passamaquoddy Bay, where they are interstratified, as in the South 

Mountain, with rocks having the character of the Huronian series; to which great 

division I have provisionally referred these bedded petrosilex rocks, with the suggestion that they probably occupy a position near the base of the series. 1

After making the statement that the crystalline rocks of the Green 

Mountain series belong to a more ancient system, which underlies 

uncouformably the crystalline Cambrian sediments of the Quebec 

group, Dr. Hunt states that in a letter received by him from Prof. 

William B. Eogers, dated June 8, 1877, there are statements to the 

same effect in regard to similar strata in Virginia, as follows:

The sections which I had the pleasure of showing you lately, illustrating the position of the Lower Cambrian beds (our Primal conglomerate, etc.) in their contact 

with the crystalline and metamorphic rocks of the Blue Ridge in Virginia, form the 

part of a series embracing the results of some forty transverse explorations made 

during and since the Virginia geological survey at nearly equal distances across the 

chain from Harpers Ferry to the North Carolina line. In many of these sections the 

unconformity of the Cambrian upon and against crystalline and metamorphic rocks 

is unmistakable and conspicuous, the lower members of the Primal being seen to 

rest on the slope of the ridge, with northwest undulating dips, on the edges of the 

steeply southeastward-dipping older rocks. In other cases the Primal beds thrown 

into southeast dips in the hills which flank the Blue Ridge are made to underlie, 

with more or less approximation to conformity, the older rocks forming the central 

mass of the mountain. But even in these instances it is, I think, not difficult to discern the true relations of the strata. s

I)r. Hunt follows this quotation with the statement that the crystalline rocks which are the prolongation of the Blue Eidge into southern 

Pennsylvania have already been described as Huronian by him.

1 Proc. Amer. Assoc. Adv. Sci., Buffalo, N. T., 1876, published in 1877, p. 211.

2 Second Geol. Surv. Penn., Special Report on the Trap Dikes and Azoic Hocks of Southeastern 

 Pennsylvania, Part I, 1878, pp. 198, 199.
24 CAMBRIAN ROCKS OF PENNSYLVANIA. [BULL. 134.

When I began the investigation to ascertain by stratigraphic and 

paleontologic evidence the geologic age of the South Mountain quartzite and the associated schists and shales, I soon discovered that there 

was little prospect of finding the true geologic succession in the northern portion of the mountain in Cumberland and York counties, owing 

to the folding of the strata, and also to the fact that there were a number of westward thrusts of lower upon higher beds, and that, as a 

result of this, the central core of the Blue Ridge has been broken and 

thrust over on the Lower Cambrian beds, and also, in places, rests 

apparently conformably upon the latter, all having an eastward dip. 

The discovery of Olenellus with Hyoliihes communis in the massive 

quartzite series in the Mount Holly Eidge, just above Mount Holly 

Springs, in Cumberland County, proves that the great western mass of 

quartzite of South Mountain, with the interbedded shales, slates, and 

conglomerates, are of Lower Cambrian age, but it does not throw any 

light upon the geologic age of the orthofelsite series of Frazer and 

the epidote rocks of Eogers. In company with Mr. Arthur Keith, of 

the United States Geological Survey, who had mapped the Harpers 

Ferry sheet, an examination was made across the ridges from Mechanicstown, Md., to Monterey, and westward to Pikesville, in Franklin 

County, Pa. On entering the gorge a little west of Mechauicstown, on 

the line of the Western Maryland Eailroad, an extended series of 

shales and slates was passed, all having a very high dip to the southeast. About 2 miles from Mechanicstown massive quartzites were met 

having a high dip to the east, and higher up in the gorge there was 

a repetition of the slates found east of the quartzites. This section 

indicates, from the dips of the quartzites, a syncline resting on a considerable thickness of slates and shales. A series of sections, by Mr. 

Keith, of the western or Blue ridge, extending from a point 11 miles 

south of Mechanicstown to Harpers Ferry, shows that this same synclinal structure prevails all along the ridge, and that a synclinal fold 

of massive sandstone forms the summit of the ridge, below which a 

series of shales rests unconformably upon the subjacent crystalline 

rocks.1 The synclinal structure is also shown for the quartzites of 

the eastern or Catoctin ridge.

From a point 2£ miles west of Mechanicstown to Monterey the road 

led across the epidote-schists of the central nucleus of the range, which 

is now a mountain valley between the Catoctin and the Blue -ridges. 

The schists extended to a point one-fourth to one-half a mile beyond 

the Blue Eidge station, on the Western Maryland Eailroad. Fragments of a rhyolitic-like porphyritic rock were also seen, which probably represent the "bedded petrosilex" of Dr. Hunt, as shown 2 miles 

south of the Monterey road, near Foxville, Md.2 Along the road

1 The Structure of the Blue Kidgen ear Harpers Ferry: Bull. Geol. Soc., Amer., Vol. II, 1891, Pis. IV, 

andV.

JDr. George H. Williams made a detailed study of the volcanic rocks of South Mountain, in Pennsylvania and Maryland. He gives an historic sketch of the various views that prevail as to the characterf
WALCOTT.]; SOUTH MOUNTAIN. -.: 25

c beyond Pen'Mar toward Pikesville, there was an apparent repetition of the section on the eastern side of the ridge, near Mechanicstown. Subsequently an examination was made of the section from 

Monterey, Franklin County, Pa., to the valley, on the line of the 

Waynesboro turnpike. Just west of Monterey a massive quartzite 

forms a plateau, upon which the Monterey hotel is situated. The dip 

of the quartzite is slightly to the northwest. A short distance beyond 

the tollgate the dip to the northwest increases, and a series of sandy 

and argillaceous shales succeeds the quartzite. Following down the 

turnpike toward Waynesboro, and near the foot of the ridge, these 

shales were found to pass beneath a light-colored, hard, compact quartzite dipping northwest, in which numerous remains of Scolithus lineari§ 

occur. I also found, upon breaking the white quartzite, many fragments 

of Olenellus, showing parts of the head and thoracic segments. In 

calcareo-arenaceous layers, just beneath the quartzite, fragments of 

Olenellus occur associated with specimens of Gamarella minor. A series 

of more or less sandy shales next appears, resting upon the Scolithus 

quartzite and having a northwesterly dip toward the valley. Along 

the foot of the ridge low hills of shale appear, capped with thin-bedded 

calcareous quartzite or sandstone. In the latter, Gamarella minor, 

Hyolitlies communis, and fragments of Olenellus were abundant. A 

little west of the slate hills the limestones of the valley appear. In the 

limestone a little east of the road, on the East Branch of Little Antieof the rocks of South Mountain, followed by a description of the eruptives, as determined by him.

" The cause of the prevailing misconception regarding the volcanic rocks of South Mountain is not 

difficult to find. Their accompanying accumulations of tuff beds and breccias, and the fact that they 

are generally cleaved parallel to the great structure planes of the mountain, have all been readily interpreted as indications of stratification and conformity. The cleavage dip in the sandstone has often 

.been mistaken for bedding, while the thin jointing and slaty structure of the lavas, though a secondary feature, have seemed, to geologists not very familiar with recent volcanic rocks, sufficient proofs 

of sedimentary origin.

"In spite of great age and some alteration, however, the volcanic rocks of South Mountain have 

preserved all the essential characteristics of our recent rhyolites and basalts in such perfection that 

the proofs of their real nature are, to the student of comparative petrography, overwhelming, while 

to all who will candidly examine them they must be at least convincing."

In relation to the age of the South Mountain volcanics he says: " The age of the South Mountain 

volcanics and their relations to the sandstone in which Mr. Walcott has recently identified the Lower 

Cambrian fauna, are points of great" interest. The hypothesis of the Pennsylvania geologists that 

the greenstones and felsites lie above the sandstone is evidently incorrect. It may, however, be 

regarded as an open question whether the volcanic rocks represent a much older horizon, which was 

already eroded before the sandstone was deposited, 'or whether they were, in part at least, contemporaneous with the sandstones.

"The entire absence of sandstone as inclusions in the lavas, as well as in all the accumulations of 

pyroclastic material; the observations of Keith, Geiger, and Walcott, that the sandstone lies flat or 

in synclinals; and the sections made by Miss Bascom across Monterey Peak, Pine Mountain, Jack's 

Mountain, and Haycock, near Monterey, all indicate that the sandstone is altogether above the volcanic 

rocks, and that it has been only sporadically left by erosion on the east side of the mountain in Pennsylvania. In Maryland the volcanic rocks are flanked both on the east and west by sandstone. No 

alternations of relatively thin beds of sandstone and lava have thus far been observed.. The contacts 

of the sandstone above the porphyry on the old tapeworm railroad southwest of Maria's Furnace, and 

above the greenstone in the Jack's Mountain railroad tunnel are both admirable exposures, but both 

seem to be.thrust planes and are not contacts of original deposition.

"The South Mountain volcanic rocks therefore become, not merely in their petrographical character 

and richness in metallic copper, but also in their stratigraphical position, comparable with the Keewenawan or Nipigon series of Lake Superior." Am. Jour. Sci., 3d ser., Vol. XLIV, 1892, pp. 482-496.
26 CAMBRIAN BOOKS OF PENNSYLVANIA. [BULL. 134.

tarn Creek, and about 3 miles east of Waynesboro, Kutorgina n. sp. and 

fragments of the head and thoracic segments of Olenellus were found.

If reference is now made to the York County section, it will be seen 

that the upper portion of the Monterey section is essentially a repeti 

tion of it, from the Scolithus quartzite to the limestones of the valley. 

The same fossiliferous Scolithus quartzite passes beneath the shales, 

in which are interbedded calcareous quartzites carrying the Olenellus 

fauna; .these pass beneath the limestones of the valley in York County 

in which the Olenellus fauna occurs. In the Monterey section, however, there is a series of shales beneath the Scolithus quartzite, that 

rests upon a massive quartzite forming the summit of the Blue Eidge 

south of Monterey,

The Blue Eidge was followed south into Maryland and crossed at 

several points before reaching Harpers Ferry. All of the sections 

show the synclinal structure of the shales and quartzites as represented by Messrs. Geiger and Keith in their paper on the structure of 

the Blue Eidge near Harpers Ferry. 1 South of Keedysville, Washington County, Md., the quartzite capping the slate hills west of the 

main ridge was observed to pass, conformably beneath the limestone 

at Eakles Mills, and Hyolithes communis and fragments of Olenellus 

were found in the calcareous quartzite. The stratigraphic structure 

south of the Monterey section is complicated at and near Harpers 

Ferry by the massive quartzite's forming a syncline and by its being 

thrust to the westward over the more recent shales, slates, and limestones. The structure is still more obscured by the fact that the hills 

of shale (capped by the Olenellus quartzite) are thrust, on the line of a 

fault, over on limestones, which, in an unbroken section, rests upon the 

quartzites.

It was this primary folding, and subsequent westward thrusting on 

the line of two or more faults, of the older upon the more recent strata, 

at and to the north and south of Harpers Ferry, that led Messrs. 

Geiger and Keith to consider that the lower quartzites rested conformably upon the limestones and were of Silurian age. 2

Eeturning to the study of South Mountain with the information gained 

between the Potomac and the line of the Chambersburg and Gettysburg piker in Pennsylvania, and studying Dr. Frazer's sections (Nos.7, 

8,9,10,11, and 13)3 , and also reading the descriptions of them, as well 

as Professor Lesley's description of South Mountain (as contained in 

Vol. I of his final report), one sees that these investigators have misinterpreted the true geologic structure of the mountain and the relations 

of the rocks composing it. Professor Lesley states that a massive 

fault must run along the foot of the mountain, along the low drift-filled

>Bull. Geol. Soc. Amer., Vol. II, 1891, Pis. IV and V.

2 Structure of the Blue Eidge near Harpers Ferry, Va.: Bull. Geol. Soc. Amer., Vol.11, 1891, 

pp. 155-163, Pis. IV and V.

'Second Geog. Surv. Penn., Report of Progress on the Counties of York, Adams, Cumberland, and 

Franklin for 1875-1877.
WALCOCT:.] SOUTH MOUNTAIN. . ' 27

valley of Yellow Breeches Creek; aud iii this I think he is correct, asttie Olenellus fauna of the Scolithus quartzite zone occurs but a short 

distance east of the foot of the mountain in a synclinal fold, at Mount 

Holly Springs. The great error, however, is the view that the "orthofelsite" series is superior to the conglomerate, quartzites, and schists, 

which they referred to the lower. series, placing the "orthofelsite" 

series above the quartzite series. The Monterey section shows that the 

epidotic schists are inferior to the quartzites; and a section west of 

Wolfsville, Md., shows that the petrosilex or "rhyolitic-like" eruptive 

occupies a similar position. This type of section is repeated many 

times, both on the Catoctin and Blue Kidge sides, from the Maryland 

line to the Potomac, and south through Virginia.

Professor Rogers, and also Professor Lesley, referred the offsets of 

the ranges of hills of South Mountain, as shown in Franklin County, 

and also on the north end of South*Mountain, to the terminations of 

successive folds of the rocks forming the mountain. My impression is 

that these offsets, and also the complicated structure of the mountain, 

arise partly from folding, but more largely from the westward thrusts of 

masses of strata along the lines of fault of a low hade. This westward 

thrusting on the fault plane, complicated by previous folding of the 

strata, leaves masses of the subjacent, pre-Paleozoic rocks resting, in 

various places, on different members of the Lower Cambrian series, 

and also appears to interbed the quartzites and schists of the Cambrian in the schists, eruptives, etc., of the Algoukian. 1

The key to the succession of the lower sedimentary rocks of Maryland and Pennsylyama is contained in the Balcony Falls section of 

Virginia, although it can be determined by a study of the section at 

Monterey and to the south along the Blue Eidge, toward Harpers 

Ferry.

In a letter from Professor Lesley, dated February 22, 1891, he asks:

Is it possible that there should be agreement between the Balcony Falls section 

of Virginia and the Mount Holly Spring section, 300 miles apart?

He says, further, after commenting upon the possible relations 

between the Balcony Falls section and that at South Mountain, in 

speaking of the strata of the Balcony Falls section:

But what is 2,000 or 2,500 feet to 10,000 or 20,000 feet of quartzites and slates, 

making (apparently, not certainly) the South Mountains? We are still in the dark 

about super aud sub positions; about absence or presence of overturn rolls, etc. I 

am only greatly impressed with the broad fact that we seem to have the Huronian 

mass rising to view in the South Mountains of the Atlantic States.

I think that the views of Messrs. Frazer and Lesley, that such great 

thicknesses of strata occur in South Mountain, arise from the fact that

1 From the finding of the fragments of eruptive rocks in the conglomerates at the base of the quartzite 

series, and from the numerous synclines showing that the epidotic rocks and also certain rhyolitic 

eruptives are beneath the quartzite series, I refer the similar rocks of South Mountain to a pre-Paleozoic age; and, as they are not of the characters of the Laurentian crystalline complex, I would refer 

them to the Algonkian, but not correlate them with the Huronian or with any known division of that 

group of rocks. Am.'Jour. Sci., 3d ser., Vol. XLIV, 1894, p. 480.
28 CAMBRIAN ROCKS OF PENNSrLVANIA. [BULL. 134.

these "great thicknesses" are but repetitions of both the Cambrian and 

pre-Cambrian strata as a result of folding4 and overthrust faulting, and 

from failure to differentiate the cleaved schistose eruptiyes of the 

Algonkian from the bedded sedimentaries of the Lower Paleozoic.

LANCASTER, BERKS, AND LEHIGH COUNTIES.

It has been stated that Hyoliihes communis and fragments of Olenellus were recognized in the material collected from limestones in 

Lancaster County, on the east side of the Susquehanna Elver,J and 

that from the closely related stratigraphic arrangement of the rocks 

of Lancaster County it is probable that all the Lancaster limestones 

will fall within the Cambrian, unless it be that some portion of the 

upper series may pass into the Ordovician. This generalization will 

also apply to the limestone in 1Jie adjoining counties of Berks and 

Chester, and, in fact, to the entire extension of this series northeastward to the Delaware. All of the quartzites that have been referred 

to the Potsdam will necessarily fall into the Lower Cambrian, as they 

are beneath the limestones.2

Prof. A. Wanner, of York, Pa., accompanied me in the examination 

of the limestones about the city of Lancaster. His familiarity with 

the positions of the quarries and natural outcrops enabled us to make 

a rapid examination of the limestones along Conestoga Creek, and, 

although no fossils were found, I saw no reason to think that the limestones were not of Cambrian age. We next proceeded to the eastern 

side of the county, where the southern division of the limestone passes 

into Chester County. An examination was made of the lower quartzites 

and the superjacent limestones at Gap, Limeville, and toward Compassville. A few Scolithus borings were noted in the quartzites northeast of Gap, and fragments of Olenellus and specimens of Obolella 

were found in sandy layers embedded in a shale 1 mile north-northeast 

of Gap. The section from the top downward, from a point a little east 

of Gap northwest, is:

5. Massive-bedded, light-colored limestone, with partings and small, interbedded, 

flattened nodules of mica-schist.

4. Narrow belt of hydromica-schist, with thin layers of hard calcareous sandstone 

containing Obolella and fragments of Olenellus.

3. Massive beds of bluish-black and nearly white limestone, extensively quarried 

at Limeville.

2. Narrow belt of shale altered to a hydromica-schist.

1. Quartzite, in the hill northeast of Gap.

We next visited the extensive quarries at Bellemont, on the mam 

line of the Pennsylvania Railroad, 4 miles west of Gap. In the quarries the conglomerate limestone, so characteristic of the Cambrian at 

Stoners Station, in York County, are beautifully exposed, and nuiner1 Notes on the Cambrian Bocks of Pennsylvania and Maryland from the Susquehauna to the 

Potomac: Am. Jour. Sci., 3d ser., Vol. XLIV (Dec., 1892), p. 474.

2 Loc. cit., p. 475.
U. S. GEOLOGICAL SURVEY 

CLIFF OF MASSIVE-BEDDED LOWER CAMBRIAN LIMESTONES AT THE QUARRIES ON THE L

LANCASTER COUNTY, PENNSYLVAN

Bluish-black at base, white above, and capped by thinner layers of a 
WALCOTT.] NORTHERN BELT OF LIMESTONE. 29

ous photographs were taken of the conglomerate beds, showing their 

positions between the evenly bedded limestones. The limestones and 

conglomerates belong to No. 3 of the Gap section, and are overlain by a 

belt of shale in which massive beds of a fine limestone conglomerate 

occur. No time was given to searching for fossils.

PI. YI illustrates the massive-bedded limestone beneath the conglomerate limestone. This bed is very persistent, and is the source of 

most of the limestone quarried for the limekilns of this section, PI. VII 

is a view taken about one-fourth of a mile to the eastward, where the 

massive bed of limestone is capped by the conglomerate band, a thin 

bed of dark, shaly limestone intervening between them. Higher up in 

the section, about one-fourth of a mile north, the upper massive limestone is exposed in some extensive quarries. This is more siliceous 

than the beds below, and it breaks up into angular fragments, so as 

to give the appearance, when viewed at a little distance, of a cliff of 

quartzite or crystalline rock (Pl.VIII). In the immediate vicinity of the 

Bellemont quarries one of the characteristic limekilns of a generation ago 

is in a fair state of preservation. As these are rapidly passing away, a 

photograph of this kiln was taken, and it is reproduced in PI. IX.

The discovery of the Olenellus fauna in the limestone in the eastern 

portion of Lancaster County, north of Gap, taken in connection with the 

eastern section of York County, compels the reference of the so-called 

Potsdam rocks of Chester County, with their superjacent limestones, to 

the Cambrian. As mentioned previously (p. 28), it is quite probable 

that the limestones toward the Triassic area, in the northern portion 

of Lancaster County, may be of Ordovician age, but this can be proved 

only by the discovery of the fauna.

NORTHERN BELT OF LIMESTONE.

As shown by the geologic map of Pennsylvania (1884), the northern 

belt of limestone enters the State in Franklin County, and then turns 

to the northeast in Cumberland County, crosses the Susquehanna at 

Harrisburg, and extends on eastward across Dauphin, Lebanon, Berks, 

Lehigh, and Northampton counties, to the Delaware River. The Olenellus fauna was found in the quartzites of South Mountain in Adams 

County, as well as in the lower portions of the limestone in Franklin 

County.1 From this, and the fact that the lower portions of these limestones and the superjacent quartzites or sandstones were known to be 

of Lower Cambrian age in their extension into New Jersey, I began 

the examination of them in the vicinity of Beading, where their relations to the Reading sandstone are well defined. The Scolithus linearis 

occurs abundantly in the quartzites of Penn Mountain, east of Reading, and on the south side of Neversink Mountain, across the Schuylkill. In the upper layers of the sandstone or quartzite I obtained

1 Loc. cit., p. 478. , 
30 CAMBRIAN ROCKS OF PENNSYLVANIA. [BULL. 134.

Hyolitliellus micans and fragments of a species of Olenellus. This 

locality is about one-half mile above Klappenthal Station, on the 

Philadelphia and Beading Bailroad, and the terminal station of the 

electric road running out of Beading over the Neversink Mountain. 

West of the first railroad cut above the station, between the cut and 

the stone crusher, thinner beds of quartzite are met with that carry 

fossils. The quartzites are more or less contorted and folded, but their 

stratigraphic relations to the main quartzites of the mountain and to 

the adjoining limestones are readily determined. No fossils were 

observed in-the limestones.

The sections in the vicinity of Allentown and Bethlehem were examined and found to be essentially the same as at Beading, the quartzites 

passing beneath the limestone. In the quarries at Catasauqua, 4 miles 

north of Allentown, I noted the occurrence of a large Pleurotomaria, of 

the type of Pleurotomaria canadensis, of the Calciferous horizon in New 

York and Canada. In the report of the Second Pennsylvania Geological Survey of Lehigh and Northampton counties the localities of fossils 

are all represented as being on the northern side of the outcrop of 

limestone, in the strata that dip to the northward beneath the superjacent shales. The Trenton horizon is represented as in the limestone 

immediately beneath the shales (called "Hudson"); and lower down, 

in massive limestone, species of Maclurea or Eomphalus, which indicate 

the Chazy horizon, have been found.. This distribution of faunas is the 

same as in Franklin County, where the Lower Cambrian fauna occurs 

at the base of the limestone, near the quartzites, and the Trenton fauna 

at the summit, near the base of the superjacent shales.

The limestones were examined in the vicinity of Easton, along Bushkill Creek and the shores of the Delaware Biver. No fossils were found, 

with the exception of a species of Cryptozoaii; but from the similarity 

of the limestone to that of the lower portion of the series near Alientown, Beading, and in Lancaster County, it is quite probable that they 

represent the Lower Cambrian portion of the section. North of Easton 

5 or 6 miles, in the vicinity of Churchville, fossils that indicate the 

Trenton horizon were discovered by the Pennsylvania Survey. I think 

it is only a matter of detailed search and patience to discover localities 

of fossils, both in quartzites and limestones, throughout this belt, from 

where it enters the State from Maryland to where it crosses the Delaware 

into New Jersey.

If we follow the line of the strike of the limestones across the Delaware into New Jersey, the same type of section is found to extend 

northeasterly across that State and into Orange County, N. Y. At 

Hardistonville, Sussex County, N. J., Dr. Beecher discovered the 

Olenellus fauna in the blue limestones resting on the basal quartzite.1 

The fossils are found on the southeastern side of the limestone belt, 

and on the northwestern side the limestones dip beneath the shales, as

*Geol. Surv. New Jersey, Ann. Kept. State Geologist, 1890, pp. 31, 43, 49.
U. S. GEOLOGICAL SURVEY

LOWER CAMBRIAN LIMESTONE EXPOSED IN QUARRIES AT BELLEMONTE, LANCAST

PENNSYLVANIA RAILROAD, A SHORT DISTANCE 

The massive limestones are here capped by a band of limestone conglomerate that rests on th
U. S. GEOLOGICAL SURVEY 

MASblVE-BEDDtD, LIGHT-GRAY, SILICEOUS LIMESTONE, IN QUARRIES ONE-FOURT

BELLEMONTE, LANCASTER COUNTY, PE

The limestone breaks into angular fragments on the lines of th
WALCOTT.] CORRELATION. 31

in the Pennsylvania section. In the geological report of New Jersey 

for 1868, pages 131 and 132, numerous localities of the fpssiliferous 

Trenton limestone are described, and a section is given showing the 

limestone passing beneath the shales to the westward.

In the summer of 1894 I found at a point 4 miles northeast of Newfoundland, N. J., fragments of Oleuellus in the limestone resting on a 

bedded quartzite which was in contact with the pre-Cainbrian gneiss. 

The Cambrian rocks at this point are represented by a lower-quartzite 

10 or 15 feet in thickness, a massive-bedded, siliceous limestone that may 

be 200 feet thick, and a series of shales of inconsiderable thickness 

that pass beneath the Silurian (?) conglomerate of Kanouse Mountain.1

CORRELATION.

Eeference has already been made to the similarity, noted by Professor 

Lesley, between the rocks of South Mountain and those described by 

Professor Fontaine in the Balcony Falls section of Virginia. The latter 

section, as described by Mr. H. D. Campbell, in 1885, is as follows, 

from the base up:

Section at Balcony Falls, Va.

Feet.

8. Scolithus sandstone...................................................... 350

7. Slates...................................................................... 120

6. Sandstone................................................................ 90

5. Slates..................................................................... 700

4. Hard sandstone .......................................................... 150

3. Slates.................................................................... 500

2. Sandstone..............................................:................. 360

1. Conglomerate ............................................................ 120

Total................................................................. 2,390

He further states that, away from the river some distance, there are 

about 600 feet more of sandstone and friable slate before the limit of 

the Potsdam formation is reached.2

The sandstones and slates of the section, with the exception of No. 8 

(the Scolithus sandstone), and the superjacent shales, are all more or 

less feldspathic. The Scolithus sandstone and the beds just above it 

are known to be of Lower Cambrian age,3 and Cambrian fossils were 

found near the summit of the superjaceut shales beneath the limestones.

Prof. William B. Eogers traced, as he thought, the Primal sandstones and slates of the Balcony Falls section across Virginia to 

Harpers Ferry, where they crossed the Potomac and extended on 

northward along the Blue Ridge to South Mountain, southwest of the

'Am. Jour. Sci., 3d ser., Vol. XLVII, 1894, pp. 309-311.

* The Potsdam Group east of the Blue Ridge, at Balcony Falls, Va.: Am. Jour. Sci., 3d ser., Vol. 

XXIX, 1885, p. 472.

'Notes on the Cambrian Books of Virginia and the Southern Appalachians: Am. Jour. Sci., 3d ser. 

Vol. XLIV, 1892, p. 53.
32 CAMBRIAN ROCKS OF PENNSYLVANIA. [BULL. 134.

Susquehanna, in Pennsylvania. His various sections of the Blue 

Eidge show an overturn of the Primal strata to the westward, which 

gave that and the superjacent Valley limestone an easterly dip. If he 

had at that time understood the phenomena of thrust faults^! think he 

would have interpreted the structure to be a thrusting (often of a synclinal fold) of the older Primal beds over on the superjacent limestone, 

instead of an overturned anticlinal fold.

The section at Monterey, and along that portion of the Blue Eidge, 

as estimated from the data obtained by Mr. Keith to the south and 

from the Monterey section, is as follows, reading from above downward :

Section at Monterey, Va.

(The upper portion of the section is preceded by the Valley limestone, more or 

less of the lower portion of which is probably of Middle and Upper Cambrian age.)

Feet. 

6. Mottled limestone, with intercalated sandy and shaly layers. Fossils:

Kutorgina n. sp. and fragments of Olenellus..................... 800 to 1,000

5. Sandy shales, with a series of calcareous quartzite near the summit. Fossils: 

Camarella minor, Hyolithes communis, and fragments of Olenellus. About.. 450 

4. Scolithus quartzite, with interbedded calcareous sandstones and shales.

Fossils: Camarella minor and fragments of Olenellus.................... 500

3. Sandy shale, with interbedded layers of quartzite......................... 800

2. Coarse-grained and bluish-gray q uartzite......................... 1,000 to 1, 200

1. Shales and slates, well shown near Mechanicstown, Md., and in numerous

sections along the Blue Kidge...................................... 300 to 400

(At several localities the shales of No. 1 appear to be replaced by bands of conglomerate, and many of the layers of No. 2 are to a greater or less extent a conglomerate.)

The section includes from 3,000 to 3,500 feet of sandstones and shales 

before reaching the limestones. In a number of localities a conglomerate was observed in the lower sandstone series in which fragments 

of the pre-Paleozoic crystalline rocks were embedded. This phenomenon was observed on South Mountain, in the conglomerate mentioned 

by Professor Lesley, and also along the Blue Eidge and the Catoctin 

Eidge to Harpers Ferry, the conglomeritic character of the rocks 

varying very much in the character and size of the coarser material. 

The feldspathic character of these shales and sandstones is very dis- 

 tinctly marked beneath the Scolithus quartzite, in both the Balcony 

Falls and the Monterey sections. If these two sections are compared 

with that at Chickies Eock and south to Columbia, in Lancaster 

County, Pa., it will be at once observed that the Scolithus quartzite, 

while the highest band of quartzite in the Balcony Falls and the 

Monterey sections, is the lowest in the Chickies Eock section, whichhas 

the lowest feldspathic sandstone and shales apparently above the 

Scolithus quartzite. It is from this fact that it is stated, in the first 

part of this paper, that the feldspathic sandstones and shales were 

thrust over on the Scolithus sandrock in the Chickies section,
U. S. GEOLOGICAL SURVEY 

VIEW OF AN OLD LIMEKILN AT BELLEMONTE, LANCASTER COUNTY : PENNSYLVA
WALCOTT.] CORRELATION. " 33

On PI. II of Bulletin No. 81 of the United States Geological Survey, 

section 9 is intended to illustrate the Cambrian rocks of central Pennsylvania. It gives the data known at that time, but ray recent reconnaissance has disclosed the fact that a section similar to that of 

Tennessee (section 11) will more fairly represent the Cambrian rocks 

on the Susquehauna and to the southwest into Maryland.

.The discovery of the Oleuellus or Lower Cambrian fauna in the 

Beading sandstone practically completes the correlation of the South 

Mountain, Chickies, and Beading quartzites, and establishes the correctness of the early correlations of McClure, Eaton, Einmons, and Bogers. 

They all considered the basal quartzite as the same formation from 

Vermont to Tennessee; and the discoveries of recent years have proved 

that the basal sandstones of Alabama, Tennessee, and Virginia (Chilhowee quartzite); Maryland, Pennsylvania, and New Jersey (the Beading quartzite); New York and Vermont (.Bennington quartzite), were 

all deposited in Lower Cambrian time, and that they contain the characteristic Oleriellus fauna throughout their geographic distribution. 

The superjacent limestones carry the Oleuellus fauna in their lower 

portions in northern and southern Vermont, eastern New York, New 

Jersey, and Pennsylvania. To the south of Pennsylvania the lower 

portions of the limestones appear to be represented by shales, and the 

Upper and Middle Cambrian faunas are found in the lower half of the 

Knox dolomite series of Tennessee, and they will probably be discovered in the same series in Virginia and Maryland when a thorough 

search is made for them. The same may be predicted, but with less 

assurance, for the northern belt of limestone crossing Pennsylvania 

into New Jersey, as the limestones between the Olenelkis zone and the 

Trenton zone represent the intervals of the Middle and Upper Cambrian and the lower Ordovician, or the Calciferous and Chazy zones of 

the New York section. The working out of the details of this section 

in southeastern Pennsylvania is an interesting problem, left for solution to some geologist who has the necessary paleontologic training, 

and who will not be discouraged by the prospect of a good deal of 

hard work before the desired result can be obtained.

The problem of where to draw the line in this series of limestones, 

on a geologic map, between the Cambrian and Ordovician, is one that 

will seriously embarrass the geologist, but I anticipate that either lithologic or paleontologic characters will be discovered by which the two 

groups can be differentiated. If not, the limestones must be colored as 

one lithologic unit or formation, as on PI. I, and the»approximate line 

of demarcation between the Cambrian and OrdoViciau must be indicated in the columnar section accompanying the legend of the niau. 

Bull. 134 3
34 CAMBRIAN EOCKS OF PENNSYLVANIA. [BOLL. 134.

INTRAFORMATIONAL CONGLOMERATES.

In a recent article 1 I have discussed under this title a conglomerate formation, some of the principal illustrations of which occur in 

the Cambrian rocks of Pennsylvania. As this is a somewhat unusual 

phenomenon, but one that will be seen with comparative frequency in 

Pennsylvania, I here append my observations on the subject, and also 

reproduce the illustrations of the Pennsylvania localities.

DEFINITION OF TEEM AND ILLUSTRATION.

An intraforniational conglomerate is one formed within a geologic 

formation of material derived from and deposited within that formation. An illustration occurs in the old limestone quarries on the east 

shore of the Hudson, below Schodack Landing, Eensselaer County, 

N. Y. The section is formed of thinly bedded limestone carrying the 

typical Olenellus fauna. Toward the summit of the quarry a band of 

limestone conglomerate rests conformably on the bedded limestone. 

Pebbles and fragments of several varieties of limestone occur, in which 

fragments of typical species of the Oleuellus fauna were found. The 

conglomerate band varies in thickness from 2 to 6 feet, and is capped 

by thinly bedded limestones that carry the same species of fossils as 

the limestones beneath the conglomerate and the bowlders in the conglomerate. It shows that the limestone pebbles, bowlders, and brecciated fragments were formed from a calcareous sediment sufficiently 

consolidated to be broken up and more or less rounded by attrition, and 

these collected to form a bed of conglomerate, the matrix of which is 

usually calcareous. This section clearly proves the formation of conglomerate within the Lower Cambrian terrane, the materials of which 

were derived from limestones deposited during Lower Cambrian time.

The conglomerate at the locality described is not so clearly marked 

as are some in the Lower Cambrian terrane of Lancaster and York 

counties, Pa., and the conglomerates at the base of the great Ocoee 

series of Tennessee. The limestone conglomerates of the Cambrian 

and Ordovician of the St. Lawrence Valley are not typical illustrations 

of true intraformational conglomerates, but I shall speak of them, as 

they appear to have been formed under somewhat similar conditions.

CANADIAN LOCALITIES.

Sir W. E. Logan has graphically described the limestone and conglomerates of the south shore of the St. Lawrence at Trois Pistoles, 

Bic, Metis, the vicinity of Quebec, and the west coast of Newfoundland.2 During the summer of 1889 I had an opportunity to examine 

the sections of the Ordovician and Cambrian rocks in the vicinity of

1 Bull. Geol. Soc. Amer., Vol. V., 1894, pp. 191-198, Pis. V-VH. 

2 Geology of Canada, 1863, pp. 227, 260, 261,
U. S. GEOLOGICAL SURVEY 

BRECCIATED LIMESTONE CONGLOMERATE IN LOWER GRDOV1CIAN SOUTHEAST OF 
EXPOSURE OF LIMESTONE CONGLOMERATE IN LOWER CAMBRIAN LIMESTONE IN QUARRY O

CITY LIMITS.
WALCOTT.] INTRAFOKMATIONAL CONGLOMERATES. 35

Quebec, and I was very much impressed by the mode of occurrence of 

the limestone conglomerates. The lowest bed of conglomerate occurs 

in the Sillery shales on the south shore of the St. Lawrence below 

Levis and on the south shore of the island of Orleans. The limestone bowlders show transportation, and are mingled with pebbles of 

quartz, sandstone, etc. The Olenellus fauna occurs abundantly in the 

fragments of limestone, but the source of the limestone is unknown. 

It is, however, of Cambrian age, and it has been redeposited about 

1,500 feet from the summit of the series of shales, sandstones, etc., 

that are referred to the Cambrian.1

The lower bed of limestone conglomerate at Point Levis occurs near 

the base of the Ordovician, in the Point Levis shale. It is made up of 

large and small bowlders of limestone, carrying the Upper Cambrian 

fauna, that are embedded in the limestone matrix in which occurs the 

typical Calciferous fauna. The matrix is a hard, gray, impure limestone, 

which forms solid layers that were traced for over 500 feet on the strike. 

As in the case of the limestone bowlders carrying the Oleuellus fauna, 

the origin of the bowlders carrying the Upper Cambrian fauna is 

unknown, as no beds of limestone of a similar character have been 

found in the Sillery shales, upon which the Ordovician shales and interbedded conglomerate rest. The matrix of the conglomerate proves the 

formation to be of lower Ordovician age. In a bed of limestone 50 feet 

higher up in the section I found additional species of the Calciferous 

fauna, and in a bed of limestone conglomerate above this the fossils in 

the bowlders, and in the matrix as well, are of Calciferous age. In a 

search of two days I failed to find a Cambrian fossil at this horizon, 

although such a discovery might be anticipated from the occurrence 

of the older limestones in the conglomerates beneath. This second 

band of conglomerate in the Levis series appears to be true iutraformational conglomerate. The limestone conglomerates embedded in 

the shales and shaly limestones beneath the city of Quebec are of much 

less stratigraphic importance than are those at Point Levis; but the 

same conditions of deposition appear to have existed during the formation of these rocks of middle Ordovician (Chazy-Trenton) time.

VERMONT AND NEW YORK LOCALITIES.

In the passage beds between the Cambrian and Ordovician east of 

Highgate Springs, Franklin County, Vt., layers of limestone conglomerate occur (PI. X), some of the fragments of which carry the lower 

Ordovician fauna. The horizon of the conglomerate appears to be 

within the range of this fauna, and points to an iutraformational origin.

The type that has already been described as .occurring at Schodack 

Landing, N. Y., has been observed at many localities to the north, in 

Washington County, N. Y., where it is a common feature of the Lower 

Cambrian terrane.

i Am. Jour. Sci., 3d ser., Vol. XXXIX, 1890, pp. 112-113.
36 CAMBEIAN BOCKS OF PENNSYLVANIA. [BULL. 134. 

PENNSYLVANIA LOCALITIES. 1

The succession of 'Cambrian rocks in York and Lancaster counties, 

Pa., is very clearly defined. A massive quartzite is succeeded by 

shales, and then comes a massive-bedded, more or less siliceous limestone that varies in color and composition in its several beds. This 

massive bed of limestone is succeeded in numerous instances by beds 

of limestone conglomerate, which are interbedded in more or less thinly 

bedded, somewhat shaly limestones. One of the most clearly defined 

sections is exposed at Bellemont, Lancaster County., on the line of the 

Pennsylvania Railroad. The massive blue and white Cambrian limestones are succeeded by a few feet of a blue, earthy limestone and 

shale, and upon this there is a bed of limestone conglomerate, from 8 

to 10 feet in thickness, that is made up largely of pebbles and bowlders of limestone derived from the limestone beds beneath. (PI. VII.) 

A second bed of conglomerate is seen on the roadside to the north.

About 40 miles west of Bellemout, at Stoners Station, on the York 

and Wrightsville Eailroad, York County, Pa., an extensive and beautiful exposure of the Lower Cambrian limestones and conglomerate may 

be seen in an old quarry just east of the wagon road, one-fourth of a 

mile north of the railroad track. (PI. XII.) Alternating bands of 

thinly bedded limestone and massive beds of limestone conglomerate 

form about 100 feet of the exposed section, in which five beds of the? 

conglomerate limestone are well shown. The basal bed has a finegrained, gray limestone matrix with brecciated limestone fragments in 

it, which range in size from that of small shot to masses 3 feet in 

diameter. These pebbles and bowlders vary in lithologic character, 

some resembling the matrix and others being oolitic, arenaceous, seraimarbleized, and shaly limestones. The thinly bedded limestones separating the conglomerate bands are from 4 to 6 feet in thickness, and 

are very clearly defined.

In the second band of conglomerate the larger bowlders occur in the 

lower portion. The other three beds vary in details, but they are all 

formed of the same type of rock. One of the upper beds contains a 

multitude of small fragments of limestone. It was impracticable to 

obtain a photograph of the basal beds, which contain the largest 

bowlders. PI. XII illustrates the evenly bedded limestones above and 

beneath the third band, and also shows the character of some of the 

limestone bowlders. In the shaly limestone at the base of this bed a 

larger bowlder, 2 feet or more in diameter, is entirely embedded in the 

shaly limestone. This bowlder, as shown in Pis. XIII and XIV, was 

evidently deposited on the bed of the sea, and the calcareous mud

'Mr. Frederick Prime, jr., noted the brecciated conglomerates jn the limestone of Lehigh and Northampton counties, Pa. They occur between bauds of unbroken limestone, and he explained the phenomenon by the fractxire of unyielding beds between two more pliable ones and receinenting in situ by 

the percolation of calcareous waters. (On the Paleozoic Kocke of Lehigh and, Northampton counties, 

Pa.; Amen Phjjpg, §90., Proc., VpJ. XVII, 1878, p. 250.)
U. R. GEOLOGICAL SURVEY 

LIMESTONE CONGLOMERATE AT QUARRY ONE-FOURTH MILE NORTH OF STONERS STAT

PENNSYLVANIA,
U S. GEOLOGICAL SURVF 

VIEW OF A BOWLDER IN THE THIN-BEDDED LIMESTONE BETWEEN THE BEDS OF LIMESTON

NORTH OF STONERS STATION, YORK AND WRIGHTSVILLE RAILROAD, Y
WALCOTT.] INTRAFORMATIONAL CONGLOMERATES. 37

gathered quietly about it. At about the same horizon, in a quarry on 

the east side of York, a massive bed of limestone conglomerate is 

beautifully shown. A photograph .of it is reproduced as PL XI.

The quartzites, shales, and limestones beneath these beds of conglomerate are known to carry the Lower Cambrian or Olenellus fauna; 

and the same fauna, with the exception of details of variation of 

species, occurs in the limestones and shales above the conglomerates, 

thus placing the latter within the definition of intraformational conglomerates.

VIRGINIA LOCALITIES.

Mr. M. E. Campbell' informs me that in the vicinity of Radford, Va., 

there is a formation that appears to be a true intraformational conglomerate. He states that it is in the great Cambro-Silurian limestone, 

and consists of a yellowish-white, chalky limestone matrix iu which 

are embedded rounded fragments of limestone that are similar in composition to the matrix, and that can be distinguished from it only with 

difficulty. A few small grains of foreign material were observed. The 

exact stratigraphic horizon could not be determined, owing to the complexity of the structure and the poor exposures. Two miles below 

Eadford the actual contact was observed between the conglomerate 

and the bedded limestone, where the former rests on the cut edges of 

tbe folded limestones beneath. Mr. Campbell believes this indicates 

shore conditions, contortion of the limestone deposits, and their elevation above sea-level to form cliffs that supplied material for later beds 

of the same great formation.

Another case of this kind was observed by Mr. Campbell at a horizon northwest of Bristol, Ya. He found that here the conglomerate 

occurs in a bed of shaly limestone, only a few feet thick, that belongs in 

the Nolichucky (Cambrian) shales. This bed appears to have been 

broken up largely into flat fragments that were quite well worn on 

their edges, and then redeposited in the same bed and cemented into a 

solid mass of limestone. The peculiar features of this deposit are its 

extreme thinness and apparent freedom from all marks of erosion." It 

is quite persistent, and no evidence of an unconformity was observed.

TENNESSEE -LOCALITIES.

The intraformational conglomerates already described have been 

identified as such by the presence of similar fossils in the bowlders of 

the conglomerate and the super]acent and subjacent bedded limestones. 

Those about to be described are identified entirely by lithologic characters. These, however, are so clearly defined and are of such variety 

that the conclusions based upon them are considered to be nearly as 

reliable as those where fossils are present.

In Tennessee these conglomerates occur in the lower portion of the 

Ocoee terrane of Safford. Mr. Arthur Keith named the basal slate the

'Paleozoic Overlaps in Montgomery and Pulaski Counties, A7 a.: Bull. Geol. Soc. of Am., \Tol. V, 

pp. 175-176.
38 CAMBRIAN ROCKS OF PENNSYLVANIA. [BULL. 134.

Wilhite. This slate rarely exceeds 700 feet in thickness, and it is 

capped by the siliceous Citico conglomerate (Keith). Within the Wilhite slate, especially in the upper 200 feet, and along its strike for over 

100 miles, numerous beds of limestone occur. Usually a limestone conglomerate is found in the same section, generally above the bedded 

limestone. These limestone conglomerates have been cited as proof 

that the Wilhite slates were of later age than the Ordovician limestones, 

which, it Avas assumed, furnished the pebbles and bowlders of the limestone conglomerates; and hence, it was concluded, the Ocoee terrane, 

instead of being an older formation than the great limestone series of 

Tennessee, is of later date, and consequently of post-Ordovician age.

In company with Mr. Keith I visited numerous^localities of the Wilhite slate in Cocke, Sevier, and Blount counties. At a locality 3 miles 

S., 65° E. of East Fork, Sevier County, a limestone conglomerate occurs 

by the roadside, and also on the north side of the road, on Stephen 

Huff's farm. The bedded limestones vary in texture and color and in 

the presence or absence of more or less arenaceous material, but the 

weathered surfaces of many of the beds are very characteristic. At 

the locality by the roadside there is little, if any, of the bedded 

limestone exposed, the conglomerates resting on calcareous shale or 

slate containing compressed lentils of impure bituminous limestone. 

The conglomerate is formed of brecciated and rounded pebbles and 

bowlders of limestone and, more rarely, of a fine-grained sandstone. 

The limestone bowlders vary in lithologic characters from pure white 

limestone to sandy and siliceous and their various combinations. In 

color they are blue, gray, black, purple, white, pinkish, dove, etc. 

About 2 miles to the north of this locality, on Wilhite Creek, there 

occurs a somewhat similar conglomerate, in which the limestone bowlders reach a diameter, of from. 3 to 4 feet. A peculiarity of the conglomerate at these places is the presence of large bowlders in the 

slate above the main body of the conglomerate.

At a locality 2 miles east of Jones Cove, Sevier County, an interesting phase of the conglomerate is the presence of bowlders of a dark, 

sandy limestone embedded in the mass of the bedded limestone that 

occurs below and also above the conglomerate. The matrix of the conglomerate is frequently largely made up of a sandy limestone of the 

same lithologic aspect as the bedded limestones out of which the bowlders of the conglomerate were made. The limestone conglomerate was 

also noted at a locality 3 miles south of Del Eio, Cocke County, where 

it occurs above the limestone in the Wilhite slate.

One of the best localities,at which to study the relations of the limestones and conglomerates is on the north side of the entrance to the 

narrows of the Little Tennessee Eiver, in Blount County. Here the 

bedded limestones in the Wilhite slates are beautifully exhibited, and 

above them the limestone conglomerate is strongly marked, and bowlders of the limestone over 6 feet in diameter occur in the lower portion 

of the Citico conglomerate. Another peculiarity at this locality is that
U, S. GEOLOGICAL SURVEY 

NEARER VIEW OF THE BOWLDER SHOWN IN PLATE Xlll, SEEN F
WALCOTT,] INTRAFORMATIONAL CONGLOMERATES. 39

the limestones within the Wilhite slate were broken up and many of 

the fragments rounded to form a bed of conglomerate just above the 

horizon of the limestone beds from which, elsewhere, they were derived, 

and the same process was repeated with the bed of conglomerate. We 

found in an upper bed of conglomerate bowlders formed of masses of 

conglomerate of the same character as that in the stratum some distance below in the section. In this upper conglomerate numerous 

quartz pebbles of the same character as those of the Citico conglomerate are embedded in the limestone matrix. Special effort was made, 

by both Mr. Keith and. myself, to discover evidence of the presence of 

limestones of a character different from that of those found conformably 

bedded in the Wilhite slate, but without success. The limestones of 

the Wilhite slates are so marked in their lithologic characters, a'ud the 

bowlders in the conglomerates have lithologic characters so similar, 

that we did not hesitate to refer the source of the material of the latter 

conglomerate to the limestone beds within the Wilhite formation. At 

one locality, 2 miles S., 10° W. of Sweetwater, Cocke County, a sandstone rests unconformably upon the Knox limestone and contains 

rounded pebbles of the limestone carrying the characteristic fossils 

which are embedded in the limestone O beneath the sandstone. This 

sandstone occurs in the isolated outcrop and is not known to be of

Ocoee age.

ORIGIN.

The relation of the bedded limestone to the superjacent conglomerates proves that the calcareous mud which was subsequently consolidated into the limestones solidified soon after deposition. This is 

shown by the presence in the conglomerate of rounded pebbles and 

angular fragments of limestone with sharp, clear-cut edges. The presence of the conglomerates above the limestone beds, from some portion 

of which they were derived, leads me to believe that the sea bed was 

raised in ridges or domes above the sea-level and thus subjected to the 

action of the seashore ice, if present, and the aerial agents of erosion. 

From the fact that the limestones upon which the conglomerates rest 

rarely, if ever, show traces of erosion where the conglomerates come 

into contact with them, the inference is drawn that the d6bris worn 

from the ridges was deposited in the intervening depressions beneath 

the sea. In the case of the conglomerates of the Wilhite slates of 

Tennessee, it is exceptional to find a bedded limestone above them; 

but within the Lower Cambrian of Pennsylvania and New York the 

conglomerates are iuterbedded in the limestones.

Large bowlders of limestone were observed in the Wilhite slates on 

Wilhite Creek, Tennessee, above the main conglomerate bed, and large 

bowlders of limestone were observed in the bedded limestones at Stouer's quarry, Pennsylvania. The mode of occurrence of these bowlders, 

especially those in the limestones at Stoner's quarry, leads to the view 

that they may have been dropped upon the sea bed from, floating ice. 

No other explanation occurs to me that will account for the transpor-
40 CAMBRIAN ROCKS OF PENNSYLVANIA. [BULL. 134.

tation of a bowlder from the shore-line and the placing of it upon the 

sea bed so as not to disturb to any marked degree the sediment then 

accumulating. In the special example at Stoner's quarry 2 feet of calcareous mud was deposited in thin layers about the bowlder, and as 

much more above it, before the introduction of conditions that led to 

the deposition of the next stratum of conglomerate. 1

The history of Appalachian sedimentation and mountain-building 

proyes that a more or less constant movement was taking place from 

Algonkian time to the close of the Paleozoic.2 This movement was at 

times greatly prolonged, and resulted in marked topographic features. 

More frequently the minor movements produced local effects, and some 

of them resulted in the formation of the conglomerates described.

MODE OF FORMATION OF THIN-BEDDED BRECCIAS.

The mode of formation of a brecciatecl limestone conglomerate, illustrated by PI. X, has often puzzled me when studying Paleozoic rocks. 

Geologists frequently observe layers composed almost entirely of thinbedded, brecciated limestones, or of sandy or argillaceous shales. In 

many cases the layers of breccia are not more than an inch or two in 

thickness and occur between layers formed of undisturbed sediment. 

The breccia is often composed0 of angular fragments varying from a 

quarter of an inch to half an inch in thickness, while in the thicker 

layers of the breccia fragments an inch or more in thickness occur.

During the summer of 1895, when making observations on the flats 

exposed at.low tide in the inlet west of Noyes Point, Rhode Island, 

I noticed that when the tide went out before daylight the layer of 

fine sand and mud exposed to the dry wind and sun during the day 

hardened, and that when the surface of the water of the incoming tide 

was broken by small waves the hardened layer was lifted, broken into 

angular fragments, and piled in some places to a depth of several 

inches, while, in other places it was simply turned over and was very 

little disturbed. When much disturbed the edges of the fragments 

were rounded, so as to give them the appearance of having been rolled 

a considerable distance. In one instance the ensuing outflowing tide 

deposited a thin layer of sand and silt over the brecciated fragments. 

From these observations it is evident that should the same phenomena 

occur oh a sinking shore-line, breccias of the character so often met 

with by the field geologist would be formed.

On PI. XV parts of two photographs taken by me on the occasion 

referred to illustrate a portion of the breccia formed on the flat in the 

inlet west of Noyes Point.

'Sir William Dawson says that the " only means of explaining these conglomerates [Quebec, Point 

Levis, Me'tis] seems to he the action of coast ice, -which at this period appears to have been as energetic on the American shores as at the present day, and seems to have had great reefs o£ limestone, 

probably in the area of the Gulf of St. Lawrence, to act upon and to remove in large slabs and bowlders, piling these up on banks, to constitute masses of conglomerate." (Quart. Jour. Geol. Soc. London, Vol. XLIV, November, 1888, pp. 809, 810.)

2 See articles by Willis, Thirteenth Annual Eeport of IT. S. Geol. Surv., 1893, Pt, II, pp 217-274, 

and by Keith, Proc. Philos. Soc. Washington, 1892, Vol. XII, pp. 71-88, PI. I.
U. S. GEOLOGICAL SURVEY 

BRECCIATEO LAYER OF FINE SAND AND SILT PRODUCED BY THE INFLOWING TIDE BREAKING 

FLAT IN INLET WEST OF NOYES POINT, RHOD
INDEX.

Page. 

Acrotreta sp. ? ............................. 18

Agnostussp. 1.............................. 18

Agraulos sp. ? from near York, Pa.......... 17

Anticline, absence of any, in the New Bed

sandstone of York County......... 15

Auroral limestone and its equivalent...... 11,12

Azoic rocks of Rogers ..................... 20,21

Azoic slates of Frazer ..................... 11

Balcony Falls section of Virginia........... 31

the key to succession of lowers edimentary rocks of Maryland and Pennsylvania. .............................. 27

Bathyuriscus sp. undet .................... 18

Beecher, Dr., discovery by, in New Jersey, 

of Oleuellus fauna in blue limestone 

resting on basal quartzite.......... 30

Berks County, Cambrian rooks in.......... 28

Billingsella festinata Billings, found near

York, Pa........................... 10

iu JEmigsville section................... 16

Black Ri ver-Chazy limestone, equivalent of,

in Pennsylvania.................... 11

Blandy, J. F., paper by, on "The Lake Superior Copper Rocks in Pennsylvania, "reference to................ 21

Blue Ridge, relation of the, to South Mountain ................................ 19

synclinal structure of the.............. 24

Breccias, thin-bedded, mode of formation of 40 

Calciferous limestones of New York, equivalent of, in Lancaster County...... 12

Calciferous sand-rock of New York, equivalent of, in Pennsyl vania .......... 11

Caiuarella minor ..................... 15,17, 25, 32

Cambrian age, formations iu central portion of York County of............ 18

reference of the Potsdam rocks and limestones of Chester County to the.... 29

Cambrian system in Pennsylvania, representation of the.................... 10

Cambrian, strata in Pennsylvania referred

to the, prior to 1892................. 9

Cambrian rocks, succession of, in York and

Lancaster counties................. 36

Catoctin range, relation of the, to South

Mountain.......................... 19

Chickies quartzite at Chickies Rock, description of........................ 13

description of, by Frazer............... 13

Chiques Rock section, a study of the...... 14

remarks o» the, by Lesley ............. 13

Page- 

" Cinques" sandstone, description of, by

Lesley............................. 12

Chlorite-schists of York County........... 11

Conglomerates, iutral'ormaUonal........... 34-40

Correlation................................. 31-33

Cryptozoan, finding of a species of, in limestone near Easton.................. 30

Crystalline schists of York County........ L2

Cystidian plates from near York, Pa....... 17

in Emigsvillo section .................. 16

.1 migsville section, description of, by

Frazer ............................. 14

examination of the..................... 14

south through Red Lyon Station....... 15-16

Eocystites .................................. 16,18

Fossils from York and vicinity............ 17,18

Frazer, Persifor, jr., description of the

Emigsville section by.............. 14

description of the He!lam ("Chikis")

qiiartzite by........................ 12

quoted on the rocks composing the

South Mountain chain............. 2]

subdivision of formations in York

County by.......................... H

Gap, Lancaster County, section near....... 28

Geology of South Mountains, Lesley's

opinion upon the ................... 11

Gneissic series of Rogers .................. 20

Hellam Hills, formations in the............ 13

Hellam quartzito of York, description of,

by Frazer .......................... 12

Hellam quartzite ridge, anticlinal character

of the.............. ................ 18

Hunt, T. Sterry, views of, regarding formations of South Mountain........... 23

Hydromica-schists of York County........ 11

reference of, by Frazer................. 10

Hyolithes americauus Billings, found near

York, Pa........................... 16

Hyolithes communis.............. 15,18,25, 26,28

found in massive quartzite series...... 24

 in Monterey section.................... 32

Hyolithellus micans ........................ 30

Hypozoic rocks of Rogers.................. 20

Intraformational conglomerates ........... 34-40

Canadian localities of............... 34-35,40

definition of term, and illustration..... 34

mode of formation of thin-bedded breccias ................................ 40

origin of............................... 39-40

Pennsylvania localities of',,,.,......... 88-37
42 INDEX.

Intraformatioual conglomerates, Tennessee

localities of ........................ 37-39

Vermont and New York localities of. - - 35 

Virginia localities of................... 37

Iphidea bella Billings...................... 15

found near York, Pa ................... 16

Keith, Arthur, assistance rendered by...... 18,

24, 38, 39 

Kutorgina n. sp. ill Emigs ville section...... 36

in Monterey section.................... 32

Lancaster, Berks, and Lehigh counties,

Cambrian rocks in ................. 28-29

Lancaster limestones, and their equivalent. 12 

in York County........................ 15

reference of, to the Cambrian........... 19

report on, by Frazer.................... 12

Lehigh County, Cambrian rocks in......... 28

Lesley, J. P., classification of purple shale.8

of South Mountain by.............. 10-11

description and classification of rocks

of South Mountain by ............. 22

description of the "Chiques" sandstone by............................ 12

summary of the Primal Quartzite formation by.......................... 9

views of, regarding the relations of the 

Balcony Falls and South Mountain 

sections............................ 27

Limestone, Auroral, and its equivalent..... 11-12

Calciferous, of New York, equivalent of,

in Lancaster County................ 12

northern belt of........................ 29-31

(Silurio-Cambrian?),of YorkCounty... 11 

Trenton, equivalent of, in Lancaster

County............................. 12

Linnarssonia sagittalis..................... 17

Mesozoic "New lied" sandstones of Frazer. 11 

Mctamorphic strata, of Pennsylvania,

Rogers's views concerning the..... 20

of the Alantic Slope, division of the, by

Kogers............................. 20

Monterey section........................... 32

a repetition of York County section.... 26

Microdiscus, like M. parkeri Walcott, from

near York, Pa...................... 17

"New Red" sandstones (Mesozoic) , of

Frazer ............................. 11

Northern belt of limestone................. 29-31

Obolella crassa(?).......................... 15-17

Olenellus or Lower Cambrian fauna, discovery of, in Lancaster County........ 29

discovery of, in New Jersey, in blue

limestones resting on basal quar tzite 30 

discovery of, in quartzites of Adams 

County, and in limestone of Franklin 

County............................. 29

discovery of, in Heading sandstone, importance of the..................... 33

in Emigsville section................... 15-16

Olenellus quartzite at Emigsville, relation 

of, to the Scolithus quartzite of 

Hellam Hills....................... 16-17

Olenellus sp. undet., from near York, Pa.... 17

Olenellus thompsoni Hall, found near York,

Pa ................................. 16

Page. 

Olenoides, like 0. marcoui "Whitfield........ 18

Ordovician, possible passage into the, of the

upper series of Lancaster limestones 19 

probable representation of the, in Lancaster County...................... 29

Paleozoic series of Rogers.................. 20,21

Parker section of Georgia, Vt., fauna of the. 18 

Pleurotomaria canadensis.................. 30

Potsdam rocks of Chester County, reference

of the, to the Cambrian............. 29

Primalnewerslate, description of, by Rogers 10 

Primal quartzite, as described by Frederick

Prime, jr........................... 10

correlation of........................... 10

of Rogers, extent of, in Pennsylvania.. 9 

of Rogers, inclusion of, in Cambrian system ................................ 9

thickness of............................ 10

'' Primal sandstone " (Potsdam)............ 11

tracing of, by Rogers, across Virginia

and the Potomao to South Mountain. 19-20 

Primal slates, developmentandextentof the 10 " 

Protypus, fragments of, in Emigsville section ................................ 16

Protypus senectus Billings................. 15,18

found near York, Pa.................... 16

in Emigsville section................... 16

Ptychoparia................................ 18

Ptychoparia adamsi Billings, from near

York, Pa........................... 17

Ptychoparia sp. undet...................... 18

Ptychoparia teucer Billings, from near

York, Pa........................... 17

Quartzite, Lower, geologic age of the...... 11

Olenellus, at Emigsville, relation of, to 

the Scolithus quartzite of Hellam 

Hills............................... 16,17

(Potsdam ?) of York County ........... 11

Primal, of Rogers, extent of, in Pennsylvania. ........................... 9

Scolithus, of the Hellam Hills, relation 

of, to the Olenellus quartzito at 

EmigsviUe......................... 16-17

Red Lyon Station, section through......... 15-16

Rogers, H. D., description of highest Primal

newer slate by ..................... 10

Primal Quartzite of, included in Cambrian system....................... 9

quoted on the rocks of South Mountain.. 19-20 

reference of a series of slates to Primal

period by........................... 10

Salterella comica n. sp...................... . 15

found near York, Pa................... 16

Sandstones, "New Red," of Frazer, Mesozoic ................................ 11

Scolithus linearis ....................... 20,25,29

Scolithus quartzite. at " Chiques Rock " ... 13 

in Monterey section.................... 32

Lower Cambrian age of the............ 17

Scolithus sandstone in Balcony Falls section ................................ 31

Schuchert, Charles, collections in York

County by.......................... 16,17

Section at Balcony Falls, Va............... 31

at Monterey, Va........................ 32
INDEX. 43

Section from Emigsville south through Red

Lyon Station,Pa................... 15-16

Sections by Arthur Keith of the Blue

Ridge, reference to................. 24

Semimetamorphic or A zoic series of Rogers. 20 

Slates, Azoic, of Frazer .................... 11

beneath the Lancaster limestone, stratigraphic position of................. 13

Primal, development and extent of upper part of......... '...... .......... 10

Primal newer, description of. by Rogers. 10 

referred by Rogers to Primal period.... 10

Solenopleura............................... 15

South Mountain, Cambrian rocks of........ 19-28

Hunt's views regarding the formations

of.................................. 23

misinterpretation of the geologic structure of............................. 26-27

purple shales-of, classification of, by

Lesley ............................. 10.11

South Mountain chain, rocks composing the 21 

South Mountain quartzite, difficulty of findthe true geologic age of the........ 24

South Mountain rocks, description and

classification of, by Lesley ......... 22

Page.

South Mountain rocks, reference of, by

Lesley, to the Cambrian ........... 9

views regarding the character of the... 24-25

Sponge undet.............................. 18

Structure of the Blue Ridge............... 24

Synclinal structure along the Blue Ridge... 24

Trenton limestones of New York, equivalent of, in Lancaster County........ 12

"Upper Primal slate formation " of Rogers,

correctness of...................... 13

Valley limestone above the Monterey section, age of the..................... 32

Wanner, A., assistance rendered by..... 13,17,18 

collections in York County by......... 16,17

Williams, George H., views of, regarding

the rocks of South Mountain....... 24-25

York County, Cambrian rocks of........... ] 1-19

York County formations, Frazer's subdivision of........................... 11

York County section, Monterey section a

repetition of the................... 26

"York shales," a name proposed for shales

atHellam Hills .................... 14

Zacanthoides............................ 15,17,18