The Shenango Formation 

(Mississippian) in 

Northwestern Pennsylvania

By GRANT E. KIMMEL and GEORGE R. SCHINER

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1294-C

Prepared in cooperation with the 

Pennsylvania Topographic and 

Geologic Survey
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

U.S. GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1970

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.G. 20402 - Price 15 cents (paper cover)
CONTENTS

Page

Abstract. ______________ ___________________________________________ Cl

Introduction._____________________________________________________ 1

Previous investigations-____________________________________________ 3

Shenango Formation.______________________________________________ 4

Lower member.___-____--_-__--_-_-___-__-______-__-_---_--_-_ 8

Upper member._______________________________________________ 8

M easured sections._ _______________________________________________ 9

References_ _____________________________________________________ 13

ILLUSTRATIONS

Page

FIGURE 1. Map of northwestern Pennsjrlvania, showing principal geographic features, names of counties and quadrangles mentioned in report, and location of area shown in figure 2____- C2

2. Generalized geologic map of parts of the Shenango and Stoneboro quadrangles, Mercer County, Pa., showing location of 

sections and wells, and township names mentioned in report- _ 4

3. Chart showing stratigraphic names applied to some of the Mississippian rocks in northwestern Pennsylvania-____________ 5

4. Geologic sections and gamma-ray logs showing the lithologic 

variation of the lower member of the Shenango Formation, 

and the relation of the upper member to the lower member 

and the Pottsville Group in the Shenango and Stoneboro 

quadrangles, Pennsylvania-___-______----_------_------- 6

CONTRIBUTIONS TO STRATIGRAPHY

THE SHENANGO FORMATION (MISSISSIPPIAN) IN 

NORTHWESTERN PENNSYLVANIA

By GRANT E. KIMMEL and GEORGE R. SCHINER

ABSTRACT

The top two units of Mississippian rocks are herein defined as upper and 

lower members of the Shenango Formation. The upper member is mostly shale, 

and the lower member is principally sandstone and subordinate interbedded 

shales. A type section is established for the Shenango Formation which is about 

150 feet thick in the Shenango River valley. Measured sections and gamma-ray 

logs of wells show that the individual sandstones of the lower member of the 

Shenango Formation are not mappable units. The upper member of the Shenango 

Formation has been correlated by previous workers with the Hempfield Shale, 

but detailed geologic mapping by the authors indicates that the name Hempfield 

Shale was applied to a nonmappable shale within the Shenango Formation. The 

Hempfield Shale is herein abandoned.

INTRODUCTION

The Shenango Formation and the overlying Hempfield Shale of 

Mississippian age have been mapped and correlated widely over 

northwestern Pennsylvania without benefit of established type sections. 

Rapid lateral and vertical lithologic changes in these rocks have led to 

some confusion in their mapping, and have created nomenclatural and 

correlation problems involving the two rock units. Detailed geologic 

mapping of the Mississippian section in the Shenango and Stoneboro quadrangles (fig. 1) has resulted in better definition of the 

Shenango Formation.

The purpose of this report is to establish a type section for the 

Shenango Formation, divide it into two members, show its lithologic 

variability, clarify the stratigraphic relationship between the Shenango Formation and the various units called Hempfield Shale, and 

abandon the name Hempfield Shale.

Cl
C2

43'

CONTRIBUTIONS TO STRATIGRAPHY

81° 80°

42'

41

40°

r i V '

^-^ /

,^0 \ ! ,^ :* A -X v/ X j ^ [--^ ^X^ ' ^--

- 1 i i > Q PITTSBURGH

i .,^! *M I

Wheeling fefl

.XN

25 

I

50 MILES

FIGUBE 1. Map of northwestern Pennsylvania, showing principal geographic 

features, names of counties and quadrangles mentioned in report, and location of area shown in figure 2 (stippled area).
SHENANGO FORMATION, NORTHWESTERN PENNSYLVANIA C3

The upper and lower members of the Shenango Formation crop out 

in a wide belt in Warren, Crawford, Venango, and Mercer Counties, 

Pa., and in eastern Ohio (fig. 1). They comprise the two upper units 

of the Mississippian rocks in northwestern Pennsylvania. The lower 

member of the Shenango Formation overlies the Meadville Shale of 

the Cuyahoga Group (Gushing and others, 1931, p. 48-54), and 

represents a distinct change in the sedimentation of the Appalachian 

basin. The Cuyahoga Group consists mainly of shale and siltstone 

with subordinate variable-sized lenses and large discontinuous sheetlike bodies of flaggy very fine grained sandstone. The lower member 

of the Shenango Formation, on the other hand, is principally sandstone. It is commonly coarser grained than the sandstone of the 

Cuyahoga and contains subordinate interbeddecl shales. The basal 

sandstone of the lowTer member is usually separated from the underlying Meadville Shale of the Cuyahoga Group by a distinct erosional 

contact.

Beds of shale and siltstone and scattered lenses of fine-grained 

sandstone of the upper member of the Shenango Formation overlie 

the lower member and grade into it. In northwestern Pennsylvania, the 

topmost Mississippian shales are unconformably overlain by the Pottsville Group of Pennsylvania!! age. A geologic map of the upper and 

lower members of the Shenango Formation in parts of the Shenango 

and Stoneboro 15-minute quadrangles is shown in figure 2.

PREVIOUS INVESTIGATIONS

The stratigraphic nomenclature for the Mississippian rocks in northwestern Pennsylvania was first introduced by I. C. White in reports of 

reconnaissance investigations in Mercer (1880) and Crawford (1881) 

Counties. White named a 3- to 35-foot-thick sandstone and about 45 

feet of overlying shale exposed in the Shenango River valley the 

Shenango Sandstone and the Shenango Shale, respectively (White, 

1880, p. 59). Caster (1934, p. 138-142) agreed with White regarding 

the separation of these rock units, but changed the name of White's 

Shenango Shale to Hempfield Shale to avoid using the same geographic 

name for more than one formation.

Reports on the geology of the Oil City quadrangle (Dickey and 

others, 1943), the Mercer quadrangle (Poth, 1963), and the Neshannock quadrangle (Carswell and Bennett, 1963) used the name Shenango Formation for a much thicker, more complex unit than White's 

Shenango Sandstone. Dickey and others (1943, p. 15-18) divided the 

formation into three units of sandstone and two units of shale. They 

correlated the shale overlying the Shenango Formation with the Patton Formation. Carswell and Bennett (1963, p. 22) mapped the She-
C4

80°25'

CONTRIBUTIONS TO STRATIGRAPHY

20' 80" 15'

EXPLANATION

U) <

11

Cuyahoga Group 

and older rocks

Approximate contact

3190

Location and number of well in 

which gammaray logs were 

made

Location of

rock section

TSis type section;

RS is reference

section

FIGURE 2. Generalized geologic map of parts of the Shenango and Stoneboro 

quadrangles, Mercer County, Pa., showing location of sections and wells, and 

township names mentioned in report. For location of area see figure 1. Geologic 

sections and gamma-ray logs are shown in figure 4.

nango Formation as a unit that increased in thickness from 10 feet in 

the northwestern part of the Neshamiock quadrangle to 80 feet in the 

southeastern part of the quadrangle. They mapped the shale overlying 

the Shenango as the Hempfield Shale. Figure 3 shows how the stratigraphic nomenclature pertient to this report was applied by the various 

workers.

SHENANGO FORMATION

White (1880, p. 163) described a section about 2 miles north of Big 

Bend, Mercer County, Pa., but he did not designate a type section of 

the Shenango Sandstone, Although the top of the formation is covered 

at this locality, it is one of the best exposures of the Shenango Forma-
SHENANGO FORMATION, NORTHWESTERN PENNSYLVANIA C5

White 

(1880,1881)

Caster 

(1934)

Dickey, Sherrill,

and Matteson

(1943)

Carswell and 

Bennett 

(1963)

Poth 

(1963)

This 

report

Patton 

Formation

Hempfield 

Shale

Shenango 

Shale

Hempfield 

Shale

Shenango 

Formation

Shenango 

Formation

Shenango 

Formation

Shenango 

Sandstone

Shenango 

Sandstone

Upper 

member

Lower 

member

Meadville 

Shale

Meadville 

Monothem

Cuyahoga 

Group

Meadville 

Shale

Cuyahoga 

Group

FIGURE 3. Stratigraphic names applied to some of the Mississippian rocks in 

northwestern Pennsylvania.

tion iii the Shenango River valley. The authors propose to name this 

exposure the type section of the Shenango Formation and here divide 

it into upper and lower members. A description of the top part of the 

lower member of the formation, which was not exposed at the type section, was prepared from a reference section 8 miles north of the type 

section. The lateral variations in the formation are clearly illustrated 

by the gamma-ray logs of three wells shown in figure -i, along with a 

graphic description of the sections.

At least part of the problem in the correlation of White's Shenango 

Sandstone with the Shenango Formation of later workers (specifically 

in the area to the east and south of the Shenango River valley and generally in Mercer and Crawford Counties) is clue to White's interpretation of the rocks overlying the bottom sandstone at the type section. 

White correlated the top sandstone of the lower member of the Shenango Formation of this report with the Sharon Conglomerate of 

White (1880, p. 163), a basal sandstone of the Pottsville Group of 

Pennsylvania!! age. This top sandstone is similar lithologically to the 

bottom sandstone of the Shenango Formation and is overlain by shale 

containing worm borings and fucoids of the same type that occur 

throughout the Mississippian section of this region. Thus, the sandstone is undoubtedly Mississippian in age. A study of the section and 

other sections made by White in Mercer and Crawford Counties re362-656 O 70 2
C6 CONTRIBUTIONS TO STRATIGRAPHY

EXPLANATION

TYPE Wen

SECTION 2516

Section 1 Gamma-ray intensity increases -

Concealed

White's Shenango Shale 

Caster's Hempfield Shale

Meadville Shale 

(Cuyahoga Group)

FIGURE 4. Lithologic variation of the lower member of the Shenango Formation, 

Group in the Shenango and Stoneboro quadrangles, Pennsylvania. Locaveals that lie believed the Shenango to consist of a single sandstone 

unit not more than about 35 feet thick overlying- the Meadville Shale. 

White's Shenango Sandstone is, therefore, correlative in most places 

to the basal sandstone unit of the much thicker Shenango Formation 

as defined in this report.

White designated the shale overlying the basal sandstone of the 

type section as the Shenango shale; however, the correlations in figure 

4 show that it is only the first shale unit above the basal sandstone of
SHENANGO FORMATION, NORTHWESTERN PENNSYLVANIA C7

Well 

3190

REFERENCE 

SECTION 

Section 2

NOTE: The locations of sections and logs 

are shown on geologic map in 

text. Datum plane is the base 

of Shenango Formation. Logging 

is from top down.

Upper member 

Shenango Formation

Lower member

henango Formation

Meadville Shale

(Cuyahoga Group)

and the relation of the upper member to the lower member and the Pottsville 

tions of the geologic sections and gamma-ray logs are shown in figure 2.

the Shenango Formation. This shale becomes sandy eastward and is 

not a mappable unit. Further confusion exists because Caster (1934) 

renamed the Shenango Shale the Hempfield Shale and designated the 

type locality as Hempfield Township, Mercer County, Pa. (fig. 2). He 

did not locate a type section but stated that the Hempfield Shale was 

well exposed there. Geologic mapping in Hempfield Towmship by the 

present authors shows that these exposed shales underlie the Shenango 

Formation and are part of the Cuyahoga Group. The Shenango For-
C8 CONTRIBUTIONS TO STRATIGRAPHY

mation underlies the uplands in Hempfield Township, but only the 

basal sandstone of the formation crops out to any great degree. The 

upper member of the Shenango Formation is not exposed, owing to the 

cover of glacial drift, and therefore could not be the well-exposed shale 

referred to by Caster as the Hempfield.

Because the name Hempfield \vas applied to shales that are not 

considered mappable by the present authors and that are included in 

the lower member of the Shenango Formation as defined in this report, 

the name Hempfield Shale is herein abandoned.

LOWER MEMBER

Detailed mapping by the present authors shows that the lower 

member of the Shenango Formation in Mercer and Crawford Counties 

consists of several beds of fine- to medium-grained sandstone. Some 

beds are as much as 50 feet thick and have flaggy to blocky partings 

(McKee and Weir, 1953). Low-angle crossbedding is present locally. 

Shale and siltstone occur between the sandstone beds, and in some localities may comprise as much as one-half of the formation. The siltstones contain brachiopods, pelecypods, worm borings and trails, and 

fucoids; ripple marks are present locally. The measured thickness of 

the formation, where not eroded, ranges from about 80 feet to 120 feet 

in the Shenango and Stoneboro quadrangles.

The type section consists mainly of a basal sandstone 14 feet thick; 

an interval of shale, containing sandstone lenses, 34 feet thick; and a 

top sandstone at least 24 feet but not more than 39 feet thick. The same 

sandstone units are present in the gamma-ray log of well 2516, but part 

of the top sandstone unit is replaced by beds of shale. The logs of wells 

3190 and 3184 show that east and northeast of the type section prominent'sandstones are present in the same interval that includes shale at 

the type section. The reference section contains about 5 feet of mediumgrained crossbedded slabby sandstone in the middle part of the lower 

member, but the sandstones of the section do not correlate completely 

with the log of well 3184. Logs of wells west and south of those shown 

in figure 4 indicate that the member grades laterally into sandstone 

beds of various thicknesses, -and individual sandstones are difficult (if 

not impossible) to correlate over the distance of a quadrangle.

UPPER MEMBER

Beds of shale and siltstone containing lenses of siltstone and finegrained sandstone overlie the lower member of the Shenango Formation and grade into it. These beds are similar to parts of the lower
SHENANGO FORMATION, NORTHWESTERN PENNSYLVANIA C9

member and can only be distinguished from it where sufficient section 

is present to recognize the top of the lower member. Worm borings, 

fucoids, and current-striation marks are present on some of the siltstones. Partial exposures of these beds are described in the measured 

sections at the end of this report. The maximum thickness of these 

beds, in the area mapped, is 78 feet at the type section for the Shenango 

Formation described in section 1; however, the thickness may be 

greater elsewhere, as the exposures 'are poor in the area. Where overlain by sandstone of the Connoquenessing Formation (Pennsylvanian) of the Pottsville Group, the beds comprise a unit that is readily 

identified in geophysical logs and that can be traced across the Stoneboro quadrangle and into the adjacent quadrangles. Where the unit 

is overlain by shale of the Connoquenessing, the formation boundary 

in the subsurface is arbitrary. (See well 3190 in fig. 4.)

The unit is separated from the Pennsylvania!! rocks by an unconformity which cuts across successively younger formations to the 

southeast. At the Allegheny Front all of the Mississippian section may 

be exposed. Somewhere between the Stoneboro quadrangle and the 

Allegheny Front, the relation of the upper member of the Shenango 

Formation and the Mississippian rocks overlying the units could be 

established.

Dickey and others (1943, p. 14) correlated these rocks with shale 

of the Patton Formation in west-central Pennsylvania; however, this 

formation is poorly defined, and its stratigraphic position is not clearly 

understood. The authors do not believe that this correlation is accurate. 

The name Hempfield was applied to the upper member of the Shenango Formation of this report by Poth (1963) in the Mercer quadrangle, and by Carswell and Bennett (1963) in the southeast part of 

the Neshannock quadrangle; however, because the name Hempfield 

was given to rocks identified as part of the Guyahoga Group by Caster 

and to units within the lower member of the Shenango Formation of 

White, the present authors do not recognize Hempfield as a valid 

formation.

MEASURED SECTIONS

The sections were measured with an altimeter, hand level, and tape. 

Kock-color names are those given in the "Rock-Color Chart" of the 

Geological Society of America (Goddard, and others, 1963).
CIO CONTRIBUTIONS TO STRATIGRAPHY

Section 1

[Type section of the Shenango Formation along an unnamed stream on the east side of 

the Shenango River valley, Delaware Township, Mercer County, Pa. Base of section is 

at lat. 41°18'36" N., long. 80°18'52" E. 'Section extends 0.5 mile upstream from the 

base]

Pennsylvanian System. 

Pottsville Group.

Connoquenessing Formation:

Sandstone, white to very light gray, fine- to coarse-grained, 

blocky to flaggy___________________________ 22.0

Total thickness of exposed Connoquenessing Formation _ 22. 0

Mississippian System. 

Shenango Formation. 

Upper member:

Covered _________________________________ 7. 0 

Sandstone, light-olive-gray, very fine-grained, silty, flaggy; 

greenish-gray siltstone and shale; worm borings, worm 

trails, and fucoid marks in siltstone __ 5. 0 

Shale, dark-brownish-gray to medium-gray; tabular; silty

concretions _______________ _ _______ _ 6.0 

Sandstone, light-gray, very fine-grained to fine-grained, platy 

to flaggy; mostly planar bedded; crossbedded in part; 

finely broken plant material on some parting surfaces 6. 0 

Covered _______________________________ 10. 0 

Sandstone, medium-light-gray, very fine grained, micaceous,

platy to flaggy 1.0 

Limestone, brownish-gray, silty _ . 7 

Shale, brownish-gray; lenses of medium-light-gray very fine

grained sandstone _____ _ 12.0 

Siltstone, medium-gray, sandy, well-indurated, shaly; planar 

top with current striations and groove casts; irregular bottom; concretions at base ____________ _ _ 1.6 

Shale, medium-dark-gray to brownish-gray, fissile __ 4.0 

Covered _________________________________ 6.0 

Shale, medium-dark-gray, silty, micaceous 1. 0 

Covered; has a few shale outcrops_______________ 7.0 

Shale, dark-greenish-gray, silty, micaceous; a few thin sandstones and siltstones__________ 11. 0

Total thickness of exposed upper member_________ 78. 3

Lower member:

Covered; probably made up mostly of lower member 15. 0 

Sandstone, very light gray, fine-grained; flaggy at top; slabby 

at bottom ; parting surfaces generally irregular; some crossbedding ________________________________ 11.0 

Standstone, very light gray, fine-grained, blocky; clay galls 

and cavities at bottom; about 1 foot of erosional relief at 

base ________________________________ 13.0
SHENANGO FORMATION, NORTHWESTERN PENNSYLVANIA Cll

Section 1 Continued 

Mississippian System Continued 

Shenango Formation Continued

Lower member Continued Th(jeet) 8S 

Sandstone, medium-light-gray, very fine grained, silty, micaceous, platy, flaggy; crossbedded and planar bedded; finely 

broken plant material on some parting surfaces_ _ 4. 2 

Shale, olive-gray to medium-dark-gray, fissile; concretions;

few platy siltstones_________________________ 3.7 

Shale, medium-dark-gray; lenses of very fine grained platy,

planar-bedded, micaceous medium-gray siltstone______ 27. 3 

Sandstone, medium-light-gray, very fine grained, micaceous, 

platy, planar-bedded ; scattered crinoid-stem and brachiopod 

fragments; finely broken plant material__________ 2. 0 

Sandstone, medium-light-gray to light-gray, fine-grained, platy 

to flaggy ; olay galls at base ; about 1.5 feet of erosional relief 

at contact with underlying unit_________________ 12. 0

Total thickness of exposed lower member_________ 73. 2

Total thickness of exposed Shenango Formation___ 151.5

Meadville Shale:

Shale, medium-dark-gray, fissile; lenses of silty fine-grained

sandstone containing shale interbeds___ _ _ 4. 9 

Sandstone, light-olive-gray, fine-grained, flaggy; lenselike

crossbeds ____________ _____ 2.6

Total thickness of exposed Meadville Shale___ 7. 5

Section 2

[Reference section along an unnamed stream on north valley wall of Little Shenango 

River 4.5 miles northeast of Greenville, Pa., in Salem Township, Mercer County. Base 

of section is at lat. 41°25'40" N., long. S0°17'15" E. Section extends 0.5 mile upstream 

from the base]

Pennsylvanian System. 

Pottsville Group:

Sandstone; weathers yellowish orange to very pale orange; white 

on leached surfaces ; fine grained at top to medium grained near 

base; few pebbles; thin bedded to laminated; crossbedded_ 15.0 

Shale, dark-gray, silty, micaceous, fissile; contains organic 

material _________________________________ 18. 7

Total thickness of exposed Pottsville Group _ 33.7
C12 CONTRIBUTIONS TO STRATIGRAPHY

Section 2 Continued 

Mississippian System.

Shenango Formation. 

Upper member:

Sandstone, medium-dark-gray, very fine grained, silty, micaceous, flaggy to platy; top flags have rough surfaces and 

worm bores; some planar flag's have current-striation 

marks _________________________________ 5. 0 

Covered ____________________________ __ 15.0 

Sandstone, medium-light-gray, silty, hard, micaceous; laminated planar-bedded slab, 0.4 to 0.7 foot thick, underlain by 

shale _______________________________ 1.0 

Covered _________________________________ 9. 0 

Shale, dark-gray; very thin interbeds of micaceous mediumgray siltstone containing casts of current striations; brachiopods; unit capped by 0.9 foot laminated, hard sandy siltstone _________________________________ 12.0 

Covered _________________________________ 6. 0 

Shale, dark-gray, fissile; concretions; lenses of flaggy to 

platy siltstone and interbedded shale as much as 3 feet 

thick; current-striation casts; brachiopods__ _ 15. 0

Total thickness of upper member______ _ 63. 0

Lower member:

Sandstone, light-gray, very fine grained to fine-grained; 

flaggy irregular parting surfaces; worm borings 7.0

Shale, dark-gray, fissile; persistent break in sandstone____ . 3

Sandstone, medium-light-gray, very fine grained, silty, micaceous, platy; a few thin shale partings; 0.2 foot discontinuous calcareous sandstone near base_____________ 7. 0

Shale, dark-gray, fissile; interbeds of shale and flaggy laminated siltstone; some ripple-marked siltstones _ 11.6

Covered _________________________________ 6. 0

Sandstone, light-gray, fine- to medium-grained, blocky to 

flaggy ; crossbedded in part____________ _ 5. 0

Shale, medium-dark-gray, silty, micaceous; interbeds of 

flaggy siltstone; worm borings_____ _ 14.8

Sandstone, light-gray, fine- to medium-grained; flaggy

irregular surfaces_________________________ 3. 3

Covered _________________________________ 10.0

Sandstone, light-gray, fine- to medium-grained; flaggy irregular surfaces_____________________________ 5. 5

Shale, dark-gray, fissile; lenses of platy, micaceous very fine 

grained sandstone________________________ 2. 7
SHENANGO FORMATION, NORTHWESTERN PENNSYLVANIA C13

Section 2 Continued 

Mississippian System Continued 

Shenango Formation Continued

Lower member Continued Thickness

Sandstone, light-gray, fine-grained; flaggy irregular surfaces; 

top 1 foot platy, micaceous very fine grained; about 0.5 

foot of erosional relief at contact with underlying unit 13. 0

Total thickness of lower member_ 86. 2

Total thickness of Shenango Formation 149. 2

Meadville Shale:

Shale, dark-gray; shaly, sandy, siltstone_ 3.5

Total thickness of exposed Meadville Shale 3. 5

REFERENCES

Carswell, L. D., and Bennett, G. D., 1963, Geology and hydrology of the Neshannock quadrangle, Mercer and Lawrence Counties, Pennsylvania: Pennsylvania Geol. Survey, 4th ser., Bull. W-15,90 p.

Caster, K. E., 1934, The stratigraphy and paleontology of northwestern Pennsylvania ; Part 1, Stratigraphy: Am. Paleontology Bull., v. 21, no. 71, 185 p.

Gushing, H. P., Leverett, Frank, and Van Horn, F. R., 1931, Geology and mineral 

resources of the Cleveland district, Ohio: U.S. Geol. Survey Bull. 818, 138 p.

Dickey, P. A., Sherrill, R. E., and Matteson, L. S., 1943, Oil and gas geology of 

the Oil City quadrangle, Pennsylvania: Pennsylvania Geol. Survey, 4th ser., 

Bull. M-25,195 p.

Goddard, E. N., Chm., and others, 1963, Rock-color chart: Geol. Soc. of America.

McKee, E. D., and Weir, G. W., 1953, Terminology for stratification and crossstratification in sediments: Geol. Soc. America Bull., v. 64, no. 4, p. 381-390.

Poth, C. W., 1963, Geology and hydrology of the Mercer quadrangle, Mercer, 

Lawrence, and Butler Counties, Pennsylvania: Pennsylvania Geol. Survey, 

4th ser., Bull. W-16,149 p.

White, I. C., 1880, The geology of Mercer County: Pennsylvania Geol. Survey, 2d, 

Rept. QQQ, 233 p.

 1881, The geology of Erie and Orawford Counties: Pennsylvania Geol. 

Survey, 2d, Rept. QQQQ, 406 p.

o