Tbe Shawangunk Formation 

(Upper Ordovician(?) to 

Middle Silurian) in 

Eastern Pennsylvania 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 744 


Work done in cooperation with the Pennsylvania 

Department of Environmental Resources, 

Bureau of 1opographic and Geological Survey 

The Shawangunk Formation 

CUpper Ordovician(?) to 

Middle Silurian) in 

Eastern Pennsylvania 

By JACK B. EPSTEIN and ANITA G. EPSTEIN 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 744 


Work done in cooperation 7.vith the Pennsylvania 

Department of Environmental Resources, 

Bureau of 1opographic and Geological Survey 

Statigraphy, petrography, sedimentology, and a 

discussion of the age of a lower Paleozoic fluvial 

and transitional marine clastic sequence in 

eastern Pennsylvania 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1972 

UNITED STATES DEPARTMENT OF THE INTERIOR 


ROGERS C. B. MORTON, Secretary 


GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 74-189667 

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


Washington, D.C. 20402 - Price 65 cents (paper cover) 


Stock Number 2401-2098 

CONTENTS 

Page 

Abstract 	 1 

1 Introduction ------------------------------------------------------------­

Shavvangunk Formation --------------------------------------------------­ 1 

Weiders Member -----------------------------------------------------­ 2 

Minsi Member -------------------------------------------------------­ 5 

Lizard Creek Member ------------------------------------------------­ 7 

Tammany Member --------------------------------------------------­ 12 

Age of the Shavvangunk Formation -------------------------------------- 14 

Depositional environments and paleogeography -----------------------------­ 16 

Measured sections -------------------------------------------------------­ 23 

References cited ---------------------------------------------------------­ 42 

ILLUSTRATIONS 

Page 

FIGURE 1. Generalized geologic map shovving outcrop belt of the Shavvangunk Formation in eastern 

Pennsylvania and northvvestern Nevv Jersey ---------------------------------- 3 

2. Stratigraphic section of the Shavvangunk Formation in the report area -------------- 3 

3-21. Photographs shovving3. Conglomerate and quartzite, Weiders Member, Lehigh Gap ---------------- 4 

4. Photomicrograph of lithic grayvvacke, basal Weiders Member, Lehigh Gap -- 4 

5. Quartzite and conglomerate, Minsi Member, Delavvare Water Gap __________ 5 

6. Conglomeratic quartzite and quartzite, Minsi Member, Delavvare Water Gap__ 5 

7. Photomicrograph of feldspathic sandstone, Minsi Member, Delavvare Water Gap 6 

8. Mud cracks in siltstone, Minsi Member, Delavvare Water Gap ---------------- 6 

9. Siltstone, shale, and quartzite, Lizard Creek Member, Lehigh Gap __________ 7 

10. 	 Laminated vvell-sorted calcitic sandstone, Lizard Creek Member, Delavvare Water 

Gap ---------------------------------------------------------------- 8 

11. 	 Flaser-bedded and lenticular sandstone and siltstone, Lizard Creek Member, 

Delavvare Water Gap ------------------------------------------------ 8 

12. Soft-rock convolutions, Lizard Creek Member, Delavvare Water Gap ________ 9 

13. Rippled sandstone, Lizard Creek Member, Delavvare Water Gap ____________ 9 

14. 	 Photomicrograph of fine-grained quartzite, Lizard Creek Member, Delavvare 

Water Gap --------------------------------------------------------- 9 

15. Burrovvs in siltstone, Lizard Creek Member, Delavvare Water Gap __________ 10 

16. Burrovv in laminated red siltstone, Lizard Creek Member, Lehigh Gap ______ 11 

17. Photomicrograph of hematitic orthoquartzite, Lizard Creek Member, Lehigh Gap 11 

18. Nodule beds in Lizard Creek Member, Lehigh Gap ------------------------ 12 

19. Shavvangunk Formation at Delavvare Water Gap __________________________ 13 

20. 	 Photomicrograph of conglomeratic coarse-grained protoquartzite, Tammany 

Member, Delavvare Water Gap --------------------------------------- 14 

21. 	 Dolomite and dolomitic shale or shaly dolomite, Tammany Member, Delavvare 

Water Gap ---------------------------------------------------------- 14 

m 
IV CONTENTS 

Page 

FIGURE 22. Block diagram showing sedimentary environments and major lithofacies in the 

Shawangunk Formation ---------------------------------------------------- 17 

23. Histograms showing current trends from crossbedding ------------------------=----- 18 

24. Photograph showing tidal-flat flaser bedding in Lizard Creek Member, Lehigh Gap ____ 19 

TABLE 

TABLE 1. Chemical and semiquantitative spectrographic analyses of rocks in the Shawangunk 

Formation ------------------------------------------------------------------ 2 
THE SHAWANGUNK FORMATION (UPPER ORDOVICIAN(?) TO MIDDLE SILURIAN) 


IN EASTERN PENNSYLVANIA 


By JACK B. EPSTEIN and ANITA G. EPSTEIN 

ABSTRACT 

The Shawangunk Formation of Early and Middle Silurian 

age, and possibly Late Ordovician age, in eastern Pennsylvania and northwestern New Jersey forms a thick clastic 

wedge of sediments derived from sourcelands to the southeast 

uplifted during the Taconic orogeny. The formation is divided 

into four newly defined members, from bottom to top: Weiders 

Member (coarse conglomerate and quartzose sandstone), 

Minsi Member (quartzose conglomeratic sandstone and minor 

argillite), Lizard Creek Member (complex sequence of 

quartzose sandstone, siltstone, shale, and a few red beds, with 

sparse fauna), and Tammany Member (quartzose conglomeratic sandstone and minor argillite). The Weiders Member 

pinches out to the east near Smith Gap. The Tammany Member cannot be conveniently mapped west of Smith Gap because 

of interfingering with and replacement by beds of the Lizard 

Creek Member. The contact of the Shawangunk with the 

underlying Martinsburg Formation is an angular unconformity. The boundary between the Shawangunk and overlying 

Bloomsburg Red Beds is irregular and transitional through 

about 130-700 feet of red, green, and gray rocks. Sedimentary 

features in the Shawangunk indicate that the sediments were 

deposited by streams and in a complex transitional marinecontinental environment, including tidal flats, barrier bars, 

estuaries, and lagoons. 

INTRODUCTION 

The Shawangunk Formation of Early and Middle 

Silurian, and possibly Late Ordovician, age has been 

mapped for 40 miles between Delaware Water Gap, 

N.J., and Bake Oven Knob, Pa. (fig. 1). It forms a 

prominent ridge known as Kittatinny Mountain in 

the northeastern part of the area and as Blue Mountain in the southwestern part. The Shawangunk is 

folded, and in many places the rocks are overturned 

to the southeast. The structure is more complex in 

the southwest part of the report area; there the 

Shawangunk is faulted and in places doubly overturned to the northwest. Several wind and water 

gaps transect the ridge; the formation is well exposed only in these gaps. Between gaps, good exposures are generally lacking, but some lithologic 

information can be obtained by tracing float; thicknesses can be determined by constructing cross sections. Figure 2 shows a stratigraphic section of the 

Shawangunk compiled from sections measured at 

Delaware Water Gap, Wind Gap, Lehigh Gap, and 

Bake Oven Knob and from mapping between sections. Maps. of some areas are already publishedPortland quadrangle (Drake and others, 1969) and 

Stroudsburg quadrangle (Epstein, 1971, 1972). 

Some details from other quadrangles are given in 

Epstein and Epstein (1967, 1969). Table 1 gives 

chemical and semiquantitative spectrographic analyses of rocks in the Shawangunk Formation. 

The Shawangunk Formation consists predominantly of quartzose sandstone (quartzite), quartz-, 

chert-, shale-, and quartzite-pebble conglomerate, 

siltstone, and shale, as well as a few beds of sandstone and siltstone containing nodules of collophane, 

siderite, and chlorite. Red beds are not uncommon 

in the western part of the report area, and dolomite 

occurs at Delaware Water Gap. Fossils are rare. 

Four distinct lithic assemblages have been mapped. 

These are herein defined as members and include, 

in general ascending order, the W eiders, Minsi, Lizard Creek, and Tammany Members (fig. 2). 

We wish to thank Gary E. Redline for assisting in 

measurem,ent of stratigraphic sections. Wallace 

deWitt, Jr., U.S. Geological Survey, and W. D. Sevon 

and D. M. Hoskins, Pennsylvania Geological Survey, 

made many helpful suggestions on the original 

manuscript. SHAWANGUNK FORMATION 

The Shawangunk Grit was named by Mather 

( 1840) for sandstones and conglomerates in southeastern New York that are part of the same outcrop 

belt as rocks in eastern Pennsylvania called Levant 

by Rogers (1858) and Oneida and Medina by White 

(1882). Grabau (1909) first used the term Shawangunk Conglomerate for these rocks in eastern Pennsylvania. The lithic modifier was changed from conglomerate to formation in the Delaware Water Gap 

area by Drake, Epstein, and Aaron ( 1969). A history 

of the early nomenclature is given by Schuchert 

(1916) and Swartz and Swartz (1931). 

Swartz and Swartz (1931) traced the Tuscarora 

Sandstone and Clinton Formation from central Pennsylvania eastward to Delaware Water Gap; there, 

1 
2 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

TABLE !.-Chemical and semiquantitative spectrographic 

analyses of rocks from the Shawangunk Formation 

[Rapid-rock analyses by P. Elmore, G. Chloe, J. Kelsey, S. Botts, H. Smith, J. Glenn, and L. Artis, U.S. Geological Survey. Semiquantitative spectrographic analyses by J. L. Harris, U.S. Geological Survey. N, not detected or at limit of detection ; L, detected but below limit of determination The following elements were looked for and not detected or were found i~ amounts at the limit of detection: As, Au, Bi, Cd, Eu, Ge, Hf, In, Li, 

Nd, Pd, Pr, Pt, Re, Sb, Sm, Sn, Te, Th, Tl, U, W. The following ele­ ments were not looked for in samples 1-5 and were looked for but not detected in sample 6: Dy, Er, Gd, Ho, Lu, Tb, Tm] 

2 3 4 5 

Chemical analysis 

[Weight percent] 

Si02 -------­ 76.6 67.3 92.2 72.3 82.9 67.7 Al20a ------­ 11.0 18.3 2.5 12.3 5.3 4.8 Fe20a ------­ .68 1.6 1.0 5.3 2.2 6.6 FeO --------­ 2.2 .76 1.1 1.3 3.5 2.5 MgO -------- CaO --------­ 1.7 

.24 1.2 

.32 .37 

.13 1.0 .14 1.1 .81 1.0 5.5 Na20 -------­ .03 .18 .00 .00 .12 .02 K20 --------­ 3.2 5.7 .26 3.5 .98 1.3 H20­ ------­ .24 .38 .09 .29 .11 .65 H20+ ------­ 2.3 2.5 1.2 2.5 1.6 2.2 Ti02 -------­ • 75 1.1 .28 1.1 .45 .43 P20s -------­ .11 .04 .00 .06 .27 4.1 MnO -------­ .04 .02 .04 .03 .02 .81 C02 --------­ <.05 .10 <.05 <.05 .05 1. 7 

Total -------9-9-.1---9-9.-5---99-.2---9-9-.8---99-.-4---9-9-.3 

Spectrographic analysis 

[Parts per million] 

Ag ---------- N N N N N 5 

B ----------- 70 100 L 50 30 L Ba __________ 500 500 50 200 150 200 

Be ---------- 2 5 N 1 N 2 

Co ---------- 7 7 N 15 15 15 

Cr ---------- 50 70 5 70 30 50 Cu ---------- 30 15 10 3 7 50 La ---------- 70 100 N 70 70 50 

Mo ---------- N N N N N 5 20 7 20 7 7 ~f ~~~~~~~~~ :g L L 30 30 L 

Ph ---------- N N N 2 N 3 Sr ----------- 10 30 3 50 10 200 v ----------- 70 100 20 70 30 50 y ----------- 15 50 10 50 20 100 Zr ----------200 500 100 700 700 500 Ce __________300 500 200 500 500 500 Ga ---------- 7 15 2 10 7 10 Yb ---------- 1.5 5 1 5 2 10 

1. 	 Lithic graywacke, Weiders Member of the Shawangunk Formation, 5 ft above base of t~e Shawangunk Formation (measured section 3, unit 3), abandoned Lehigh and New. England Railroad grade, Lehigh Gap, Northamp~on Count~, ~a. Figure 4 is photomicrograph of sample. 2. 	 Dark-gray siltstone, Mmsi Member of the Shawangunk Formation, 102 ft above base of the Shawangunk Formation (measured section 1 unit 11), roadcut along U.S. Interstate 80, Delaware Water Gap: Warren County, N.J. 

3. 	 Orthoquartzite, Lizard Creek Member of the Shawangunk Formation, 860 ft !lbove the base of the. Shawangunk Formation (measured section 3, umt 43), abandoned Lehigh and New England Railroad grade, Lehigh 

Gap, Carbon County, Pa. 

4. 	 Very fine grained hematitic graywacke, Lizard Creek Member of the Shawangunk Formation, 1,000 ft above the base of the Shawangunk Formation (measured section 3, unit 54), abandoned Lehigh and New England Railroad grade, Lehigh Gap, Carbon County, Pa. 5. 	 Fine-grained phosphatic siliceous protoquartzite, Lizard Creek Member of the Shawangunk Formation, 508 ft above the base of the Shawan­ gunk Formation (measured section 1, unit 46), roadcut along U.S. Interstate 80, Delaware Water Gap, Warren County, N.J. Figure 11 is photograph of outcrop. 

6. 	 Calcareous and chloritic sandstone and siltstone with nodules of collo­ phane and siderite, Lizard Creek Member of the Shawangunk Forma­ tion, 1,280 ft above the base of the Shawangunk Formation (measured section 3, unit 69), roadcut along Pa. Route 45, Carbon County, Pa. Figure 18A shows sample. 

according to them, these units lose their identity 

and merge into the Shawangunk Formation. Detailed 

mapping by Epstein and Epstein (1967, 1969), 

Drake, Epstein, and Aaron ( 1969), and Epstein 

(1972 and unpub. data), has shown that the Clinton 

Formation of Swartz and Swartz (1931) (Lizard 

Creek Member of the Shawangunk Formation of 

this report) can be traced from the Lehigh Gap area 

eastward to Delaware Water Gap and that there it 

forms a tongue in the Shawangunk (fig. 2). Similarly, the Tuscarora of Swartz and Swartz (1931) 

(Weiders and Minsi Members of the Shawangunk 

Formation of this report) can be traced beneath the 

Clinton. Because the name Shawangunk has priority 

over the Tuscarora (named by Darton and Taff in 

1896) and Clinton (named by Conrad, 1842), the 

Shawangunk Formation is used in the area of this 

report for rocks above the Martinsburg Formation 

and below the Bloomsburg Red Beds. The names 

Clinton and Tuscarora are abandoned in the area of 

this report for reasons given in the discussion of the 

Lizard Creek Member. 

The Shawangunk is 1,632 feet thick at Lehigh 

Gap. In the Delaware Water Gap, about 1,390 

feet was measured along U.S. Interstate 80 (Epstein, 

1971). However, because of the extremely irregular 

contact with the overlying Bloomsburg Red Beds, the 

thickness can be as great as 2,100 feet. This may 

account for the wide variation of reported thicknesses at Delaware Water Gap: Chance (1882), 

1,565 feet; Grabau (1913), 1,900 feet; Swartz and 

Swartz (1931), 1,823 feet; Willard (1938), 2,000 

feet. WElDERS MEMBER 

The type section of the Weiders Member is along 

the abandoned Lehigh and New England Railroad 

in Lehigh Gap (fig. 1), Palmerton quadrangle, 

Northampton County, Pa. The member is named for 

Weiders Crossing about 1,000 feet south of the gap. 

The W eiders Member consists predominantly of 

crossbedded and planar-bedded conglomerate and 

quartzite (fig. 3). Large quartz pebbles distinguish 

the Weiders from the overlying Minsi Member. The 

contact between the two members is the top of the 

highest bed containing pebbles more than 2 inches 

long, a characteristic that is readily mapped in the 

report area. 

The Weiders Member is well exposed at the type 

section in Lehigh Gap and at Bake Oven Knob and 

Little Gap. Good exposures are found at many places 

between these localities where the member forms 

cliffs and steep dip slopes on the south side of Blue 

Mountain. In the southwestern part of the Lehighton quadrangle, the Weiders, repeated by faulting, 

holds up narrow ridges as much as 50 feet high on 

top of Blue Mountain. 

The Weiders Member has been mapped for a distance of 19 miles, and float of the member has been 

found along U.S. Route 309, 4 miles southwest of 

Bake Oven Knob. Its extent farther southwest is 

unknown. A cursory examination of equivalent beds 

at Schuylkill Gap, 21 miles southwest of Bake Oven 
SHAWANGUNK FORMATION 3 

:PALM·E·Rio r\i: ...... ... ... 

········ 

.. ... . 

.... . . 

4 MILES 

75°15' 

:sTROUDSBURG:: 

.....•. 

::s:tro:uctstiurg: : : 

EXPLANATION 

Rocks of Silurian 

~ 

~ 

and Devonian age 

Shawangunk Formation of 

Late Ordovician(?) and Silurian age 

Rocks of Cambrian and Ordovician age 

FIGURE !.-Generalized geologic map showing outcrop belt of the Shawangunk Formation in eastern Pennsylvania and 

northwestern New Jersey and 71h-minute quadrangle coverage. 

BAKE OVEN KNOB LEHIGH GAP LITTLE GAP 

I I 

GAP WIND GAP DELAWARE WATER GAP 

2000 

1500 

1­

w 

~ 

~ 

vi 

(f) 1000 w 

z 

:.::: 

u 

:C 

1­

500 

0 

"0 

~ · ·--· ·---· · ·---LIZARD CREEK MEMBER N Red beds ~ :.::: "'-. ·--· ·--.. --.. --· · --·. ·--· ·--··-·· --·-·· --·--··---· ··- ··-··--··---··-··-· z ~ == ::::J 

en .... -·· --··--··-- · · --·· --· ·--·· --· · --··--· · -Nodule beds/-·· 

36 32 28 24 20 16 12 4 


DISTANCE, IN MILES 


FIGURE 2.-Stratigraphic section of the Shawangunk Formation between Delaware Water Gap, N.J., and Bake Oven Knob, 

Pa. (modified from Epstein and Epstein, 1967, fig. 4). 

Knob, indicates that pebbles at that locality are less sive and planar bedded; beds are as much as 3 feet 

than 2 inches long. Consequently, the Weiders does thick. The pebbles and cobbles are subrounded to 

not extend to the Schuylkill. rounded and consist of quartz, chert, and sandstone. 

Conglomerates in the Weiders are generally mas- At Lehigh Gap they are as much as 3 inches long; 

0 
4 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

FIGURE 3.-Interbedded planar-bedded conglomerate and 

crossbedded medium- to very coarse grained quartzite in 

the Weiders Member of the Shawangunk Formation, Lehigh 

Gap. Rounded to subangular white quartz and dark-gray 

chert pebbles and cobbles are as much as 3 inches long. 

they are largest at Lehigh Furnace Gap (fig. 1) where 

quartz cobbles are as much as 6.5 inches long. At 

several other localities, 4-inch cobbles are not uncommon. In general, the rock breaks through the 

pebbles, except for the basal 2.3 feet (exposed only 

at Lehigh Gap) where the rock is leached of cement 

(weathered to moderate brown (5YR 4/4)1 to darkyellowish orange (10YR 6/6)), and the pebbles are 

easily removed from the matrix. Flattened mud galls 

as much as 8 inches long are scattered throughout 

the member. In general, vein quartz is the most 

abundant pebble type, especially in the upper part 

of the unit where it makes up more than 70 percent 

of the pebbles. and cobbles greater than SJ.t inch in 

length. Near the bottom of the W eiders, siliceous 

sandstone pebbles are abundant and make up more 

than 70 percent of the pebbles in the basal bed. Chert 

pebbles generally do not exceed 2 inches in length 

and make up about 20-50 percent of the pebbles 

throughout the Weiders. Mud galls and shale chips 

do not constitute more than 10 percent of the larger 

pebbles, but argillite rock fragments less than half 

an inch long may account for as much as 15 percent 

1 All rock colors were determined from the Rock-Color Chart (Goddard and others, 1948). 

FIGURE 4.-Photomicrograph (crossed polarizers) of lithic 

graywacke, Weiders Member of Shawangunk Formation, 

5 feet above base of Shawangunk at abandoned Lehigh and 

New England Railroad grade, Lehigh Gap, Northampton 

County, Pa., measured section 3, unit 3. The framework 

grains make up 72 percent of the rock and are quartz (Q), 

vein quartz (vq), chert (C), and quartzite (not seen in 

photograph) 54 percent; and rock fragments (R, mostly 

shale) , 18 percent. The remaining 28 percent of the rock 

consists of a fine-grained matrix of muscovite, quartz, and 

biotite. Very light green spherulitic chlorite (ch) fills a few 

pores. Some rock fragments have indistinct borders (at X) 

and are partly drawn out parallel to rock cleavage (cl). 

Chemical analysis of this sample is given in table 1, sample 

1. 

of the pebbles of some beds. Polymictic conglomerates are most common in basal beds. 

The matrix of the conglomerates is similar to the 

interbedded quartzites. The quartzites are mediumdark-gray (N4) to medium-light-gray (N6) and 

greenish-gray (5GY 6/1) medium- to very coarse 

grained conglomeratic sandstones in beds 1 inch to 

6 feet thick. The quartzites are evenly to unevenly 

bedded; many beds are planar. Planar and trough 

crossbedding are common. Lentils, no more than a 

few feet long, are common. In a few places ripple 

marks have wavelengths of as much as 2 feet. 

Limonite and hematite specks and sand-sized grains 

of grayish-orange (10YR 7/4)-weathering shale are 

scattered throughout most beds. In thin section, the 

quartzites contain 47 to about 85 percent quartz, 

chert, and sandstone grains. Quartz grain contacts 

are generally sutured, although silica overgrowths 

are common. Quartz generally occurs as single grains 

with slight to strong undulose extinction. Bubble 

trains and vermicular chlorite inclusions are very 

common. The matrix of the quartzites is composed 

predominantly of quartz and muscovite with a 

small amount of chlorite. It forms about 9-37 per­
WElDERS MEMBER 5 

cent of most rocks. Feldspar is rare. The quartzites 

in the Weiders Member are, therefore, lithic graywackes, siliceous subgraywackes, and siliceous protoquartzites; the less mature varieties are more abundant toward the base of the member (fig. 4). Orthoquartzites containing more than 97 percent quartz 

are rare. 

Heavy minerals in the quartzites are chiefly muscovite and rounded to euhedral zircon and tourmaline. Biotite is rare, and only one grain of hornblende was seen. Slightly pleochroic very light green 

spherulitic chlorite fills pore spaces in several 

samples. 

Greenish-gray (5GY 6/1) argillite (indurated 

claystone and siltstone) beds occur but nowhere 

abundantly. They are lenticular and generally from 

0.5 to 7 inches thick, although a 2-foot-thick bed is 

present at Lehigh Gap. 

Basal beds of the W eiders Member rest abruptly 

and with angular discordance on shale and grayFIGURE 5.-lnterbedded quartzite and quartz- and chert-pebble conglomerate in the Minsi Member of the Shawangunk 

Formation at the type section, Delaware Water Gap, Warren County, N.J. Note channels at bases of many of the 

beds. 

458-355 0 - 72 - 2 

wacke of the Pen Argyl Member of the Martinsburg 

Formation. Fault gouge, breccia, and slickensides 

indicate that the interval at and just below the contact is also a zone of detachment (Epstein and 

Epstein, 1969). 

The contact between the Weiders and overlying 

Minsi Member is the top of the highest bed containing pebbles more than 2 inches long. Defining the 

top of the member in this way, the Weiders is 189 

feet thick at the type section in Lehigh Gap and 

about 50 feet thick at Bake Oven Knob. The thickness varies according to the presence or absence of 

pebbles more than 2 inches long. At Bake Oven Knob, 

for example, the top 6 inches of the upper 39 feet is 

coarsely conglomeratic. If this bed were missing, the 

Weiders would be only 11 feet thick there. The 

W eiders is apparently thickest (about 220 ft on the 

basis of construction of cross sections) at Little Gap. 

MINSI MEMBER 

The Minsi Member of the Shawangunk Formation 

is named for Mount Minsi, overlooking Delaware 

Water Gap, Monroe County, Pa. The type section is 

along U.S. Interstate 80 in Delaware Water Gap, 

Warren County, N.J. (figs. 1 and 19) ; there the 

Minsi contains quartzite, conglomerate (with quartz, 

chert, and sandstone pebbles less than 2 inches long), 

and minor amounts of siltstone (fig. 5). It forms a 

cliff along the middle of the south slope of Blue and 

Kittatinny Mountains northeast of Smith Gap. 

Southwest of Smith Gap, the Minsi forms the break 

FIGURE 6.-Crossbedded and planar-bedded conglomeratic 

quartzite and quartzite containing quartz pebbles not more 

than 1 inch long, Minsi Member of the Shawangunk Formation, Delaware Water Gap, roadcut along U.S. Interstate 80, Warren County, N.J. 
6 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

in slope at the top of Blue Mountain. It is 303 feet 

thick at its type section and thins gradually to 225 

feet at Lehigh Gap (fig. 2). 

In the Delaware Water Gap, the Minsi consists of 

light-gray (N7) to medium-dark-gray (N4) and 

light-olive-gray (5Y 6/1) medium- to very coarse 

grained crossbedded to planar-bedded locally rippled 

limonitic pyritic unevenly to moderately evenly 

bedded and lenticular (beds 1 inch to more than 

3 feet thick) thin- to thick-bedded quartzite, conglomeratic quartzite, and quartz-, chert-, and 

argillite-pebble conglomerate (fig. 6). Some quartz 

pebbles are nearly 2 inches long, but most are less 

than 1 inch long. Argillite pebbles are mostly flattened shaly siltstone and are as much as 4 inches 

long. About 7 percent of the Minsi is dark-gray (N3) 

to light-olive-gray (5Y 6/1) siltstone that is locally 

shaly and mud cracked. The siltstone is in lenticular 

beds as well as short lenses less than 1 inch to 1 foot 

FIGURE 7.-Photomicrograph (crossed polarizers) of poorly 

sorted, conglomeratic, fine- to medium-grained feldspathic 

sandstone from lowest exposed bed of the Minsi Member of 

the Shawangunk Formation, Delaware Water Gap, Portland quadrangle, New Jersey (measured section 1, unit 2). 

Matrix minerals (13 percent) are not readily identified but 

appear to consist mainly of muscovite and quartz with 

minor chlorite, limonite, and hematite. Framework grains 

are quartz ( Q, 80 percent), as much as 5 mm long, sericitized potash feldspar (F, 5 percent), partly perthitic and 

as much as 1 mm long, and chert (2 percent). Many quartz 

grains are composite with sutured contacts (sq). Grains 

are angular to subround. Quartz-grain contacts are straight 

or concave with (at 1) or without (at 2) a clay coating, 

or are overgrown with optically continuous quartz (at 3). 

The quartz contains abundant vacuole inclusions. The 

heavy-mineral suite is mature and consists of subhedral to 

rounded zircon and subordinate tourmaline and rutile. One 

grain tentatively identified as monazite is included in a 

quartz grain. Rock fragments (shale) are not common (< 

1 percent). 

thick. A chemical and semiquantitative spectrographic analysis of a typical siltstone is given in 

table 1, sample 2. 

The contact of the Minsi with the Martinsburg 

Formation is not presently exposed at Delaware 

Water Gap, but Beerbower (1956) described it as 

abrupt and unconformable. The angular unconformity between the Shawangunk and Martinsburg 

Formations is indicated by mapping in the area 

(Drake and others, 1969; Epstein, 1971, 1972). An 

abrupt unconformable contact is exposed 5 miles 

northeast of Delaware Water Gap at the Yards Creek 

hydroelectric project on Kittatinny Mountain north 

of Blairstown, N.J. (Epstein and Epstein, 1969, p. 

169). There the Minsi Member rests on the middle 

member (Ramseyburg) of the Martinsburg Formation; accordingly, more than 5,000 feet of rock are 

missing at the unconformity (Drake and Epstein, 

1967). The contact between the Ramseyburg and 

overlying Pen Argyl Member of the Martinsburg 

emerges from beneath the Shawa·ngunk 1.2 miles 

southwest of Delaware Water Gap (Epstein and 

Epstein, 1969, p. 201). 

The Minsi Member is uniformly similar throughout its outcrop. West of Smith Gap, it overlies and 

interfingers with the W eiders Member and probably 

extends for many miles southwest of Bake Oven 

Knob, probably to and beyond Schuylkill Gap, where 

it was mapped as the Tuscarora Sandstone by Wood, 

Trexler, and Kehn (1969). 

FIGURE 8.-Mud-cracked shaly siltstone, Minsi Member of the 

Shawangunk Formation. Underside of bed exposed about 

60 feet above U.S. Interstate 80 at south entrance of Delaware Water Gap, Warren County, N.J. (measured section 

1, unit 9). Mud-crack polygons about 1 foot across. 
LIZARD CREEK MEMBER 7 

The sandstones or quartzites of the Minsi Member 

are submature (matrix averages about 12 percent in 

the thin sections studied). At Delaware Water Gap, 

they contain 3-5 percent feldspar and are classed as 

feldspathic sandstones (fig. 7). Fragments of shale 

and siltstone generally form less than 2 percent of 

the rock. The quartz grains are sutured or have silica 

overgrowths. Single grains are most common, but 

many are composite and stretched, indicating a 

partly metamorphic or presolved sedimentary 

quartzite source. The heavy-mineral suite is mature 

and includes mostly zircon, subordinate tourmaline, 

and rare rutile. These minerals are well rounded to 

subhedral, and their association with quartz grains 

containing small inclusions of biotite and vermicular 

chlorite, as well as clastic grains of orthoclase, suggests a reworked sedimentary source with possibly 

minor contributions from a granitic terrane containing quartz veins. Conceivably, the total mineral assemblage could have been derived directly from a 

sedimentary source whose rocks themselves were derived from a complex source area. Labile minerals, 

such as hornblende, are extremely rare. West of 

Delaware Water Gap, feldspar was not seen in thin 

section, and the rocks at Lehigh Gap, for example, 

are mainly siliceous protoquartzites. 

The siltstones in the Minsi are made up of medium 

to very coarse silt-sized angular quartz grains and 

a few chert grains floating in a matrix of muscovite 

and subordinate chlorite. Argillaceous rock fragments are rare. The siltstones are generally sandy 

and laminated, features best seen on polished surfaces. Mud cracks were seen in one siltstone bed at 

Delaware Water Gap (fig. 8). 

LIZARD CREEK MEMBER 

The sequence of siltstone, shale, sandstone, and 

scattered red beds, conglomeratic and calcareous 

sandstone, and other lithic types that are herein 

named the Lizard Creek Member of the Shawangunk 

Formation have been included in the Clinton Formation by most previous workers in eastern Pennsylvania. The underlying coarse clastic rocks herein assigned to the W eiders and Minsi Members were 

placed in the Tuscarora Sandstone west of Lehigh 

Gap. We are abandoning the names Clinton and 

Tuscarora in the area of this report. The historical 

development of nomenclature of these rocks has been 

confused. (See summaries by Schuchert, 1916; 

Swartz, 1923 ; and Swartz and Swartz, 1931.) The 

following are pertinent details for purposes of this 

discussion : 

The Shawangunk was named by Mather in 1840 

for rocks exposed in the Shawangunk Mountains in 

southeastern New York. The Shawangunk was 

shown to extend in outcrop across northern New 

Jersey to Delaware Water Gap by Weller (1903). 

The Tuscarora Sandstone was named by Darton and 

Taff (1896), presumably for Tuscarora Mountain in 

south-central Pennsylvania. The name Clinton was 

first used by Conrad ( 1842) for exposures near 

Clinton, N.Y. It was later applied by White (1882) 

to the red beds at Delaware Water Gap which are 

now called Bloomsburg and which overlie rocks that 

were subsequently called Clinton by Swartz and 

Swartz (1931). Swartz (1923) raised the Clinton 

to group rank in Maryland and included in it, in 

ascending order, the Rose Hill Formation, Keefer 

Sandstone Member at the base of the Rochester, and 

Rochester Formation. The Tuscarora Sandstone, 

Rose Hill, Keefer, and Rochester were traced with 

some degree of uncertainty northeastward from 

Maryland by Swartz and Swartz (1931) to Swatara 

Gap, 30 miles southwest of Bake Oven Knob. From 

Swatara Gap east to Lehigh Gap, the Swartzes were 

unable to recognize the formations of their Clinton 

Group, and they designated the unit the Clinton 

Formation. From Lehigh Gap east to Delaware 

Water Gap, they were unable to differentiate the 

Clinton Formation from the subjacent Tuscarora 

Sandstone. Consequently, they dropped the names 

Clinton and Tuscarora and recognized the combined 

interval as the Shawangunk Formation at Delaware 

Water Gap. 

The Swartzes' usage has been partly accepted on 

FIGURE 9.-Evenly bedded siltstone, shale, and quartzite in 

the Lizard Creek Member of the Shawangunk Formation 

in roadcut along Pa. Route 145, Lehigh Gap, just north of 

Aquashicola Creek. Thickest quartzite bed is about 1.5 

feet thick. 
8 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

the geologic map of Pennsylvania (Gray and others, 

1960)-the name Shawangunk is applied to those 

rocks east of Swatara Gap and the names Tuscarora 

and Clinton are used to the west, on the assumption 

that use of the Clinton is limited to those areas where 

the Rose Hill, Keefer, and Rochester could be distinguished. To the east, where the Clinton could not 

be so divided, it is combined with the Tuscarora to 

form the Shawangunk. However, in two 71/2-minute 

quadrangles immediately west of Swatara Gap, 

Wood, Trexler, and Kehn (1969) could not divide the 

Clinton into mappable units, but nonetheless retained the name Clinton and mapped the Tuscarora 

Sandstone below it. 

As mentioned previously, the Clinton, as defined 

by Swartz and Swartz ( 1931), at Lehigh Gap was 

placed in the Shawangunk Conglomerate (now 

Formation) and informally termed the "quartziteargillite unit" by Epstein and Epstein (1967, 1969). 

This unit extends eastward to Delaware Water Gap 

and there intertongues with two quartzite and conglomerate units (the Minsi and Tammany Members 

of this report). Because the name Clinton had had 

widespread usage, it was recently retained as the 

name for a member in the Shawangunk (Epstein, 

1971), although this usage was not adopted by the 

U.S. Geological Survey. Because these rocks do not 

meet the tripartite division of the Clinton recognized by Gray and others ( 1960), the Clinton is 

herein abandoned for use in eastern Pennsylvania, at 

least east of Bake Oven Knob. This usage agrees 

with current practice of the Pennsylvania Geological 

Survey (D. M. Hoskins, oral commun., 1971). InterFIGURE 10.-Laminated, well-sorted, fine-grained calcitic 

sandstone in the Lizard Creek Member (measured section 

1, unit 35), Delaware Water Gap. Primary current lineation 

(not readily apparent in photograph) is present on the 

upper bedding surface and parallels the dip of the laminae. 

Small ridges on bedding surface are not ripples but offsets 

of small soft-rock faults (arrow). The rock is believed to 

be a beach or barrier-bar deposit, and the faults may have 

formed parallel to the ancient strand line. (See section on 

environments of deposition.) 

estingly, the name Clinton was not applied to coeval 

rocks in southeastern New York (Fisher, 1959) that 

are part of the outcrop belt that extends into Pennsylvania. Thus, in eastern Pennsylvania, the Clinton 

Formation of previous usage is the Lizard Creek 

Member of the Shawangunk Formation of this report, and the Tuscarora Sandstone is the Weiders 

and Minsi Members. 

The Lizard Creek Member of the Shawangunk 

Formation is named for Lizard Creek, which joins 

the Lehigh River 3 miles west of Lehigh Gap. The 

type section is in Lehigh Gap, where the member is 

1,225 feet thick. Schuchert (1916) believed that the 

member (his "Upper Shawangunk") is 900 feet 

thick at Lehigh Gap, and Swartz and Swartz (1931) 

measured 1,093 feet for their equivalent Clinton. 

The Lizard Creek has been mapped east from Bake 

Oven Knob to the Delaware Water Gap area where 

it thins to 273 feet. It is nearly completely exposed 

at Lehigh Gap and at Delaware Water Gap, but only 

the lower 172 feet is exposed at Wind Gap; elsewhere 

in the area it is generally very poorly exposed. 

FIGURE 11.-Flaser-bedded (ripple lensing) and lenticular 

fine-grained sandstone (light) irregularly interbedded with 

burrowed shaly siltstone (dark). Load casts show as sole 

markings in many of the sandstones. Black phosphate 

nodules, as much as 1.5 inches long, are scattered throughout; these nodules weather dull white. The nodules are 

angular, and some have a partial mud rind. These beds 

were probably reworked by storm waves while the sediment 

was still soft (see section on environments of deposition). 

Sample 5, table 1, is a chemical and semiquantitative spectrographic analysis of a rock from this unit. Hammer head 

gives scale. Lizard Creek Member of the Shawangunk Formation, Delaware Water Gap, Warren County, N.J. (measured section 1, unit 46). 
LIZARD CREEK MEMBER 9 

The Lizard Creek Member is characterized by 

interbedded sandstone, siltstone, and silty shale (figs. 

9 and 19). It is gradational into the underlying Minsi 

Member but is readily differentiated because of its 

abundant medium- to dark-gray siltstone and shale. 

The sandstones in the Lizard Creek are generally 

fine to medium grained but range from very fine to 

very coarse grained and locally are conglomeratic or 

FIGURE 12.-Convolutions (ball-and-pillow structure) due to 

soft-rock slumping, in very fine grained sandstone and siltstone. Note overturned and refolded flow fold at top. Negative print of acetate peel. Lizard Creek Member of the 

Shawangunk Formation, Delaware Water Gap, N.J. 

(measured section 1, unit 43). 

FIGURE 13.-Asymmetric ripples in fine-grained sandstone, 

Lizard Creek Member of the Shawangunk Formation, 

Delaware Water Gap, Warren County, N.J. (measured 

section 1, unit 35). The ripples have wavelengths of about 

3.5 inches and amplitudes of 0.5 inch. 

silty. Quartz pebbles are as much as 0.5 inch long. 

Sorting is fair to good. Most sandstones are limonitic, a few have carbonate cement, and some contain rare specks of graphite, about 2 mm in diameter. They are evenly to unevenly bedded, laminated 

(fig. 10) to thick bedded (beds range from less than 

0.5 to 8.5 feet thick), and also are in discontinuous 

lenses (fig. 11). Some beds contain convolutions (fig. 

12). Thin shale intercalations and flat argillite clasts 

(clay galls) as much as 4 inches long are numerous. 

The sandstones are planar bedded to crossbedded, 

and a few are rippled (fig. 13). Both trough and 

planar crossbeds are common. Crossbed sets range 

from less than 0.5 inch to more than 2 feet thick. 

Colors on fresh surfaces are generally very light 

gray (N8) to medium dark gray (N4) and light 

olive gray ( 5 Y 6I 1) , but some sandstones are light 

greenish gray (5GY 8/1) to moderate greenish gray 

(5GY 5/1), very light bluish white (5B 8/1) to light 

bluish gray (5B 7/1), light brownish gray (5YR 

6/1), and yellowish gray (5Y 8/1). They weather 

shades of gray and very pale orange (10YR 8/2), 

light brown (5YR 6/4), moderate brown (5YR 4/4), 

FIGURE 14.-Photomicrograph (crossed polarizers) of finegrained quartzite, Lizard Creek Member of the Shawangunk 

Formation, Delaware Water Gap, N.J. (measured section 

1, unit 35). Quartz (Q) and minor chert (86 percent) are 

the dominant minerals in a muscovite and chlorite matrix. 

Some matrix is entirely recrystallized to chlorite (pennine). 

Note the straight to interlocking contacts between quartz 

grains. Limonite-stained carbonate (probably calcite, Ca) 

forms a cement in some areas and makes up about 4 percent of the rock. Minor potash feldspar (< 1 percent) and 

rock fragments (shale, about 1 percent) were noted. Heavy 

minerals are fairly abundant and include subrounded to 

rounded tourmaline (T), zircon (Z), and lesser rutile. The 

composition of the rock is near the borderline between a 

protoquartzite and orthoquartzite. Figure 10 is a photograph of the rock sample. 
10 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

to dark yellowish orange (10YR 6/6). The sandstones are in sharp to gradational contact with beds 

above and below. Many basal surfaces are filled 

channels of low relief. 

As seen in thin section, the sandstones range from 

lithic graywackes to orthoquartzites (fig. 14). Sorting is poor to excellent. Quartz ranges from more 

than 95 percent to less than 50 percent of the sand 

fraction of the rock. Sample 3, table 1, is the chemical and semiquantitative spectrographic analysis of 

a typical orthoquartzite. Most quartz is in single 

grains with undulose extinction, although nearly 

every thin section examined contained scattered composite grains derived from preexisting quartzite. 

Chert is ubiquitous, generally making up less than 

5 percent of the grains. Where quartz grains are in 

contact, their borders are sutured. Quartz overgrowths are common, and calcite and light-green 

spherulitic chlorite form pore fillings or replace 

quartz in many samples. Sand-size muscovit.e grains 

are common, and biotite grains, partly altered to 

chlorite, were seen in many samples. Matrix minerals are mostly fine-grained muscovite and quartz, 

with subordinate chlorite. They range in volume 

from thin clay coatings on larger clastic grains to 

more than half the rock. The heavy-mineral suite 

forms as much as 2 percent of some rocks and is 

dominated by round to subround zircon and tourmaline grains. Leucoxene, limonite, black opaque minerals {probably magnetite), and hematite are also 

FIGURE 15.-Feeding burrows on bedding plane of siltstone 

in Lizard Creek Member of the Shawangunk Formation, 

Delaware Water Gap, Warren County, N.J. (measured 

section 1, unit 31). 

common. The limonite and hematite are mostly alteration products of iron-bearing minerals, such as 

chlorite and biotite. Rock fragments, mostly shale 

and siltstone, are locally absent but make up more 

than 3 percent of some beds. In some rock fragments, there is good preferred alinement of micasthese may be meta-argillites. 

Beds of finer clastic rocks in the Lizard Creek 

are shaly and sandy siltstone and silty shale. Siltand sand-size grains of mica are common on bedding 

planes. The fine-grained rocks are medium light 

gray (N6) to grayish black (N2), light olive gray 

(5Y 6/ 1) to medium olive gray (5Y 5/1), greenish 

gray (5GY 6/ 1) to dark greenish gray (5GY 4/1), 

and rarely, light bluish gray (5B 7 / 1) on fresh surfaces. They weather various shades of gray, green, 

orange, brown, and pink. They are indistinctly 

bedded to laminated; beds range in thickness from 

less than 0.5 to more than 6 feet. Many of the finegrained rocks are irregularly laminated, lenticular, 

cross laminated, flaser bedded, and have small-scale 

scour and fill. Subordinate lenses of fine- to mediumgrained sandstone are common. Many siltstones and 

shales are burrow mottled. Discrete burrows are 

generally circular, 0.25-0.5 inch in diameter, and 

may be perpendicular or parallel to bedding (fig. 

15). At Delaware Water Gap, some vertical sandfilled burrows are 1 inch in diameter and as much as 

1 foot deep. Olive-gray shales are common above 

the lower 150 feet of the Lizard Creek Member at 

Lehigh Gap but are absent at Delaware Water Gap 

and Wind Gap. Most of these are unevenly laminated 

to flaser bedded. 

The Lizard Creek Member contains scattered redbed intervals, not more than 7 feet thick, consisting 

of sandstone, siltstone, and shale. They are not found 

east of Smith Gap (fig. 2). The sandstones are dusky 

red purple (5RP 3/ 2) and grayish red purple (5RP 

4/2) to brownish gray (5YR 4/1) and may be color 

laminated or mottled with moderate greenish gray 

(5GY 5/ 1) to dark greenish gray (5G 4/1). Most are 

silty and very fine to fine grained, although a few 

are coarse grained. Most of the finer grained red 

sandstones are hematitic graywackes with abundant 

rock fragments, muscovite, and biotite. (See sample 

4, table 1, for chemical and semiquantitative spectrographic analysis.) The hematite and fine-grained 

muscovite-quartz matrix forms more than 30 percent of the rock. These sandstones are transitional 

into grayish-red-purple (5RP 4/ 2) to moderate-redpurple (5RP 5/ 2) and pale-red ( 5R 6/ 2) shaly and 

sandy siltstones that are color mottled and interlaminated with similar rocks that are moderate 
LIZARD CREEK MEMBER 11 

greenish gray ( 5G Y 5I 1) and light brownish gray 

(5YR 6/1). The mottling is due to burrowing of 

organisms, the remains of which have not been 

found (fig. 16). 

FIGURE 16.-Vertical burrow disrupts laminae in hematitic 

shaly siltstone to fine-grained sandstone. The laminae have 

been completely churn-burrowed in the lower part and in 

other parts of the sample. Negative print of thin section. 

Lizard Creek Member of the Shawangunk Formation, Lehigh Gap, Northampton County, Pa. (measured section 3, 

unit 40). 

FIGURE 17.-Photomicrograph (crossed polarizers) of moderately sorted fine-grained hematitic orthoquartzite. The 

rock is made up predominantly of single-crystal quartz 

grains (Q) (about 95 percent) . Rare shale and siltstone 

rock fragments (R), vein quartz (vq), chert (C), and 

rounded tourmaline (T) make up the remainder. Most 

quartz grains have a thin coating of hematite which shows 

the outline of the detrital grain adjacent to silica overgrowths (arrow). Lizard Creek Member of the Shawangunk 

Formation, Lehigh Gap, Northampton County, Pa. (measured section 3, unit 67). 

Some of the red sandstones are hematitic orthoquartzites and are strikingly different from the graywackes in thin section. The orthoquartzites are fine 

to coarse grained and generally well sorted (fig. 17). 

Intermediate red siliceous protoquartzites are also 

present, indicating that the sorting capabilities of 

the transporting media and the depositional environments were varied. 

In the upper half of the Lizard Creek Member at 

the type section in Lehigh Gap, generally in the 

upper 380 feet, there are more than 12 beds, 2-8 

inches thick, of irregularly laminated sandstone to 

silty shale containing ovoid and irregular nodules of 

siderite, collophane, and chlorite; quartz pebbles; 

phosphatic siltstone and shale intraclasts; and fragments of linguloid brachiopods (fig. 18). The siderite 

nodules are generally elliptical, 2-20 mm long, are 

dark yellowish orange (lOYR 6/ 6) to pale yellowish 

orange (lOYR 8/ 6), and may be rimmed with or 

partly replaced by dark-yellowish-green (lOGY 4/4) 

chlorite. Green pleochroic chlorite also fills interstices ; replaces other minerals, linguloid brachiopod 

shells, and possibly pellets; and occurs as nodules. 

Chlorite grains in the Lizard Creek have low birefringence, are optically homogeneous, and have a 

strong 14 A reflection on X-ray diffractograms and 

are, therefore, not chamosite. Chamosite, however, 

has been found in concentrically banded oolites in 

ironstones of the Clinton Group of New York, Ohio, 

and West Virginia (Alling, 1947; Hunter, 1960, 

1970; and Schoen, 1964). Some of the chlorite in the 

Lizard Creek may have originally been chamosite 

that was altered during low-grade metamorphism to 

chlorite (James, 1966), for high 7 A/14 A peakheight ratios (as much as 5:1 in some samples) 

indicate that the chlorite is iron rich. X-ray diffraction analysis indicates that the collophane is carbonate fluorapatite. The collophane is grayish black 

(N2) to dark gray (N3) and may weather dull 

white, especially in the linguloid fragments. Some of 

the phosphatic siltstone intraclasts are as much as 

3.5 inches long and are flattened parallel to the 

bedding; many are spherulitic. In general, the nodule 

beds are between laminated sandstones, siltstones, 

or shale (fig. 18). 

The nodule-bearing beds were not seen in the incompletely exposed Lizard Creek at Wind Gap, but 

at Delaware Water Gap they are present between 

205 and 258 feet above the base of the member. They 

differ from the beds at Lehigh Gap by containing 

black (Nl) to grayish-black (N2) dull whiteweathering rounded and irregular phosphate nodules 

as much as 1.5 inches long (fig. 11). Neither siderite 
12 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

A B 

FIGURE 18.-Nodule beds in the Lizard Creek Member of the Shawangunk Formation, Lehigh Gap, Pa. A, Nodules and 

oolites of carbonate fluorapatite (1), carbonate fluorapatite rimming iron-rich shale pebbles (2), quartz pebbles as much as 

8 mm long (3), .and shale pebbles (4) that were probably ripped up from substrate similar to the shale at 5. This nodule 

bed lies between laminated well-sorted medium-grained quartzite. The shale and phosphate nodules may have been deposited 

in the reducing environment of a lagoon and washed onto a sandbar during a storm. Chemical analysis of the shale (5) 

shows it to contain 8.2 percent iron expressed as Fe20a and 0.19 percent P205. Sample 6, table 1, is a chemical and semiquantitative spectrographic analysis of this rock. Photograph of polished section from measured section 3, unit 72. B, 

Nodules of siltstone partly replaced by collophane (1), siderite (2) rimmed with chlorite (3) and penetrated by quartz 

grain (4) (showing that the nodule was soft at time of deposition), and fragments of linguloid brachiopods (5). Note 

lapping of irregularly laminated shale and very fine grained sandstone on large siltstone clast (6). Serial sections of the 

siltstone clasts show that they are extremely irregular in shape, suggesting deposition while the siltstone was wet and 

plastic. Negative print of acetate peel from measured section 3, unit 66. 

nor chlorite nodules nor fragments of linguloid mation is herein named for Mount Tammany overbrachiopods were found at Delaware Water Gap. looking Delaware Water Gap, Warren County, N.J. 

Parts of the Lizard Creek Member are rich in (fig. 1). The type section is in Delaware Water Gap 

iron (some samples contain nearly 10 percent total (fig. 19); there, along U.S. Interstate 80 in New 

iron). Much of the iron is contained in hematite, 

magnetite, goethite, lepidocrosite, iron-rich chlorite, 

and siderite. 

The boundary between the Lizard Creek and 

Tammany Members is transitional in the eastern 

half of the area and is placed at the top of the highest siltstone or shale of the mixed siltstone-shalequartzite sequence of the Lizard Creek. The contact 

can be placed at a bedding surface in exposures at 

Delaware Water Gap. In areas of nonexposure where 

the contact is mapped on float, the boundary is 

less definite. 

In the western part of the area, the upper contact 

of the Lizard Creek is placed at the base of the lowest 

red bed of the dominantly red sequence of the overlying Bloomsburg Red Beds. The Bloomsburg and 

Lizard Creek are transitional through 163 feet of 

red, green, and gray sandstone, siltstone, and minor 

shale at Lehigh Gap. 

TAMMANY MEMBER 

The Tammany Member of the Shawangunk ForJersey, the member is 816 feet thick, but thickens 

to about 1,500 feet to the northwest in the gap at 

the expense of the overlying Bloomsburg Red Beds. 

The Tammany consists of medium-gray (N5) to 

medium-dark-gray (N4) crossbedded, limonitic, 

pyritic, evenly to unevenly bedded quartzite and 

about 2-percent dark-gray shaly siltstone. Flattened 

shale pebbles are common. Quartz pebbles are as 

much as 2 inches long. The quartzites are predominantly protoquartzites (fig. 20). The sandstones of 

the Tammany Member are similar to those of the 

Minsi Member at Delaware Water Gap, except that 

feldspar is not as abundant in the Tammany (<1 

percent in thin sections examined). 

Unique dolomite beds crop out near the top of the 

Tammany Member about 400 feet south of the contact with the overlying Bloomsburg Red Beds and 

a few hundred feet north of the tollgate on U.S. 

Interstate 80 at the north end of Delaware Water 

Gap near the village of Delaware Water Gap, Pa. 

These beds are about 4 feet thick and consist of a 
TAMMANY MEMBER 13 

FIGURE 19.-The Shawangunk Formation at Delaware Water Gap, N.J. Om, Martinsburg Formation; SOsm, quartzite and 

conglomeratic quartzite of the Minsi Member; SOsl, interbedded quartzite, siltstone, and shale of the Lizard Creek Member; SOst, quartzite and conglomerate of the Tammany Member. Type section of the Minsi and Tammany Members of 

the Shawangunk Formation. The contact between the Martinsburg and Shawangunk Formations is covered by talus along 

the base of Mount Tammany. Note prominent kink fold in the Tammany Member and disharmonic folds and faults in the 

Lizard Creek Member. Beds generally dip northwest. 

lower medium-gray dolomite that weathers moderate 

brown and an upper greenish-gray dolomitic shale 

or shaly dolomite (fig. 21). The medium-gray dolomite is nearly pure ferroan dolomite (determined 

by X-ray diffraction and staining techniques). Small 

amounts of calcite, quartz, muscovite, and a 14 A 

mineral, probably chlorite, were noted on the X-ray 

trace. The rock reacts slightly with cold dilute hydrochloric acid. The greenish-gray dolomitic shale or 

shaly dolomite consists of ferroan dolomite with 

about equal amounts of muscovite, quartz, and 

chlorite. No calcite was noted, and the rock does not 

react with dilute HCI. Concretions of dolomite and 

calcite, 1/2-3 inches in diameter, with concentric 

structure, are abundant. The dolomite beds are overlain and underlain by crossbedded and planar-bedded, 

predominantly medium grained, partly conglomeratic 

quartzite and siltstone. The lower dolomite bed contains irregular patches of rock similar to the upper 

bed. In thin section, the medium-gray dolomite consists of a mosaic of slightly clouded dolomite grains 

averaging about 0.04 mm in diameter that replace 

the dolomitic shale or shaly dolomite. Ferroan dolomite occurs in scattered beds overlying and underlying this horizon, as well as in the overlying Bloomsburg Red Beds. 

The Tammany Member forms most of the crest 

of Kittatinny and Blue Mountains. It is thickest at 

Delaware Water Gap and thins southwestward as 

its quartzites and conglomerates are replaced by 

finer clastic rocks of the Lizard Creek Member (fig. 

2). Tongues from the Tammany extend into the Lizard Creek, but because beds typical of the Lizard 

Creek make up more than 50 percent of the interval 

southwest of Smith Gap, the Tammany is separated 

from the Lizard Creek at Smith Gap by an arbitrary 

cutoff. 

The upper contact of the Tammany Member is 

placed at the base of the oldest red bed of the overlying Bloomsburg Red Beds. The color boundary is 

extremely irregular, transects bedding, and rises 

about 700 feet within a horizontal distance of less 

than 1 mile in Delaware Water Gap (see fig. 2; also, 

Epstein, 1972). The lithologic contrast between the 

Bloomsburg and Shawangunk is likewise indistinct, 

so that lithologies could not be used conveniently for 

a mappable boundary. The color change was used 

because it has been the accepted method of separating the two formations (Willard, 1938, p. 10) and 

458-355 0 - 72 - 3 
14 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

because it is the most satisfactory method where 

mapping float (the contact is covered in most areas 

other than at Delaware Water Gap). 

AGE OF THE SHAWANGUNK FORMATION 

The Shawangunk Formation of eastern Pennsylvania has been regarded as Early to Middle Silurian 

in age (Swartz and others, 1942). This age assignment was based primarily on the presence of eurypterids and Arthrophycus and on regional stratigraphic considerations. The evidence appears to be 

equivocal and needs reevaluation. The base of the 

Shawangunk conceivably could be latest Ordovician 

in age. 

In central Pennsylvania, the clastic rocks immediately overlying the Martinsburg Formation are, in 

ascending order, the Bald Eagle Member of the 

Juniata Formation of Willard and Cleaves (1939), 

the Juniata Formation, and the Tuscarora Sandstone. Diagnostic fossils have not been found in the 

Bald Eagle and Juniata, and the age of these units 

is still uncertain (Willard, 1943, p. 1091; Swartz, 

1942, p. 178), although they are generally believed 

to be Maysvillian and Richmondian in age (TwenFIGURE 20.-Photomicrograph (crossed polarizers) of conglomeratic coarse-grained protoquartzite, Tammany Member of the Shawangunk Formation, Delaware Water Gap 

(measured section 1, unit 58). Framework minerals are 

quartz (Q, 80 percent), chert (C, 1 percent), rock fragments (R, shale and siltstone, 1 percent), and minor muscovite and zircon. The quartz is rutilated and contains 

abundant vacuoles and scattered inclusions of vermicular 

chlorite. The quartz grains are angular to subround, simple 

to composite, and have straight to undulose extinction. 

Grain contacts are straight to concave. The matrix ( 18 

percent) is composed of fine quartz, muscovite, and chlorite. Some areas are recrystallized to spherulitic chlorite 

(ch). Note peripheral growth of mica on some quartz 

grains. 

hofel and others, 1954). East of the Susquehanna 

River, near Harrisburg, Pa., the Bald Eagle and 

Juniata pinch out, and at the Lehigh River, the 

Shawangunk Formation, which is laterally continuous with the Tuscarora, rests directly on the 

Martinsburg Formation. For this reason, it was 

assumed that the base of the Shawangunk is Early 

Silurian in age. However, it is not unreasonable to 

believe that parts of the basal Shawangunk are correlative with rocks of the Juniata or Bald Eagle. 

Lack of diagnostic fossils in these rocks makes this 

suggestion a possibility. In southeastern New York, 

basal Shawangunk beds are believed to be Middle 

Silurian in age, but lack of key fossils makes this 

age assignment questionable (Fisher, 1959). 

Regional stratigraphic relations suggest that lowermost Silurian and uppermost Ordovician clastic 

rocks, derived from highlands uplifted during the 

Taconic orogeny, overlap underlying shales and become younger to the northeast. Thus, in central 

Pennsylvania, where deposition was uninterrupted, 

boundaries between the Reedsville Shale and the successively younger Bald Eagle, · Juniata, and Tuscarora are conformable. In eastern Pennsylvania, New 

Jersey, and southeastern New York, the Shawangunk Formation lies unconformably on the Martinsburg Formation; the hiatus presumably increases in 

duration to the northeast. (See Willard and Cleaves, 

1939.) Graptolites collected from the top of the Pen 

FIGURE 21.-Medium-gray dolomite that weathers moderate 

brown (a, about 2 ft thick) overlain by greenish-gray dolomitic shale or shaly dolomite with nodules of calcite and 

dolomite with concentric structure (b, about 1.8 ft thick). 

Hammer is at contact with overlying fine- to mediumgrained feldspathic sandstone. Tammany Member of the 

Shawangunk Formation, near tollgate on U.S. Interstate 

80, at village of Delaware Water Gap, Pa. 
AGE OF THE SHAWANGUNK FORMATION 15 

Argyl Member, the upper member of the Martinsburg Formation at Lehigh Gap, have been identified 

by W. B. N. Berry and are indicative of the upper 

subzone of zone 13 (Berry, 1970; Epstein, 1970). 

According to Berry, this subzone is equivalent to the 

Clim.acograptus spiniferus zone of Riva (1969). 

Riva showed that the C. spiniferus zone is limited to 

the lower half of the Utica Shale in the Mohawk 

Valley, N.Y., which he correlated with the Cobourg 

Limestone of Raymond (1921). On the basis of conodont studies, Sweet and Bergstrom (1971) correlated 

the Cobourg with the entire Edenian and lower 

Maysvillian of the Cincinnati area. Thus, the top 

of the Martinsburg in eastern Pennsylvania lies 

within the Edenian-early Maysvillian interval (early 

Late Ordovician). 

The Juniata-Tuscarora contact, which supposedly 

marks the Ordovician-Silurian boundary in central 

Pennsylvania, is complex and may be time transgressive (Swartz, 1942, p. 186). The two formations are 

transitional, and the contact is drawn with difficulty 

(Folk, 1960, p. 5-6). Clearly, therefore, the JuniataTuscarora boundary may not be a time line separating Ordovician and Silurian rocks. This point is 

emphasized by Thompson (1970). 

Further confusion regarding the OrdovicianSilurian boundary in eastern Pennsylvania stems 

from Willard and Cleaves' (1939, p. 1185) belief that 

a remnant of the Bald Eagle can be found at Lehigh 

Gap and east into Northampton County. If this were 

true, the basal clastic rocks underlying Blue Mountain in this area could be Maysvillian in age 

(Willard, 1943, P. 1118). We doubt the identification 

of the Bald Eagle at Lehigh Gap. In this report and 

as suggested by Epstein and Epstein (1967, 1969), 

the basal conglomerates at Lehigh Gap are placed in 

the Shawangunk. Except for clast size, we recognize 

no difference between the basal conglomerates and 

the conglomerates in the overlying beds. Thus we do 

not recognize the disconformity that Willard and 

Cleaves ( 1939) postulated, based on the absence of 

the intervening Juniata between the beds they believed to be Bald Eagle and Shawangunk. 

The age of these rocks is further clouded by the 

previously held supposition that unconformities 

mark systemic boundaries. Thus, Willard and 

Cleaves (1939, p. 1165) maintained that the Juniata 

is either Silurian or Ordovician depending on acceptance of one of two proposed hiatuses in eastern 

Pennsylvania as the Ordovician-Silurian boundary. 

Bald Eagle, Juniata, Tuscarora, and Shawangunk 

rocks in central and eastern Pennsylvania are shallow-marine and fluvial clastic rocks derived from 

highlands uplifted to the southeast as the result of 

the Taconic orogeny (for example, Swartz, 1948; 

Thomson, 1957; Folk, 1960; Yeakel, 1962; Horowitz, 

1966; Epstein and Epstein, 1967, 1969; Smith, 

1967a). The environment of deposition interpreted 

for these rocks is in sharp contrast with the deepwater origin suggested for most of the Martinsburg 

(McBride, 1962). Because the Taconic orogeny may 

have been more or less synchronous in central and 

eastern Pennsylvania, the detritus that makes up the 

Juniata and Bald Eagle in central Pennsylvania 

could be partly of the same age as the Shawangunk 

in eastern Pennsylvania, even though "layer cake" 

interpretations suggest that the Juniata and Bald 

Eagle are older. 

The Shawangunk Formation is sparsely fossiliferous. No fossils have been found in the Weiders or 

Minsi Members except for Arthrophycus, 40 feet 

above the base of the Minsi at Lehigh Gap and also 

in a large block of rock in the retaining wall about 

300 feet south of the Martinsburg-Shawangunk contact along U.S. Interstate 80 in Delaware Water Gap. 

Schuchert (1916, p. 546) reported Arthrophycus 225 

feet above the base of the Shawangunk (Minsi Member of this report) in Delaware Water Gap. 

In the overlying interbedded shales, siltstones, and 

sandstones (Clinton Formation of Swartz and 

Swartz, 1931; quartzite-argillite unit of Epstein and 

Epstein, 1967, 1969; Clinton Member of Epstein, 

1970, 1971; Lizard Creek Member of this report), 

the only fossils reported are rare specimens 

of Arthrophycus (Schuchert, 1916), eurypterids 

(Clarke and Ruedemann, 1912), Dipleurozoa (Johnson and Fox, 1968), and Lingula (Epstein and Epstein, 1969). Lingula, a long-ranging facies fossil, 

and dipleurozoans, very rare as fossils, cannot be 

used for correlation. 

Arthrophycus alleghaniense, in the ShawangunkTuscarora of Pennsylvania, New Jersey, and New 

York, was believed to be a guide fossil for the Lower 

Silurian (Medinan) by Schuchert (1916), Willard 

(1928), and Swartz and Swartz (1930). Arthrophycus has been regarded as a fossil worm or plant remains (Becker and Donn, 1952) but is now generally 

recognized as a feeding burrow (Hantzschel, 1962), 

a conclusion reached long ago by Sarle (1906). However, according to Seilacher (1955), these ichnofossils generally have no age significance but only paleoecological significance. Amsden (1955), Pelletier 

(1958), and Yeakel (1962) showed that Arthrophycus was strongly facies controlled, apparently limited to transitional fluvial and marine environments. 
16 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

It is obvious, therefore, that Artkrophycus is a facies 

fossil and cannot be used to date the Shawangunk. 

Eurypterid remains found in the Shawangunk 

Formation at Otisville, N.Y., and Delaware Water 

Gap, Pa., and in the Tuscarora Sandstone at Swatara 

Gap, Pa. (Clarke and Ruedemann, 1912; Swartz and 

Swartz, 1930, 1931) have been considered to be 

Early Silurian in age. Swartz and Swartz (1930, 

p. 473), however, sounded a note of caution, "It 

would seem inevitable to conclude that the Shawangunk is early Silurian unless the eurypterids are 

without significance for correlation." Grabau ( 1913) 

gave arguments for the fact that eurypterids were 

river-dwelling organisms, have long stratigraphic 

ranges, and do not form "exact horizon markers" 

(p. 526). Clarke and Ruedemann (1912) were likewise a bit cautious, indicating that the age assignment at Delaware Water Gap was tentative because 

(1) the eurypterids were altered and fragmented, 

(2) the evolution of eurypterids may have been slow 

and the complete ranges of species unknown, and 

(3) eurypterids are apparently facies controlled. 

Both Amsden (1955) and St~rmer (195·5) emphasized the scarcity and environmental control of 

eurypterids. Apparently, eurypterids were confined 

to brackish and fresh waters, which agrees with the 

environmental interpretation of the Shawangunk as 

a fluvial-transitional marine sequence. (See section 

"Depositional Environments and Paleogeography.") 

Thus, neither the eurypterids in the Shawangunk 

Formation and Tuscarora Sandstone, nor Arthrophycus, can be used for precise age determination 

because of facies control and uncertainty of species 

ranges. It is interesting, in this regard, that Willard 

(1928, p. 257) compared the Shawangunk eurypterids with those found in the Pittsford Shale (Upper Silurian) and Frankfort Shale (Upper Ordovician, Edenian) of New York. He found the closest 

faunal similarity with the Frankfort and concluded 

that the Shawangunk must be Early Silurian in age 

because "the presence of Arthrophycus in the Shawangunk points to its being Lower Silurian, since 

that organism is conceded to be of that age." 

In summary, the evidence used to date the Shawangunk Formation of eastern Pennsylvania has been 

based on insecure stratigraphic data and fossils that 

are strongly environmentally controlled and whose 

ranges are poorly known because of rare occurrences. The evidence needs reevaluation. It is conceivable that the Shawangunk is Late Ordovician in 

age as well as Early Silurian; the same conclusion 

was also reached by Berry and Boucot ( 1970, p. 

224). Perhaps intensive investigations of the phytoplankton assemblages, such as the one made by 

Cramer (1969) for the Rose Hill and Tuscarora 

Formations of central Pennsylvania, can provide 

the information needed to accurately date these clastic rocks. 

DEPOSITIONAL ENVIRONMENTS AND 


PALEOGEOGRAPHY 


Regional stratigraphic relations, sedimentary 

structures, and petrographic characteristics suggest 

that rocks of the Shawangunk Formation are a 

clastic ·wedge of material shed from a linear highland source uplifted during the Taconic orogeny to 

the southeast and deposited by rapidly flowing 

streams (Weiders, Minsi, Tammany Members) and 

in a transitional marine-continental environment 

(Lizard Creek Member) (fig. 22). Incomplete data 

indicate that the source rocks were chiefly sedimentary and low-grade metamorphic types, shot through 

with quartz veins. 

The major environments of deposition that we 

previously interpreted for Silurian clastic rocks in 

eastern Pennsylvania (Epstein and Epstein, 1967, 

1969) are in general agreement with those of Smith 

(1967a, b) and Smith and Saunders (1970), who 

made an independent study of these rocks from New 

York to central Pennsylvania. 

In general, previous workers on the Shawangunk 

have considered it to be predominantly deltaic or 

fluvial in origin (for example, Grabau, 1909, 1913; 

Swartz, 1948; Yeakel, 1962; Hunter, 1970), although 

an exclusively littoral origin (Schuchert, 1916; Willard, 1928) and tidal origin (Clarke and Ruedemann, 

1912) have also been proposed. 

Initially, uplift of the source area was rapid, for 

the basal Shawangunk rocks in the Weiders Member are coarse. These rocks were possibly present 

southeast of the Delaware Water Gap area but were 

removed by erosion. Shallow-marine sediments that 

would have heralded the arrival of the initial fluvial 

sediments presumably overlay the Martinsburg at 

one time but were eroded by the streams that ultimately deposited the basal Weiders and Minsi rocks. 

In general, the sediments are finer grained higher 

in the Shawangunk and to the southwest, representing a transgressive phase and lowering of the 

source area concomitant with basin subsidence. A 

regressive phase, or progradation of fluvial sands 

over marginal marine sediments of the Lizard Creek 

Member, is indicated by the overlapping of the 

coarse-grained rocks of the Tammany Member and 

its southwestward-extending tongues. 
PALEOGEOGRAPHY 17 

Northwest 

. . (). 

• 0 

. () 0 

• () • () 0 

0 • () • 0 • • 

. () . 

0 • 

0 • 0 

C> • () 

. () 

0 

Source rocks 

EXPLANATION 

(See caption for description) 

2 

~I 3 

Alluviated coastal plain Tidal flats Barrier zone 

FIGURE 22.-Generalized block diagram showing sedimentary environments and major lithofacies in the Shawangunk 

Formation. Alluviated coastal plain: 1, Streams of high gradient, coarse load, low sinuosity (braided). A, Bedforms in 

upper flow regime (planar beds, antidunes) and upper lower flow regime (dunes); chiefly conglomerate and sandstone; 

Weiders Member. B, Bedforms in lower upper flow regime (planar beds) and upper lower flow regime (dunes); 

chiefly conglomeratic quartzite and quartzite; Minsi and Tammany Members; tongues of Tammany Member in Lizard 

Creek Member. Tidal flats: 2, Intertidal flats, may include narrow supratidal flats, tidal creeks, estuary, lagoon, beach. 

Shale, siltstone, sandstone, minor nodules of collophane, siderite, and chlorite. Irregularly bedded and laminated, 

graded, rippled, flaser-bedded, cut-and-fill, ball-and-pillow structure, burrowed, restricted fauna. Lizard Creek Member. 

Barrier zone: 3, Offshore bar and beach. Conglomerate, sandstone, and siltstone. Foreshore laminations, crossbedding, 

scouring, wave-tossed shell debris, textural maturity. Lizard Creek Member. 

The Weiders Member is characterized by abrupt 

alternations of conglomerate beds, medium- to very 

coarse grained sandstone, and very minor argillite. 

The conglomerates contain quartz pebbles as much 

as 6 inches long and are indistinctly bedded to 

planar bedded. The sandstones are planar bedded to 

crossbedded, indicative of relatively rapid flow (upper lower flow regime to upper flow regime; Simons 

and Richardson, 1962.; Fahnestock and Haushild, 

1962; Gwinn, 1964), and are probably channel and 

bar deposits of streams. One possible antidune was 

recognized at Lehigh Gap (Epstein and Epstein, 

1969, fig. 50). Grain size is variable, and pebbles 

are well rounded to subangular, indicative of a fluviatile environn1ent (Sames, 1966). The conglomerates are partly polymictic, and the sandstones are 

generally poorly sorted and submature to immature 

with a muscovite- and chlorite-rich matrix (graywackes and protoquartzites are most common). Paleocurrent trends in the W eiders, as well as in all 

units considered to be fluvial, are unidirectional to 

the northwest (fig. 23), as first recognized by Yeakel 

(1962), who supported a fluviatile environment for 

the Shawangunk. 

The bedforms and sedimentary structures indicate 

deposition by streams that had great competency 

and steep gradients. The abrupt superposition of 

beds with varied grain size, internal structure, and 
18 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

N N 

40 40 

30 

1­

"M~~ z 1­ trend, w z u w ~42°W. c::: u w c::: a.. wQ.. 

n=18 n=60

A B 

FIGURE 23.-Histograms showing current trends from crossbedding in the Shawangunk Formation at Lehigh Gap (A) 

and Delaware Water Gap (B). Beds rotated to horizontal. 

thickness (fig. 3) suggests erratic fluctuations in current flow and channel depth. These features are characteristic of braided streams. The characteristics of 

modern braided streams, similar to those described 

above, have been discussed in many papers (for 

example, Leopold and Wolman, 1957; Doeglas, 1962; 

Allen, 1965; Coleman, 1969). Smith (1970) compared characteristics of the Shawangunk with the 

braided South Platte-Platte River in Colorado and 

Nebraska. Scour and fill is common, and, in general, 

basal channel surfaces have a relief no greater than 

5 feet, indicating that the streams flowed in constantly shifting anastomosing channels. The nearly 

complete absence of fine siltstone and shale in the 

Weiders is also characteristic of braided stream deposits. Braided streams shift so rapidly across the 

fluvial plain that they are able to remove most finegrained sediment. The few thin pelites present are 

mere relicts of these finer deposits. Some of the mud 

and silt was incorporated in the coarser sediment as 

flattened mud balls. 

Glaciofluvial deposits of Pleistocene age in eastern 

Pennsylvania are very similar to the conglomerates 

and sandstones in the Weiders. (See Epstein, 1969.) 

The glacial sediments were undoubtedly deposited 

by braided streams with high velocity and coarse 

load. Fahnestock ( 1963) described similar deposits 

of the White River, Mount Rainier, Wash. 

The Minsi Member, which overlies the Weiders 

at Lehigh Gap and forms the basal unit of the 

Shawangunk Formation at Delaware Water Gap 

(fig. 2), is similar to the Weiders except that peb­
PALEOGEOGRAPHY 19 

bles are smaller (less than 2 inches long) and argillites, probably representing overbank and backwater 

deposits, are more abundant. Mud c,racks in at least 

one siltstone bed (fig. 8) show that these deposits 

were subject to subaerial exposure. Numerous sedimentary units are superposed as in the Weiders 

Member, and here also represent deposition by 

braided streams. The finer grain size, however, suggests that the source highlands were lowered or 

eroded back at this time. 

The coarse clastic rocks of the Minsi Member 

grade abruptly up into interbedded sandstone, siltstone, and shale of the Lizard Creek Member which 

is interpreted to indicate that the Minsi alluviated 

coastal plain merged into broad flats in a complex 

transitional continental-marine environment (fig. 

22). The following subenvironments were probably 

represented: Tidal flat, barrier bar or beach, estuary, 

tidal channel and gully, lagoon, and shallow subtidal. 

In addition, other complex environm~nts characteristic of deltas described by many workers, for example, Shepard and Lankford, 1959; Coleman and 

Gagliano, 1965; Bernard and LeBlanc, 1965; Donaldson, 1966, were probably also represented, but more 

detailed studies are needed for their differentiation. 

Both currents and waves shaped the sedimentary 

structures on tidal flats, so irregularly bedded, laminated, and lenticular sandstone, siltstone, and shale 

are abundant. (For recent examples, see Hantzschel, 

FIGURE 24.- Flaf:er bedding (ripple lensing) showing oblique 

bedding in rippled Eandstone lenses surrounded by shale 

laminae, Lizard Creek Member of the Shawangunk Formation, roadcut along State Route 45, Carbon County, Pa. 

This structure is typical of the tidal-fiat environment (compare with Reineck, 1967, fig. 9). Negative print of acetate 

peel from measured section 3, unit 66. 

1939; Straaten, 1955, 1961; Evans, 1965; Reineck, 

1967.) Flaser bedding (ripple lensing, figs. 11, 24), 

scour-and-fill structure, minute load-cast structures, 

and crossbedding are common and are analogous to 

features in modern sediments reworked by tidal currents ( Hantzschel, 1939), especially in tidal channels 

(Straaten, 1955), or are due to rippled sand deposited between beds of mud in deeper subtidal 

areas during storms (H. E. Reineck, oral commun., 

1968). The Lizard Creek also contains mud flasers, 

formed by settling of mud in troughs of ripples in 

sand beds during slack water at the turn of the tide. 

These are similar to structures found in recent tidal 

channels (Reineck and Singh, 1967) and are characteristic of tidal-flat sediments. Load casts are 

found at the bases of many sandstones. Laminated 

shales to fine sandstones, locally common in the Lizard Creek, probably represent sediment deposited 

from suspension under tranquil water conditionsat periods of slack tide or in protected bodies of 

water, such as lagoons (McKee, 1957). Some of the 

laminated beds are red and may have been deposited 

on high tidal flats and partly bound by algae, as described in The Wash (England) by Evans (1965). 

Similarly, red burrow-mottled siltstones may have 

formed as supratidal deposits in the oxidizing zone 

above mean-tide level; these would be landward 

equivalents of intertidal green beds (McKee, 1957; 

Nichols, 1962). 

Tidal-flat sediments may be reworked considerably (burrow mottled) by organisms, so burrows are 

common (figs. 15, 16). The animals that were responsible for the burrows have not generally been 

preserved as fossils. Similar lack of preservation has 

been noted on recent tidal flats in the Netherlands 

(Straaten, 1955) and has been attributed to decay 

by bacteria, scavenging by other organisms, and 

lack of hard parts (organisms probably worms). 

The few fossils that have been found are consistent 

with the interpretation of a tidal-flat environment: 

linguloid brachiopods (see following discussion), 

Arthrophyc-us, eurypterids, and Dipleurozoa (see 

section on age of the Shawangunk). 

Some crossbedded sandstones, many having pronounced truncated bases, contain flattened mud 

clasts or mud galls; these sandstones may be tidalchannel or tidal-gully deposits. (See Straaten, 1961). 

The clasts were de·rived either from reworked curled 

mud cracks or from slumped mud banks undercut by 

the tidal creeks. The latter cause was probably the 

more important one, because mud cracks were not 

seen in the Lizard Creek. The presence of the mud 

clasts indicates that the mud that made up the banks 
20 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

was very cohesive. Many of the sandstones at Lehigh 

Gap grade up into flaser-bedded and laminated siltstone, fine sandstone, and shale, and are probably 

fining-upward deposits of meandering tidal creeks. 

These intervals are generally a few feet thick. Some 

of these beds grade up into red bioturbated shaly 

siltstone that may represent sediments oxidized and 

organically reworked above mean high tide. Similar 

cycles of high- and low-tidal-flat sediments were described by Smith (1968) at Schuylkill Gap. 

Some thicker crossbedded sandstone, as much as 

8 feet thick, containing mud clasts, may be fluviatile 

sediments that prograded onto the flats or may be 

estuarine sediments, that is, sands that were carried 

into the transitional environment under the influence 

of currents generated by streams. The distinction 

between tidal-channel estuarine and fluviatile sands 

may be difficult to make because the sedimentary 

features are similar in the two (Land and Hoyt, 

1966). The lateral change in facies between the Tammany Member (believed to be fluviatile) and the 

Lizard Creek Member, as well as the gradation between the fluviatile beds of the Minsi Member and 

the Lizard Creek, supports the interpretation that 

some of the beds in the Lizard Creek are estuarine. 

Clean red sandstones may have been deposited in an 

agitated and well-oxygenated estuarine environment, 

perhaps near streams that carried colloidal iron to 

be deposited as a cement. 

Many sandstones in the Lizard Creek appear 

evenly textured and massive in outcrop, but on polished or wet sawed surfaces they are finely bedded 

to laminated (fig. 10). These mature calcareous sandstones (generally orthoquartzites, fig. 14) contain 

heavy minerals concentrated in laminae and have 

primary current lineation. They are interpreted as 

beach or bar deposits associated with the tidal flats. 

If our interpretation is correct, the paleogeography 

may have been similar to the chenier plains along 

the southern coast of Louisiana. (See Hoyt, 1969.) 

These marginal delta plains are downdrift from active delta progradation. Sediments are carried into 

this area by longshore currents from areas of stream 

debouchment. Beach ridges (cheniers) form by the 

sorting action of waves on the mudflats during periods of slack sedimentation. Shifting streams may 

then bring more sediment into the area, so that the 

flats prograde. The sediments are then reworked 

during a decrease in sedimentation, and another 

beach ridge forms. Thus, the chenier plain develops 

with alternations of beach-ridge sands and mud-flat 

silts and clays. 

Other sandstones in the Lizard Creek Member are 

ripple topped (fig. 13) and are similar to the sandflat sandstones described by Evans (1965). Rare 

silty sandstones have ball-and-pillow structure, due 

to soft-rock slumping (fig. 12), that were possibly 

produced during storms. Ore (1964), however, described similar intraformational deformation in deposits of braided streams and attributed them to 

movement of saturated sediment, a condition also 

prevalent on tidal flats. 

Collophane (calcium fluorapatite), siderite, and 

chlorite nodules found at Lehigh Gap and collophane 

nodules at Delaware Water Gap (fig. 2) are unique 

to the Lizard Creek. The thin rim of chlorite on 

some siderite nodules, the flattening of some nodules 

over clastic grains, the protrusion of quartz grains 

from the nodules into the surrounding matrix, the 

presence of coarser quartz grains and broken brachiopod shells in the nodular beds, and other soft-rock 

features (fig. 18) indicate that the nodules formed 

as early diagenetic replacements in an agitated environment and that transport of the nodules was 

slight. Shell fragments of linguloid brachiopods, 

probably Lingula, suggest that these nodules formed 

in shallow warm waters, possibly brackish, at depths 

probably less than 60 feet (Craig, 1952). Thompson 

( 1968) noted linguloid brachiopods in silty clays and 

sands in troughs or swales between sandbars in the 

lower intertidal zone of the Colorado River delta. 

Thus, finding Lingula reworked in beach sands (fig. 

18) is not unusual. 

If some of the chlorite in the Lizard Creek was 

originally chamosite (found in equivalent rocks in 

States adjacent to Pennsylvania), as mentioned previously, this would have important environmental 

3ignificance. Porrenga (1967a, b) has shown that 

chamosite is presently found in tropical waters at 

depths generally less than 60 meters and temperatures greater than 20°C, whereas glauconite forms 

in deeper and colder waters. Hunter ( 1960, 1970) 

showed a northeast-trending belt of chamosite, succeeded by a glauconite belt to the northwest, in the 

Appalachian basin in Clinton time. The association 

of siderite with chamosite is considered by Hunter 

to indicate deposition in quiet waters that were 

deeper than the agitated, oxygenated waters closer 

to shore, in which hematite was deposited. It has 

been suggested that siderite forms beneath the 

water-sediment interface in a reducing environment 

with restricted water circulation (Curtis and Spears, 

1968) and that siderite and chlorite are diagenetic 

products of the reaction between limonite, quartz, 

and organic reducing material (Bubenicek, 1969). 
PALEOGEOGRAPHY 21 

These conditions may be satisfied in lagoons (Sheldon, 1964) and estuaries. 

Collophane nodules are associated with the chlorite 

and siderite nodules and with shell fragments of 

Lingula. Formation of these associated nodules, all 

of apparently very early diagenetic or penecontemporaneous origin, requires a unique set of physical, 

chemical, and biological conditions. The collophane 

appears to have formed as concretionary masses or 

by precipitation of carbonate fluorapatite from sea 

water (the presumably authigenic nodules at Delaware Water Gap are dominantly carbonate fluorapatite and contain lesser amounts of muscovite and 

quartz, as indicated by X-ray diffraction analysis) 

and as replacements of siltstone and shale (as seen 

in thin sections of rocks from Lehigh Gap). Lingula 

may have been the main intrabasin source for the 

phosphate, but the ultimate source was either dissolved phosphorous carried in by streams or brought 

into the shallow nearshore waters by downwelling 

currents from farther offshore (Gulbrandsen, 1969). 

The phosphate was tied up in and concentrated by 

organisms such as Lingula and eurypterids. Under 

favorable conditions the phosphate was concentrated 

into nodules upon death of the animals. Solution and 

reprecipitation of the phosphatic shell material at or 

just below the water-sediment interface probably 

produced phosphatized silt and mud locally (Clarke, 

1924). Many of the phosphate nodules have the 

same soft-rock deformation features that were described for siderite nodules. Occasionally, waves 

and tidal currents churned these muds and also 

comminuted some of the phosphatic shell material. 

Many of the Lingula-nodule beds are heavy lag concentrates in well-sorted sandstones having laminations typical of foreshore beach deposits (fig. 18A). 

There can be little doubt that the phosphate nodules 

are of very shallow water origin. (See Bushinski, 

1964, and references cited therein.) The interpretation that parts of the Lizard Creek Member are 

estuarine in origin is in harmony with the conclusion of Pevear (1966) that phosphatization probably 

occurred in estuaries of the Atlantic Coastal Plain. 

The Tammany Member is very similar to rocks 

in the Minsi Member and indicates progradation of 

fluviatile sediments (or a deltaic topset plain) out 

over the transitional environment of the Lizard 

Creek (fig. 2). The progradation shows that the 

amount of material entering the basin exceeded the 

removal capacity of ocean waves and currents. This 

localized regression may have been caused by the 

shifting of the locus of major stream debouchment 

458-355 0 - 72 - 4 

rather than by uplift in the source area, because the 

coarse deposits of the Tammany die out southwest 

of Delaware Water Gap. 

The occurrence of ferroan dolomite beds and dolomite and calcite nodules in the Tammany Member 

(fig. 21) indicates proximity to a body of salt water 

that supplied magnesium for dolomitization, possibly 

in the same manner described for the penecontempOraneous dolomitization of limestone in supratidal environments. (For example, see Shinn and others, 

1965.) Implied in this scheme are brines in the 

ground water, evaporation exceeding rainfall so that 

water reaching the surface by capillary action is enriched in salts, magnesium-to-calcium ratio increasing by precipitation of gypsum, and dolomitization 

of calcareous shales by the magnesium-rich waters. 

The water body close by may have been the sea, a 

lagoon, or a lake on the alluviated coastal plain. 

Fluvial conditions persisted into Bloomsburg time, 

but the fining-upward cycles and higher content of 

siltstone and shale in the Bloomsburg indicate that 

the braided streams of the Tammany gave way to 

meandering streams as the southeastern source area 

was progressively lowered by erosion. For a discussion of the Bloomsburg Red Beds see Epstein and 

Epstein ( 1969) and Epstein ( 1971). 

The long linear outcrop belt of the Weiders and 

Minsi Members suggests that these lower coarse 

clastic sediments of the Shawangunk Formation 

were deposited on a coastal plain of alluviation with 

a linear source to the southeast (fig. 22). Yeakel 

(1962) noted loci of thicker deposition for Tuscarora 

and "equivalent beds" in the Delaware Water Gap 

area and farther southwest in the Harrisonburg 

area, Virginia and West Virginia. However, at Delaware Water Gap his reported thickness included the 

Lizard Creek and Tammany Members, whereas, at 

Lehigh Gap, where his reported thickness is onefourth as much, he included only the Weiders and 

Minsi Members of this report. 

The large pebbles in the W eiders Member (more 

than 6 inches long in places) suggest that the Fall 

Line could not have been far to the southeast, perhaps in the area of the Reading Prong. (See Yeakel, 

1962.) Abundant pelitic fragments in basal conglomerates argues against long-distance transport of 

these clasts. The maturity of the pebbles (quartz, 

chert, sandstone, and quartzite) and of the nonopaque heavy minerals (preponderantly zircon and 

tourmaline, many grains of which are rounded) suggests a sedimentary source. Biotite, fragments of 

metaquartzites (composite grains of stretched 
22 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

quartz), and rare grains of slate, as well as 

abundant sand-sized grains of detrital muscovite, 

indicate that the source rocks were partly made up 

of low-grade metamorphic rocks. The source area 

also had abundant quartz veins, because most of the 

pebbles are vein quartz with an irregular mosaic of 

interlocking quartz crystals; many contain inclusions of vermicular chlorite. 

Basal beds in the Minsi Member contain enough 

potash feldspar (fig. 7) to suggest that the source 

was also partly composed of granitic or gneissic 

rocks. It might be argued that granitic and gneissic 

rocks were major components of the source area and 

that the mineralogical maturity of sandstones and 

conglomerates of the Shawangunk is due to deep 

weathering in the source area. Facts against this 

view are ( 1) the well-rounded condition of many 

zircon and tourmaline grains, indicating multicycle 

transport, (2) the presence of some feldspar in the 

Minsi Member at Delaware Water Gap, showing 

that weathering was insufficient to remove it, (3) 

the absence of kaolinite in the clay-size fraction (as 

shown b~ X-ray diffraction studies), which indicates 

that weathering was not intense enough to produce 

kaolinite from feldspar (however, any kaolinite that 

may have been present could have converted to muscovite by diagenesis or by metamorphism following 

deep burial), and ( 4) the large size of the pebbles, 

which indicates short transport, bold valleys in the 

supposed deeply weathered source area to supply the 

pebbles and exposure of fresh bedrock in the valley 

walls. Less stable minerals, such as feldspar, amphibole, and pyroxene, which would have been deposited with the quartz-bearing conglomerates and 

sandstones, should be abundantly present, but they 

are not. The absence of feldspar, amphibole, and 

pyroxene in most Shawangunk rocks apparently cannot be attributed to stream abrasion, for Russell 

(1937) has shown that these minerals persist in the 

Mississippi River and are only slightly diminished 

after transport of more than 1,000 miles. 

Perhaps, mature sediments cannot be derived 

from active erosion of youthful mountains in humid 

tropical areas, even though the rate of chemical 

weathering is high. For example, in Papua, New 

Guinea, Ruxton ( 1970) noted that fluvial sediments 

are derived mostly from rapid erosion of steep mountain slopes, where only weakly weathered soils are 

developed. The source rocks are metamorphic, mafic, 

and ultramafic. Rock fragments and unstable mineral grains are common in the alluvium, even though 

soils on the interfluves contain abundant kaolin and 

quartz. Studies in other areas, such as the Andes 

(Gibbs, 1967) and the mountains of Venezuela (Van 

Andel and Postma, 1954) and Dominica (Elliot, 

1951), show that physical weathering dominates 

chemical weathering in active orogenic mountain 

areas, and extensive maturation of the eroded mineral suite is not to be expected. Physical weathering 

was also probably favored during Silurian time because of the lack of extensive protective vegetation 

cover, if indeed any was present at all. 

The absence of limestone pebbles and the presence 

of chert supposedly derived from cherty limestones 

is difficult to explain. Possibly the chert was derived 

from bedded (radiolarian?) chert generally associated with marine pelites and graywacke. This possibility is favored by the presence of siliceous slate 

fragments in the basal part of Weiders Member at 

Lehigh Gap. The composition of Shawangunk conglomerates and sandstones, thus, does not seem to be 

compelling evidence for a deeply weathered source 

area. Not necessarily contrary to this view is Hunter's (1970) conclusion that iron in the rocks of 

the Clinton Group and its equivalents was derived 

from weathering of iron-bearing rocks in the source 

area. He noted that the fluvial environment was one 

in which iron was transported but not deposited in 

any great quantity. This is in accord with the sparsity of fine-grained sediments in the fluvial sediments 

of the Weiders, Minsi, and Tammany Members. The 

iron was precipitated when the streams debouched 

into the nearshore marine environment. Hunter 

maintained that the degree of weathering increased 

as the source area was lowered by erosion and that, 

for this reason, feldspar, chert, and polycrystalline 

quartz, which are selectively separated from singlecrystal quartz during increased weathering, are less 

abundant higher in the section. On the basis of this 

supposition, then, the Weiders and Minsi represent 

intense erosion and little weathering in the source 

area, and the Lizard Creek Member, with its red beds 

and abundant iron-rich minerals, indicates more intense weathering. This hypothesis would be most 

attractive were it not for the fact that the Tammany 

Member, which is similar to the Minsi Member and 

thicker than the Minsi at Delaware Water Gap, 

grades laterally into the Lizard Creek. 

If the higher iron concentrations were due to 

greater chemical weathering in the source rocks 

and if the nature of the source rocks remained unchanged, the red beds should contain less unstable 

or semistable minerals than the nonred beds. However, the thickest red-bed sequence in the area, the 

Bloomsburg Red Beds, is petrographically distinctive 

from the underlying Shawangunk rocks in that felds­
MEASURED SECTIONS 23 

par and chlorite, and to a lesser extent biotite, are 

abundant. Therefore, we conclude that the mineralogy of the source rocks, and not the degree of chemical weathering, controlled the mineralogy of clastic 

Silurian rocks in eastern Pennsylvania. The probability that the climate was warm and arid at least 

during Bloomsburg time, is supported by the occurrence of correlative thick salt deposits in New York 

(Rickard, 1969). Lotze (1964) included the Silurian 

rocks of Pennsylvania in the worldwide belt of 

evaporites of Silurian time, concluding that the area 

was extremely warm and arid. Schmalz (1969, 1971) 

argued that evaporite deposition does not require 

an arid climate, but only one in which evaporation 

exceeds runoff and precipitation. However, he 

(Schmalz, 1969, p. 798) did state that an environment "characterized by a dry and usually hot climate with a high net evaporation rate," is one of 

the basic conditions for the accumulation of geologically significant evaporite sequences. 

Recognition of the precise source area is problematical and open to speculation. Feldspathic and 

quartzose metasedimentary rocks and smaller 

amounts of amphibolite, marble, and granitic rocks 

are now mainly exposed in the Reading Prong 

(Drake, 1969). Conceivably, equivalent rocks that 

may have been exposed during Silurian time could 

have been the source for some of the Shawangunk, 

and chert-bearing carbonates and quartzites of Cambrian and Ordovician age could have supplied other 

components. However, hornblende is extremely rare 

in the Shawangunk, and pyroxene and epidote, all 

common in Prong rocks, were not seen in any thin 

sections of Shawangunk rocks examined. Moreover, 

the Reading Prong characteristically lacks abundant 

quartz veins and is, therefore, not an enticing possibility as a source area for the· Shawangunk. Could 

it be that rocks dissimilar to those now found to the 

southeast were the source for the Shawangunk, emplaced in their position in thrust sheets or nappes 

but long since eroded? Drake (1970) reported that 

a sequence of low-grade metasedimentary and metavolcanic rocks is found on the north border of the 

Prong. These are apparently younger than the more 

highly metamorphosed rocks they overlie and once 

could have been more extensive. They could have 

been a source for much of the Shawangunk. 

The scattered specks of graphite in the Lizard 

Creek Member are unique and indicate a metamorphic source. A possible source area is the Piedmont 

of southeastern Pennsylvania. Here, Miller (1912) 

reported graphite in the Pickering Gneiss and limestones ("Franklin Limestone") of Precambrian age. 

In general, graphite is disseminated in these rocks 

as flakes averaging %6-Ys inch in diameter, about 

the same size found in the Shawangunk. If the Piedmont rocks were the source, the graphite may have 

been transported by flotation in streams and would 

have undergone very little reduction in size. However, the Pickering Gneiss is feldspar rich, and, as 

mentioned, the Shawangunk contains rather small 

quantities of feldspar. 

In summary, judging from the available data, we 

conclude that during Shawangunk time the climate 

was warm and at least semiarid, and that the source 

area had high relief. The mineralogy of the Shawangunk was controlled by the nature of the source 

rocks, which were composed predominantly of sedimentary and low-grade metamorphic rocks with 

abundant quartz veins and small local areas of feldspathic gneisses or granites. Erosion was intense, 

although enough broad interfluves may have been 

present so that a regolith developed that could supply iron to the depositional basin. 

MEASURED SECTIONS 

Section 1 

[Shawangunk Formation along U.S. Interstate 80, Delaware Water Gap, 

Portland quadran~le. Warren Countv, New Jersey. Beds generally dip 

moderately northwest but are interrupted by two small folds. Measure­ ment begms w1thin an estimated 3 ft of the covered contact between the 

Shawangunk Formation and Martinsburg Formation and ends at the con­ tact between the Shawangunk Formation and Bloomsburg Red Beds. Type 

section of the Tammany and Minsi Members of the Shawangunk 

Formation] 

Shawangunk Formation: Thickness

(ft) 

Tammany Member: 

65. Quartzite and quartz-pebble conglomerate, 

medium-gray (N5) to medium-dark-gray 

(N4), limonitic; quartz pebbles as much 

as 1.0 in. long; dark-gray (N3) argillite 

clasts as much as 2.0 in. long; beds as 

much as 12.0 ft thick; crossbedded and 

planar-bedded; uppermost few feet consists of brownish-gray (5YB 5/1) fine- to 

medium-grained quartzite and of conglomeratic quartzite that has angular pebbles 

as much as 1.0 in. in diameter; top of unit 

forms dip slope in contact with red sandstone and siltstone of the Bloomsburg Red 

Beds; basal contact gradational; thickness of unit approximate ______________ 241.0 

64. Quartzite, medium-gray (N5) to mediumdark-gray (N4), fine-grained, hematitic, 

crossbedded; in massive beds as much as 

5.0 ft thick; some interbedded dark-gray 

(N3) argillite ------------------------ 125.0 

63. Argillite, dark-gray (N3) ; thins updip; 

basal contact abrupt ________________ 3.2 

62. Quartzite, medium-gray (N5), fine-grained, 

limonitic, massive; basal contact gradational -------------------------------- 4.8 
24 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

Section 1-Continued 

Shawangunk Formation-Continued 	 Thickness 

(ft)

Tammany Member-Continued 

61. Quartzite and argillite. Medium-gray (N5) 

to medium-dark-gray (N4) fine-grained 

quartzite interbedded with dark-gray 

(N3) argillite. Beds about 3.0 in. thick. 

Unit forms base of steep cliff at an elevation of 660 ft. Dark-gray argillite 

abruptly overlies dense massive quartzite 

at base ------------------------------ 5.8 

60. Quartzite, medium-gray (N5) to mediumdark-gray (N4), fine- to medium-grained, 

limonitic, massive; a few beds of darkgray (N3) argillite; basal contact concealed -------------------------------- 69.1 

59.Covered ------------------------------- 7.0 

58. Quartzite, shaly siltstone, and silty shale. 

Medium-gray (N5) to medium-dark-gray 

(N4), fine- to medium-grained, conglomeratic, limonitic, massive, crossbedded and 

planar-bedded quartzite in beds as much 

as 5 ft thick interbedded with dark-gray 

(N3) lenticular argillite in beds as much 

as 2 ft thick and argillite intraclasts as 

much as 5 in. long. Unit is more conglomeratic towards top. Basal contact abrupt 295.0 

57. Shaly siltstone, dark-gray (N3), laminated; 

thins and pinches out 50 ft updip; basal 

contact abrupt _______________________ 1.5 

56. Quartzite, medium-light-gray (N6) to darkgray (N3) , very fine to very coarse 

grained; quartz pebbles as much as 2.0 in. 

long; crossbedded and planar bedded. 

Scattered beds of dark-gray siltstone and 

scattered siltstone pebbles as much as 3 

in. long. Basal contact abrupt and disconformable ____ _________ _____________ 2.9 

55. Argillite and quartzite. Dark-gray (N3), 

quartzitic, arenaceous, limonitic, laminated shaly siltstone interbedded with medium-gray (N5) fine-grained quartzite. 

Unit thins updip as dark-gray agillite 

pinches out. Basal contact abrupt and disconformable __________________________ 3.5 

54. Quartzite and silty shale. Medium-gray 

(N5) to medium-dark-gray (N4), fineto medium-grained, partly conglomeratic, 

massive, crossbedded and planar-bedded 

quartzite with quartz pebbles as much as 

1h in. long and dark-gray (N3) argillite 

pebbles as much as 2 in. long interbedded 

with dark-gray argillite as much as 6 in. 

thick which thins updip. Pyrite cubes 

scattered throughout. Basal contact 

abrupt ____________________________ _ __ 25.4 

53. Shaly siltstone, dark-gray (N3) with pyrite 

cubes approximately 1 mm long, mediumto coarse-grained, massive, crossbedded 

and planar-bedded; conglomeratic quartzite bed 11 in. thick in middle of unit, 

separated from an overlying fine- to meSection 1-Continued 

Shawangunk Formation-Continued 	 Thickness 

(ft)

Tammany Member-Continued 

dium-grained quartzite 7 in. thick by a 

2-in. siltstone bed. Unit thins updip. Basal 

contact abrupt _______________________ 5.7 

52. Quartzite and argillite. Medium-gray (N5) 

to medium-dark-gray (N4), fine- to 

coarse-grained, conglomeratic (angular to 

rounded quartz pebbles as much as % in. 

long and dark-gray angular to discoidal 

argillite pebbles as much as 3 in. long), 

crossbedded and planar-bedded, massive 

quartzite with lenticular beds of darkgray (N3) shaly siltstone as much as 4 

in. thick. Unit more conglomeratic 

towards top. Basal contact gradationaL_ 14.8 

51. Quartzite, medium-gray (N5) to mediumdark-gray (N4), fine- to medium-grained, 

limonitic, crossbedded and planar-bedded, 

massive; beds average 1.5 ft thick; conglomeratic in uppermost foot; small pyrite cubes scattered throughout unit, especially in upper part; a few dark-gray 

(N3) burrow-mottled shaly siltstone and 

siltstone beds as much as 3 in. thick which 

pinch out within a few tens of feet are 

scattered throughout unit; basal contact 

abrupt ------------------------------ 11.1 

Total 	 thickness of Tammany 

Member ______________________ 815.8 

Lizard Creek Member: 

50. Quartzite, dark- to medium-gray, very fine 

to fine-grained, silty, argillaceous; contains dark-gray discoidal silty shale clasts 

as much as 2 in. long; unevenly bedded; 

basal contact gradational ____ __________ 3.4 

49. Silty shale, dark-gray, alternating with 

medium-gray (N5) fine-grained limonitic 

quartzite in uneven beds less than 1 to 8 

in. thick. Basal dark-gray (N3) argillite 

lying abruptly ·in contact with massive 

quartzite ---------------------------- 5.3 

48. Quartzite, medium-gray (N5), fine-grained, 

with scattered limonite flecks and darkgray (N3) argillite pebbles averaging 

about % in. in length; massive; vaguely 

parallel bedded to structureless; ripples 

with 3-in. wavelengths 1.5 ft below top; 

beds less than 1 to 15 in. thick; a few thin 

interbeds of dark-gray (N3) silty shale; 

basal contact irregular and gradational _ 6.8 

47. Quartzite, shaly siltstone, and silty shale. 

Dark-gray, siliceous, very unevenly bedded and lenticular shaly siltstone and 

silty shale beds as much as 5 ft thick 

with thin lenses and beds of quartzite 

interbedded with medium-gray (N5) to 

dark-gray (N3) fine-grained, massive, 

lenticular, partly crossbedded, locally very 

limonitic (limonite specks as much as 1,4 

in. in diameter) , partly conglomeratic 
MEASURED SECTIONS 25 

Section !-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Lizard Creek Member-Continued 

(intraclasts of dark-gray silty mudstone 

derived from underlying beds range in 

length from less than 1,4 in. to as much 

as 2 in.) quartzite. Quartzite in beds 1-18 

in. thick. Many bedding planes contorted 

and show flow structures, channeling, 

some load casts, flaser bedding, and burrow mottling. Some beds rippled. Basal 

contact consists of dark gray (N3) silty 

mudstone in disconformable contact with 

massive quartzite. Some quartzite beds 

contain phosphatic intraclasts as much 

as 1 in. long. Base of unit has small scattered phosphatic intraclasts __________ 46.9 

46. Quartzite, silty shale, and siltstone. Medium-dark-gray (N4), fine-grained, massive quartzite (with limonite flecks in 

upper half) underlain by medium-gray 

(N5) fine-grained limonitic quartzite unevenly finely to moderately bedded (flaser 

bedding and burrowed where siltstone and 

silty shale are interbedded with finer 

grained quartzite), interbedded with 

dark-gray (N3) muddy siltstone and silty 

mudstone in beds and lenses 1,4-12 in. 

thick (mud flasers). Basal beds lenticular, 

very unevenly bedded, contain black phosphatic nodules. Basal 2 ft consists of very 

irregularly interbedded lenticular quartzite and flaser-bedded shale with abundant phosphatic nodules. Bases of many 

quartzite lenses have load casts and sole 

marks. Phosphatic intraclasts weather 

white; they are rounded to angular and 

as much as 1.5 in. long. Many nodules 

are partly penetrated by quartz sand 

grains. Contact between units 45 and 46 

is at road level at northwest end of stone 

retaining wall and is abrupt __________ 5.5 

45. Silty shale, shaly siltstone, and silty quartzite, medium- (N5) to dark-gray (N3), 

fine-grained, partly limonitic; weather 

pale yellowish orange (10YR 8/6) to 

light brown (5YR 5/6); laminated but 

appear massive in part; partly burrow 

mottled, vertical burrows in upper 6 ft 

of unit; basal contact abrupt ___________ 10.1 

44. Quartzite, medium-dark-gray (N4), finegrained, partly limonitic; weathers light 

gray (N7) ; massive; some beds contain 

dark-gray silty shale clasts as much as 

1 in. long; bedding characteristic-crossbedded and planar bedded; basal contact 

abrupt ------------------------------ 4.4 

43. Shaly siltstone, silty shale, and quartzite. 

Dark-gray (N3) arenaceous shale and 

siltstone interbedded and interlensed with 

thin quartzite in upper half of unit. Lightto medium-gray, partly silty, laminated, 

Section !-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Lizard Creek Member-Continued 

crossbedded, and massive quartzite with a 

few thin beds of dark-gray mudstone in 

beds as much as 5 in. thick make up 

lower half of unit. A 3-in.-thick bed of 

fine-grained convoluted quartzite 2.5 ft 

below top of unit. Convolutions of laminated medium-light-gray (N6) to medium-gray (N5) very fine grained quartzite and medium-dark-gray (N4) siltstone. Basal contact abrupt ___________ _ 7.2 

42. Quartzite and silty shale. Medium-lightgray (N6) to medium-gray (N5), finegrained, massive, crossbedded quartzite 

containing dark-gray (N3) argillite fragments as much as 1 in. long. Quartzites 

are rippled and occur in beds 2-15 in. 

thick and are unevenly interbedded and 

interlaminated with dark-gray shaly siltstone. Unit partly burrow mottled. Silty 

shale makes up 12 percent of unit. Basal 

contact consists of quartzite abruptly 

overlying dark-gray silty shale ________ 6.2 

41. Quartzite and shaly siltstone. Dark-gray 

(N3) laminated shaly siltstone interbedded with dark-gray fine-grained to very 

fine grained silty crossbedded quartzite 

with clasts of siltstone as much as 1h in. 

long. Unit partly burrow mottled at top 

with shale-filled burrows. Unit faulted at 

road level and repeated 50 ft to northwest 

on northwest limb of small anticline. 

Basal contact abrupt _______________ _ 2.3 

40. Quartzite, medium-gray (N5), fine-grained, 

massive; a few intercalations of darkgray (N3) silty shale; crossbedded and 

planar bedded; basal contact abrupt ____ 4.3 

39. Quartzite, light-olive-gray (5Y 5/2) to 

medium-dark-gray (N4), fine-grained, 

crossbedded and planar-bedded; silty 

above basal foot and very limonitic 

towards top of unit; basal foot consists 

of medium-gray (N5) quartzite resting 

disconformably on dark-gray (N3) shaly 

siltstone and silty shale of unit 38. Quartzite-filled limonitic burrows in upper half 

(approx 1,4 in. in diameter and as much 

as 10 in. long) occur in silty fine-grained 

quartzite. Very conspicuous vertical burrows in upper 7 ft. Overlying units folded 

and faulted. Contact between units 39 and 

40 is abrupt and is repeated 50 ft to 

northwest ---------------------------­ 9.2 

38. Shaly siltstone and shale, dark-gray (N3), 

laminated, alternating with light-olivegray (5Y 5/2) and medium-gray (N5) 

fine-grained limonitic crossbedded quartzite that contains thin beds of dark-gray 

shale and clasts as much as 1 in. long; 

beds from less than 1h to 12 in. thick. 
26 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

Section 1-Continued Section 1-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Lizard Creek Member-Continued 

Upper 3ft consists predominantly of laminated dark-gray argillite. Basal contact 

abrupt ------------------------------- 8.1 

37. Quartzite, medium-gray (N5), fine-grained, 

limonitic, crossbedded; a few thin intercalations of dark-gray (N3) silty shale 

constitute about 5 percent of unit; beds 

4-20 in. thick; basal contact abrupt and 

disconformable ______________________ _ 5.9 

36. Silty shale and shaly siltstone, dark-gray 

(N3), in uneven laminae and beds (beds 

as much as 3 in. thick), interbedded with 

light-olive-gray (5Y 5/2), fine-grained, 

limonitic, thin-bedded quartzite which 

constitutes about 15 percent of unit. 

Many sand-filled burrows parallel to bedding. Basal contact abrupt and disconformable ---------------------------- 7.4 

35. Quartzite, moderate-brown (5YR 3/4) and 

medium-gray (N5), fine-grained, very 

limonitic (with limonite concretions as 

much as 1 in. in diameter) , unevenly 

bedded; bedding plane 1 ft above base 

has ripple marks with amplitude of about 

lf2 in. and wavelength of about 3.5 in.; 

basal contact abrupt and disconformable 1.5 

34. Shaly siltstone and silty shale, dark-gray 

(N3) ; contain spherical limonitic concretions averaging about 1 in. in diammeter; unevenly interbedded with lightolive-gray (5Y 5/2) to medium-gray 

(N5) fine-grained, limonitic, thin-bedded 

quartzite containing dark-gray (N3) 

argillite pebbles as much as 1 in. long. 

Upper %, ft is a light-gray (N7) finegrained quartzite with dark-gray argillite 

pebbles as much as 1 in. long. Basal contact is abrupt and undulatory with many 

limonite concretions at or near the contact --------------------------------­ 7.1 

33. Silty shale, shaly siltstone, and quartzite. 

Siltstone contains some clay clasts 1,4, in. 

in diameter and is partly burrow mottled. 

Medium-gray (N5) to medium-lightgray (N6) fine-grained limonitic crossbedded even-bedded quartzite makes up 

50 percent of unit and is interbedded with 

dark-gray (N3) partly silty shale. A 3­

in.-thick laterally discontinuous quartzite 

bed, 4 ft above base of unit, contains thin 

(0.1-114 in.) branching argillite-filled 

burrows about 1 in. long. The finer 

grained quartzites are ripple topped. Ripples have wavelengths of 3 in _______ _ 8.7 

32. Quartzite, medium-gray (N5), fine-grained; 

limonite flecks; massive; crossbedded; 

laminated; basal contact abrupt and disconformable ------------------------­ 5.8 

31. Quartzite, medium-gray (N5) to mediumShawangunk Formation-Continued Thickness 

(ft) 

Lizard Creek Member-Continued 

light-gray (N6), fine- to medium-grained, 

limonitic, massive, partly rippled; contains minor shale clasts as much as 1 in. 

long; in beds 4 in. to 2.5 ft thick, alternating with dark-gray (N3) silty shale, 

p~rtly burrowed, in beds 1 in. to 1 ft 

thick. Basal contact abrupt ____________ 13.6 

30. Siltstone, shaly, dark-gray (N3), with fine 

sand-filled burrows and fine-sand lenses; 

basal contact abrupt ______ ____________ 1.3 

29. Quartzite, medium-gray (N5), fine-grained, 

crossbedded, with 1h -in.-long clay galls; 

alternating with dark-gray (N3), limonitic silty shale and shaly siltstone in beds 

as much as 2 in. thick which constitutes 

less than 20 percent of unit. Basal contact abrupt and consists of a 2-ft quartzite abruptly overlying dark-gray argillite 7.6 

28. Quartzite, medium-gray (N5), fine-grained, 

crossbedded, unevenly bedded, with rare 

clay galls as much as 1 in. long; constitutes 70 percent of unit; alternating with 

dark-gray (N3) burrow-mottled silty 

shale and shaly siltstone. Basal contact 

gradational __________________________ 7.0 

27. Quartzite, medium-gray (N5), fine- to 

medium-grained, limonitic, crossbedded, 

massive; basal contact abrupt and disconformable ____________ ______________ 5.8 

26. Quartzite, medium-dark-gray (N4), finegrained, thin-bedded to laminated, crossbedded, alternating with dark-gray (N3) 

silty shale and shaly siltstone; beds lh-3 

in. thick. Basal contact abrupt __________ 4.0 

25. Quartzite and muddy siltstone to silty mudstone. Medium-dark-gray (N4), limonitic 

(limonite flecks about 0.1 in. in diameter 

scattered throughout), massive, unevenly 

bedded quartzite; contains scattered darkgray (N3) argillite clasts as much as 2 

in. long; in beds 1-11 in. thick; constitutes more than 90 percent of unit. Thin 

beds of dark-gray partly burrow-mottled 

shaly siltstone. Graphite grains as much 

as 0.1 in. long scattered throughout _____ 3.8 

24. Quartzite and silty claystone. Light-olivegray (5Y 5/2), fine-grained, laminated, 

partly limonitic, evenly bedded, crossbedded quartzite alternating with darkgray (N3), silty, slabby, burrow-mottled shale, which constitutes about 65 percent of unit. Beds 1-8 in. thick. Basal 

contact gradational ___________________ 4.8 

23. Quartzite and shaly siltstone. Medium-lightgray (N6), medium- to fine-grained, limonitic, crossbedded quartzite with scattered 

dark-gray (N3) argillite clasts as much 

as 1 in. long; in beds 1-19 in. thick; 
________________ 

MEASURED SECTIONS 27 

Section !-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Lizard Creek Member-Continued 

makes up about 60 percent of unit. 

Quartzites interbedded with medium-darkgray to dark-gray shaly siltstone and 

minor amounts of silty shale. Unit unevenly laminated to evenly bedded. Widely 

scattered irregular grains of graphite as 

much as 0.1 in. long. Some fine to medium 

sand fills burrows 14 in. in diameter. 

Basal contact covered ________________ _ 16.0 

22. Quartzite and shaly siltstone interbedded, 

in beds 1 in. to 3 ft. thick. Covered at road 

level but exposed in gully above _______ _ 30.0 

21. Covered. 	Probably consists mostly of siltstone and shale ______________________ _ 23.0 

Total thickness of Lizard Creek 

Member 273.0 

Minsi Member : 

20. Quartzite, light- (N7) to medium-gray 

(N5), medium-grained to conglomeratic; 

has quartz pebbles as much as 1h in. long; 

massive; crossbedded and planar bedded; 

uppermost bed is massive conglomerate 

about 2 ft thick and is exposed in culvert 

on east side of road; 1 in.-thick mediumgreenish-gray (5G 5/1) siltstone 5.3 ft 

above base. Basal contact gradational __ _ 12.8 

19. Siltstone, shaly, dark-gray (N3), finely laminated, interbedded with medium-darkgray (N4), conglomeratic, silty, finegrained quartzite. Basal contact abrupt _ 1.5 

18. Quartzite, medium-gray (N5), fine- to 

medium-grained, limonitic; scattered angular quartz and chert pebbles as much as 

1h in. long; crossbedded and planar 

bedded; massive; a few interbedded darkgray (N3) shaly siltstone beds 1 in. thick 

or less; basal contact abrupt and disconformable ---~---------------------- 11.5 

17. Siltstone and silty shale, dark-gray (N3), 

compose about 65 percent of unit; interbedded with medium-gray (N5), mediumgrained, crossbedded quartzite and quartzand chert-pebble conglomerate. Basal contact abrupt -------------------------- 3.7 

16. Quartzite, light-olive-gray (5Y 5/2) to 

light-gray (N5), medium- grained, partly 

conglomeratic (angular to subrounded 

quartz pebbles as much as 1h in. long and 

shale clasts as much as 1 in. long) ; local 

ripples; lenticular; dark-gray (N3) laminated shaly siltstone in beds 1-8 in. thick 

composes about 10 percent of unit. Basal 

contact abrupt _______________________ 37.8 

15. Siltstone, shaly, dark-gray (N3), interbedded with light-olive-gray (5Y 5/2) and 

medium-dark-gray (N4), medium-grained, 

limonitic, crossbedded quartzite. Unit 

from top to bottom consists of: 

Siltstone ---------------- 0.8 

Section !-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Minsi Member-Continued 

Quartzite _______________ 5.3 

Siltstone 2.2 

Basal contact abrupt and disconformable 8.3 

14. Conglomerate and quartzite. Light-olivegray (5Y 5/2) to medium-dark-gray 

(N4) conglomerate with clasts as much 

as %, in. long composed predominantly of 

quartz; also scattered dark-gray (N3) 

shale pebbles as much as 1 in. long; conglomerate alternates with medium-gray 

(N5) to dark-gray (N3) medium- to 

coarse-grained quartzite. Unit massively 

bedded and crossbedded. Basal 1h ft is 

a conglomerate bed which locally grades 

into underlying light-gray (N7) quartzite 24.3 

13. Quartzite, light-gray (N7) to light-olivegray (5Y 5/2), fine- to medium-grained, 

planar-bedded; weathers to a lighter color 

than units above and below; few thin 

lenses of darker gray quartzite; basal 

contact gradational ___________________ 8.0 

12. Quartzite, conglomeratic quartzite, and conglomerate, light-olive-gray (5Y 5/2) and 

medium-dark-gray (N4) to light-gray 

(N7), predominantly medium grained, 

massively bedded, crossbedded and finely 

laminated; a few intercalations of darkgray (N3) shaly siltstone totaling no 

more than 3 in.; some siltstone pebbles 

as much as 4 in. long. Basal contact 

abrupt ------------------------------- 89.0 

11. Siltstone, shaly, arenaceous, dark-gray 

(N3), siliceous, laminated, alternating 

with light-olive-gray (5Y 5/2) and medium-dark-gray (N4) medium- to coarsegrained partly conglomeratic (pebbles no 

more than 14 in. long) quartzite. Basal 

contact abrupt and disconformable ___ _ 4.8 

10. Quartzite and conglomerate, light-olivegray (5Y 5/2) and medium-dark-gray 

(N4), fine- to medium-grained, massively 

bedded, crossbedded; a few thin intercalations and channel fillings of dark-gray 

(N3) siltstone constitute about 4 percent 

of unit; conglomerate constitutes about 

10 percent of unit. Basal contact abrupt 

and disconformable __________________ _ 31.8 

9. Conglomerate and quartzite, light-olivegray (5Y 5/2) to medium-dark-gray 

(N4), crossbedded and planar-bedded; 

quartzitic conglomerate has clasts as 

much as %, in. in diameter and scattered 

silty shale clasts as much as 4 in. long; 

conglomerate is interbedded with darkgray (N3) fine-grained argillaceous 

quartzite and siltstone. At road level are 

four dark-gray siltstone beds which are 

as much as 1 ft thick; these beds thicken 

and thin laterally. Conglomerates and 
28 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

Section 1-Continued 

Shawangunk Formation-Continued Thickness 

(ft)

Minsi Member-Continued 

quartzites between the siltstones are lenticular. This unit is persistent for at least 

100 ft updip. Mud cracks found updip at 

edge of cliff, approximately 60 ft above 

road level. Basal contact abrupt and disconformable ___________________________ 7.2 

8. Quartzite, alternating medium-gray (N5) 

and light-olive-gray (5Y 5/2) to lightgray (N7), fine- to medium-grained; 

planar-bedded beds 2 in. to 3 ft thick; 

basal contact gradational ____________ 4.7 

7. Conglomerate and conglomeratic quartzite, 

light-olive-gray (5Y 5/2) to mediumdark-gray (N4), crossbedded and planarbedded; clasts as much as 1 in. long in a 

matrix of mediurn-grained quartzite; 

form basal 2.5 ft and grade up into medium-gray medium-grained laminated to 

fine-bedded quartzite. Basal contact 

abrupt ------------------------------- 6.0 

6. Quartzite, light-olive-gray (5Y 5/2.), fineto mediurn-grained; a few scattered pebbles about :14 in. long; basal few feet contains lenses of medium-dark-gray (N4) 

medium- to coarse-grained quartzite; upper half of unit crossbedded; basal half 

of unit planar bedded; basal contact 

abrupt ------------------------------ 9.5 

5. Quartzite, light-olive-gray (5Y 5/2), medium-gray (N5) to medium-dark-gray 

(N4), predominantly medium grained, 

partly coarse grained; a few scattered 

angular pebbles as much as 1h in. long; 

crossbedded; basal contact abrupt ______ 8.2 

4. Conglomerate and quartzite, light-olivegray (5Y 5/2) and light-gray (N7) to 

medium-gray (N5), medium- to coarsegrained, limonitic, partly crossbedded, 

lenticular; pebbles of angular quartz and 

dark-gray (N3) chert as much as 2 in. 

in diameter and averaging 1h in. in diameter. Base of many conglomerate beds disconformable, with channels about lh ft 

deep. There are six pronounced conformable contacts within this unit at road 

level. Conglomerate grades up into or is 

interbedded with finer quartzite. Conglomerate beds 1 in. to 1 ft thick. A few 

light-olive-gray (5Y 5/2) shaly siltstone 

lenses averaging about 2 in. in length 

scattered throughout unit. Basal contact 

abrupt ------------------------------- 11.3 

3. Quartzite and conglomeratic quartzite. 

Angular pebbles of milky quartz predominate in a matrix of medium-dark-gray 

(N4) medium- to coarse-grained quartzite; matrix also contains scattered darkgray (N3) chert and argillite pebbles as 

much as 1 in. long. Unit is conglomeratic 

Section 1-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Minsi Member-Continued 

and feldspathic at base becoming finer 

grained toward top. Unit is unevenly bedded; conglomeratic beds lenticular. Basal 

contact gradational ___________________ 1.8 

2. Quartzite, light-olive-gray (5Y 5/2) and 

medium-light-gray (N6) to medium-gray 

(N5), fine-grained to conglomeratic; 

crossbedded to planar bedded; partly 

limonitic; angular to rounded quartz pebbles with a few dark-gray (N3) to 

grayish-black (N2) chert pebbles approximately 1h in. long; irregular bedded and 

crossbedded; conglomeratic, medium- to 

coarse-grained, and fine-grained quartzite 

beds 1 in. to 1 ft thick alternate; thin 

lenses of light-olive-gray (5Y 5/2) shaly 

siltstone not more than 1 in. thick and 

as much as 10 ft long; limonitic concretions, 1-llh in. in diameter are scattered 

throughout but occur in zones along bedding planes; basal contact covered ____ 18.4 

1. Covered; contact between Shawangunk and 

Martinsburg Formations covered by colluvium; covered interval about 2 ft thick 2.0 

Approximate thickness of Minsi 

Member ________________________ 302.6 

Total thickness of Shawangunk Formation ________________________ 1,391.2 

Section 2 

[Part of the Shawangunk Formation exposed in roadcut on southwest side of Pa. Rte. 115 in Wind Gap in Blue Mountain at Wind Gap, Wind Gap 

quadrangle, Northampton County, Pa. Beds near vertical] 

Shawangunk Formation (part): Thickness 

(ft) 

Lizard Creek Member (part): 

41. Quartzite and argillite, partly exposed and 

weathered; quartzite predominates. Unit 

light olive gray (5Y 6/1), medium dark 

gray (N4), and medium gray (N5); 

weathers grayish orange (10YR 7/4) to 

dark yellowish orange (lOYR 6/6). 

Quartzite, very fine to medium-grained, 

burrowed. Uppermost 23 ft exposed on 

shoulder 10 ft above road and contains 

several beds, as much as 3 ft thick, of 

interlaminated argillite and quartzite. Top 

of unit 550 ft south of intersection of 

Pa. Rte. 115 and old Pa. Rte. 115. Upper 

contact concealed; basal contact abrupt__ 31.0 

40. Quartzite and argillite. Medium-dark-gray 

(N4) to medium-light-gray (N6), very 

fine to medium-grained, irregularly bedded (flaser bedded) quartzite; beds 1-3 

in. thick. Dark-gray (N3) argillite; occurs as clasts and fine streaks in the 

quartzite and as beds as much as 7 in. 

thick; argillite has many sand-filled burrows. Unit partly covered; basal contact 

abrupt ------------------------------- 23.0 
MEASURED SECTIONS 29 

Section 2-Continued 

Shawangunk Formation (part)-Continued Thickness 

(ft) 

Lizard Creek Member (part)-Continued 

39. Quartzite, dark-gray (N3) to mediumdark-gray (N4), fine-grained; numerous 

flecks of limonite; one massive bed; basal 

contact abrupt _______________________ 1.0 

38. Quartzite and argillite, like unit 40. Quartzite in beds from 1 to 6 in. thick. Argillite 

in beds as much as 3 in. thick; also as 

flattened clasts and as thin lenses as much 

as several inches long. Unit partly burrowed and irregularly flaser bedded. 

Basal contact gradational ____________ 4.6 

37. Quartzite, medium-dark-gray (N4) to medium-light-gray (N6), very fine to coarsegrained; minor amounts of medium-lightgray (N6) -weathering argillite; beds 

massive and as much as 1ft thick. Lower 

2 ft consists of interlaminated argillite 

and quartzite. Unit crossbedded near base. 

Basal contact abrupt ________________ 8.1 

36. Quartzite and argillite, in equal amounts, 

interlaminated and interbedded. Darkgray (N3) argillite; laminae uneven and 

wavy with scattered quartzite-filled burrows which range from parallel to perpendicular to bedding. Light-olive-gray 

(5Y 6/1) to dark-gray (N3), fine-grained 

quartzite; beds 2-6 in. thick. Basal con­ tact abrupt __________________________ 8.3 

35. Quartzite, light-gray (N7) to medium-darkgray (N4), fine- to coarse-grained, limonitic; generally massively bedded; contains some laminae; beds 2 in. to 1.5 ft 

thick; some beds with scattered dark-gray 

(N3) flattened argillite clasts as much as 

1 in. long and irregular laminae; beds 

0.5 in. thick to laminae of light-olive-gray 

(5Y 6/1) medium-grained quartzite are 

interbedded with dark-gray argillite 14 

in. above base of unit. Lower 14 in. of 

unit contains a 0.5-ft-thick zone with 

vertical burrows more than 1 in. deep and 

14 in. in diameter. Minor amounts of 

dark-gray (N3) argillite and mediumgray (N5) very fine grained quartzite 

form 3 ft of upper part of unit. Basal 

contact abrupt _______________________ 11.7 

34. Argillite, dark-gray (N3). Unit contains 

two beds, 0.75 in. thick, of light-gray 

(N7) medium-grained quartzite; unit 

pinches out updip; basal contact abrupt_ 0.9 

33. Quartzite, medium-dark-gray (N4) to very 

light gray (N8), fine- to medium-grained, 

massively bedded; beds 1-14 in. thick. 

Argillite-filled burrows, 14 in. in diameter, 

scattered in quartzite. Argillite clasts as 

much as 1 in. long occur in a few quartzite beds. Interbedded coarse-grained 

quartzite and dark-gray (N3) argillite in 

Section 2-Continued 

Shawangunk Formation (part)-Continued Thickness 

(ft) 

Lizard Creek Member (part)-Continued 

beds 1-3 in. thick make up about 1 ft of 

unit. Basal contact abrupt ____________ 14.7 

32. Argillite, dark-gray (N3); basal contact 

abrupt ------------------------------ 0.8 

31. Quartzite, medium-gray (N5), fine- to medium-grained, massive; abundant limonite 

specks approximately 1 mm in diameter; 

basal contact abrupt _________________ 3.1 

30. Quartzite, light-gray (N7), fine- to coarsegrained; numerous dark-gray (N3) argillite clasts as much as 0.5 in. long, averaging about 0.5 mm thick and flattened p·arallel to bedding; cross bedded; basal contact channeled and abrupt ____________ 0.9 

29. Quartzite and argillite, interbedded and interlaminated, containing mud flasers. 

Argillite, dark-gray (N3). Quartzite, 

medium-gray (N5), fine-grained. Basal 

contact abrupt ----------------------- 1.5 

28. Quartzite, medium-dark-gray (N4), medium-grained; massive bed; basal contact 

abrupt ------------------------------- 1. 7 

27. Quartzite and argillite, interbedded. Argillite, medium-dark-gray (N4) to mediumgray (N5). Quartzite, medium-gray (N5) 

to medium-dark-gray (N4), fine-grained. 

Beds 1-4 in. thick; basal contact abrupt 1.2 

26. Quartzite, medium-dark-gray (N4) to lightgray (N7), medium- to coarse-grained, 

laminated to massive; contains rounded 

and flat argillite intraclasts 14-2 in. long; 

most beds 1 in. to. 2.5 ft thick and together with thin beds (less than 1 in.) of 

dark-gray (N3) argillite they make up 

about 5 in. of unit; unit partly crossbedded and flaser bedded; basal contact 

abrupt ------------------------------- 8.3 

25. Sandstone, medium-gray (N5), very fine 

to fine-grained, micaceous; weathers light 

olive gray (5Y 6/1); unevenly laminated; 

a 6 in. dark-gray (N3) argillite at top 

of unit; partly burrow mottled; basal 

contact abrupt ----------------------- 3.3 

24. Quartzite, medium-gray (N5), mediumgrained, limonitic; beds as much as 2 ft 

thick; some dark-gray (N3) argillite 

clasts a few inches long; basal contact 

abrupt ------------------------------- 7.0 

23. Quartzite, medium-dark-gray (N4), medium- to coarse-grained; laminated; basal 

contact abrupt _______________________ 0.6 

22. Quartzite, like unit 24 but without argillite 

clasts; basal contact abrupt __________ 9.5 

21. Argillite and quartzite. Argillite, dark-gray 

(N3) to medium-dark-gray (N4). Quartzite, medium-gray (N5) to medium-light 

gray (N6), very fine to fine-grained. Beds 

as much as 8 in. thick. Basal contact 

abrupt ----------------------.,-------- 3.1 
30 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

Section 2-Continued 

Shawangunk Formation (part)-Continued Thickness 

(ft) 

Lizard Creek Member (part)-Continued 

20. Quartzite, medium-light-gray (N6), medium-grained, limonitic, massive and laminated; basal contact abrupt __________ 2.0 

19. Argillite and quartzite. Dark-gray (N3) to 

medium-dark-gray (N4) argillite; beds 

as much as 6 in. thick. Medium-gray (N5) 

and very light gray (N8), fine-grained, 

indistinctly laminated quartzite; beds 

averaging about 2 in. thick. Contact between beds sharp; basal contact abrupt 2.5 

18. Quartzite, medium-gray (N5) to mediumlight-gray (N6), fine- to coarse-grained, 

limonitic; massive beds as much as 1 ft 

thick; unevenly bedded; partly crossbedded and laminated; a few mediumdark-gray (N4) argillite clasts, 1-2 in. 

long, occur in the quartzite; basal contact abrupt __________________________ 7.2 

17. Argillite and quartzite. Argillite, dark-gray 

(N3) to medium-gray (N5), laminated, 

and quartzite, dark-gray (N3) to lightgray (N7), fine- to medium-grained, 

limonitic, laminated, with some cross laminations, to massive; in beds as much as 

4 in. thick. Unit partly covered. Basal 

contact abrupt __ _____________________ 6.2 

16. Sandstone, light-gray (N7), fine-grained, 

quartzose, slightly limonitic; argillaceous 

at base; indistinctly laminated; basal 

contact abrupt _______________________ 0.7 

15. Quartzite and argillite. Medium-gray (N5) 

to medium-dark-gray (N4), medium- to 

coarse-grained quartzite; beds as much as 

1ft thick. Medium-gray (N5) to mediumdark-gray (N4) argillite. Beds of darkgray (N3) argillite with low-angle crossbedding; beds of unit as much as 1.5 ft 

thick; basal contact abrupt __________ 9.5 

Incomplete thickness of Lizard Creek 

Member _______________________ 172.4 

Minsi Member: 

14. Quartzite, medium-light-gray, mediumgrained; weathers light brown (5YR 

5/5); limonitic; crossbedded and indistinctly laminated; basal contact abrupt__ 3.6 

13. Quartzite and argillite. Dark-gray (N3) to 

medium-dark-gray (N4) quartzite; very 

fine to fine-grained; argillaceous and 

pyritiferous; irregularly laminated; lowangle trough crossbedding. 8 ft from base, 

a 1-ft-thick medium-grained, limonitic 

quartzite occurs. Medium-dark-gray (N4) 

to dark-gray (N5) argillite makes up 20 

percent of unit. Basal contact gradational 11.1 

12. Quartzite, medium-light-gray (N6), fineto medium-grained; weathers grayish 

orange (lOYR 7/4) to light brown (5YR 

5/6); a few irregular laminae of meSection 2-Continued 

Shawangunk Formation (part)-Continued Thickness 

(ft) 

Minsi Member-Continued 

dium-dark-gray argillite; basal contact 

abrupt ------------------------------- 1.4 

11. Argillite, dark-gray (N3), containing medium-gray (N5) fine-grained sandstone 

laminae; basal contact abrupt ________ 0.8 

10. Quartzite, medium-gray (N5), very coarse 

to medium-grained, conglomeratic, containing pebbles as much as ~ in. long; 

massively bedded; beds as much as 3.5 ft 

thick; thin beds (1-2 in. thick) of darkgray (N3) to medium-dark-gray (N4) 

argillite. Argillite clasts, as much as 5 

in. long scattered in quartzite beds. Unit 

crossbedded and laminated; some beds 

contain pyrite euhedra. Basal contact 

abrupt and forms base of channel ____ 13.7 

9. Argillite and quartzite, interbedded and interlaminated. Dark-gray (N3) argillite; 

stained on joint surfaces to light brown 

(5YR 5/6). Light-gray (N7), finegrained, argillaceous quartzite; ripple 

bedded; beds from laminae to 1.5 ft thick. 

Basal contact abrupt ___ _______________ 2.0 

8. Quartzite, medium-light-gray (N6), medium-grained to very coarse grained, containing pebbles as much as ~ in. long; 

weathers grayish orange (lOYR 7/6); 

scattered light-brown (5YR 5/6) limonite 

specks, 1-2 mm in diameter; basal contact 

abrupt ______________ ________________ 3.0 

7. Argillite and quartzite, like unit 9; cross 

laminated to laminated; basal contact 

abrupt------------------------------- 2.8 

6. Quartzite, argillite, and conglomerate; 

chiefly quartzite. Very light gray (N8) to 

medium-dark-gray (N4) quartzite; some 

beds dark gray (N3) and moderate greenish gray (5GY 5/1); predominantly medium grained, but ranges from fine to 

coarse grained, conglomeratic, locally containing pebbles as much as 1,4 in. long; 

beds 4 in. to 4.5 ft thick, averaging 1.5 ft 

thick. Medium-dark-gray (N4) to darkgray (N3) argillite; occurs as thin beds 

and as flat clasts as much as 2 in. long; 

beds 0.25 to 4.5 in. thick, averaging about 

1 in. thick. Conglomerate occurs as thin 

beds 0.5-6 in. thick, averaging about 3 in. 

thick; pebbles mostly white quartz, but 

some are chert. Unit limonitic, crossbedded, and unevenly bedded to laminated. 

Sand-filled burrows 0.5 in. wide occur in 

a 1-in.-thick dark-gray argillite 96.3 ft 

above base of unit. Conglomerate forms 

about 2 ft of unit and argillite about 2.5 

ft. Basal contact abrupt ______________ 136.0 

5. Argillite and sandstone; argillite predominates. Dark-gray (N3) argillite; 

weathers medium gray (N5) to medium 
MEASURED SECTIONS 31 

Section 2-Continued 

Shawangunk Formation (part)-Continued Thickness 

(ft) 

Minsi Member-Continued 

dark gray (N4). Medium-gray (N5), 

medium- to coarse-grained sandstone; 

thin beds (1 em thick) scattered throughout unit. Unit partly concealed. Basal 

contact abrupt _______________________ 3.3 

4. Quartzite, medium-dark-gray (N4), fine- to 

medium-grained, and very light gray 

(N8) to medium-gray (N5), medium- to 

coarse-grained quartzite with pebbles as 

much as % in. long; limonitic; slightly 

crossbedded; crossbed sets about 3 in. 

thick; basal contact and base of unit concealed ------------------------------- 12.0 

3. Quartzite, dark-gray (N3) and pale-reddish-brown (lOR 5/4), medium- to coarsegrained, limonitic, conglomeratic, containing quartz pebbles as much as 1,4 in. 

long; dark-gray (N3) to grayish-black 

(N2) argillite clasts as much as 1.5 in. 

long, averaging less than 1,4 in. thick, lie 

parallel to bedding; argillite also occurs 

as laminae (less than 0.5 mm thick). 

Unit laminated and crossbedded; basal 

contact abrupt ________________________ 1.6 

2. Quartzite, medium-light-gray (N6), containing some light-brownish-gray (5YR 

6/1) beds, medium- to coarse-grained 

with some thin (10 em) very coarse 

grained beds; weathers grayish orange 

( 10 Y R 7I 4) to dark yellowish orange 

(10 YR 6/6); limonitic. Basal foot of unit 

conglomeratic, containing pebbles as 

much as % in. long, averaging about 1,4 

in. long. Unit unevenly bedded and massive; beds 4 in. to 1 ft thick; basal contact abrupt __________________________ 4.5 

1. Covered. 	 Contact of Martinsburg and 

Shawangunk Formations at base of covered unit; bedrock covered by drift of 

pre-Wi~consin age _____________ _______ 25.0 

Total thickness of Minsi Member __ 220.8 

Incomplete thickness of Shawangunk 

Formation _____________________ 393.2 

Section 3 

[Shawangunk Formation and part of the Bloomsburg Red Beds and Martins­ burg Formation exposed along abandoned Lehigh and New England Railroad grade and Pa. Rte. 145, Lehigh Gap, Palmerton quadrangle, 

Northampton County, Pa. Type section of the Weiders and Lizard Creek Members of the Shawangunk Formation. Beds dip moderately to steeply northwest except in a structural terrace 1,000 fEet south of Aquashicola 

Creek] 

Bloomsburg Red Beds (part) : 	 Thickness 

(ft) 

95. Siltstone and shale, grayish-red (5R 4/2) 

to dark-reddish brown (lOR 3/4). Uppermost beds exposed on railroad cut behind 

second north house at northeast corner. 

Section covered at least to Delaware 

Section 3-Continued 

Bloomsburg Red Beds Thickness (part)-Continued (ft) 

Ave., Palmerton, where older outwash 

overlies red float; basal contact concealed ------------------------------- 17.0 

94. Covered. Float same lithic type as unit 95 22.0 

93. Shaly siltstone to fine-grained sandstone, 

grayish-red (5R 4/2) and greenish-gray 

(5GY 6/1) ___________________________ 18.0 

92. Covered. Float same lithic type as unit 9L_ 57.0 

91. Like unit 87 ex~ept for four beds of grayish-red-purple (5RP 4/2) very coarse to 

medium-grained, crossbedded and planarbedded quartzite that has quartz grains as 

much as 1,4 in. long and contains flattened 

dark-reddish-brown (lOR 3/4) silty shale 

intraclasts as much as 3 in. long. These 

beds are 1-2.6 ft thick and are 103, 156, 

182, and 189 ft above base of unit. Scattered sandstone dikes about 2 in. long 

and 1,4 in. thick extend across siltstones 

and shales connecting sandstone beds; 

basal contact abrupt ________________ 419.0 

90. Quartzite, grayish-red-purple (5RP 4/2), 

fine- to coarse-grained; conspicuous bed; 

basal contact abrupt __________________ 3.2 

89. Like unit 87; basal contact abrupt ______ 117.0 

88. Shaly siltstone to very fine grained sandstone, greenish-gray (5GY 6/1) and palered-purple (5RP 6/2) to grayish-redpurple (5RP 4/2), laminated to mottled; 

color changes vertically and laterally; 

basal contact gradational ____________ 3.2 

87. Sandstone, siltstone, and silty shale, in fining-upward cycles. Sandstones at base of 

cycle are generally red purple (5RP 5/2), 

very fine to medium grained (some beds 

are coarse to very coarse grained and a 

few contain quartz pebbles as much as 1,4 

in. in diameter) , and planar bedded to 

crossbedded and may contain flattened 

siltstone or shale intraclasts as much as 

3 in. in diameter. Sandstone beds are 0.3­

5.6 ft thick, and the basal 1-2 in. of each 

bed is medium gray (N5). The base of the 

sandstones is generally abrupt and fills 

channels in the underlying siltstone or 

shale, but some sandstones have a gradational base. The upper contaCt of some 

basal sandstone beds is abrupt, but this 

contact may have been accentuated by 

bedding slippage. The basal sandstones 

grade up into grayish-red (5R 4/2) horizontally laminated and cross laminated 

partly mud-cracked and burrow-mottled 

very fine grained sandstone to siltstone 

with scattered irregular dark-yellowishorange (lOYR 6/6)-weathering ferroan 

dolomite concretions. Pale-green (5G 

7/2) to greenish-gray (5GY 6/1) reduction spots are numerous. These beds gradually grade up into grayish-red (5R 4/2) 
32 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

Section 3-Continued 

Bloomsburg Red Beds (part)-Continued Thickness 

(ft) . 

to dark-reddish-brown (lOR 3/4) mudcracked and burrow-mottled sandy siltstone and silty shale that contain more 

abundant ferroan dolomite concretions. 

The concretions may occur as irregular 

vertical tubes about Vz in. thick and as 

much as 8 in. long that have spread out 

along bedding lamina by apparently replacing the host rock. The very fine 

grained sandstone, siltstone, and shale 

overlying the basal sandstone are 0.3­

7.9 ft thick. Individual fining-upward 

cycles are 0.5-13.3 ft thick. Basal contact 

gradational __________________________ 79.6 

86. Shale, siltstone, and sandstone. Laminated 

greenish-gray (5GY 6/1) and dark-greenish-gray (5GY 4/1) silty shale to finegrained sandstone with as much as 2 ft 

of grayish-red-purple (5RP 5/2) shaly 

siltstone to very fine grained sandstone 

interlaminations and thin lenses in middle 

of unit. Color changes rapidly from red 

to green within 50 ft above road level; a 

few interbedded light-greenish-gray 

(5GY 7/1), fine- to medium-grained, 

chloritic quartzites as much as 1.5 ft 

thick; quartzites have very low angle 

crossbedding and horizontal laminations. 

Minor flaser bedding associated with 

laminae. Some intraclasts and convoluted 

bedding in laminated beds (very small 

scale convolutions). Basal contact abrupt 22.4 

85. Shale, siltstone, and sandstone. Grayishred (5R 4/2) shaly siltstone and silty 

shale from laminae to beds as much as 5 

ft thick; mottled green locally; 1.5-ft.­

thick red shaly siltstone bed in middle of 

unit mud cracked; basal 6-in. bed of red 

and green, very fine to fine-grained, laminated (with small-scale crossbedding) 

sandstone. Basal contact gradational __ 13.4 

84. Sandstone and shaly siltstone; predominantly laminated, containing burrow mottles (burrows are as much as Vz in. wide 

and depress underlying laminae). Greenish-gray (5GY 6/1) very fine grained 

sandstone and dark-greenish-gray ( 5G 

4/1) shaly siltstone and a few grayish-red 

(5R 4/2) siltstone and very fine grained 

sandstone laminae; laminae are gra~ed. 

Basal contact gradational _______ _____ 1.5 

83. Sandstone and siltstone. Predominantly grayish-red (5R 4/2) locally mottled lightgreenish-gray (5GY 7/1), containing 

small light-greenish-gray reduction spots, 

shaly siltstone with thin beds (approx 

6 in. thick) of red-purple (5RP 5/2) very 

fine grained sandstone; 1-ft-thick greenish-gray (5GY 6/1) siltstone in middle of 

unit grades up into grayish-red siltstone; 

Section 3-Continued 

Bloomsburg Red Beds (part)-Continued Thickness 

(ft) 

uppermost foot consists of interlaminated 

very fine to fine-grained sandstone grading up into shaly siltstone. Color changes 

toward top of this laminated sequence 

without regard to lithic type __________ 28.4 

82. Sandstone and siltstone. Greenish-gray (5GY 

6/1), very fine grained sandstone is predominantly well laminated and has smallscale crossbedding (flaser bedding); it is 

irregularly interlaminated with darkgreenish-gray (5GY 4/1) shaly siltstone; 

some burrow mottling. Basal contact 

gradational __ ________________ ________ 5.1 

81. Siltstone and shale. Red-purple (5RP 5/1) 

irregularly laminated to burrow-mottled 

shaly siltstone and silty shale with scattered greenish-gray (5GY 6/1) mottles 

and laminae; 3-foot interval with mud 

cracks in middle of unit; uppermost two 

beds, 9 and 10 in. thick, grade from very 

fine grained sandstone to shaly siltstone; 

small Vz-in. diameter ferroan dolomite 

concretions near top of unit. Basal con­ tact abrupt __________________________ 9.3 

80. Shaly siltstone, medium-greenish-gray 

(5GY 5/1), interlaminated with lightgreenish-gray (5GY . 7 /1) very fine 

grained quartzite. Quartzite occurs as discontinuous lenses and laminae; silty shale 

and quartzite grade up into greenishgray (5GY 6/1) silty shale which grades 

up into light-bluish-gray ( 5B 7/1) pyritic 

siltstone to very fine grained sandstone. 

Within the basal 10 in. of unit, which is 

well laminated to flaser bedded, is an intraclast bed containing convoluted intraclasts; disrupted bedding is due to flowage of clay and very fine sand; sand separated by pinching and swelling into discoidal lumps as much as 2 in. long and 

Vz in. thick (sedimentary boudinage). 

Some sand has complex flowage folds in 

the enclosing clay rnatrix. A few of the 

sand lumps are nearly completely surrounded by clay laminae. Basal contact 

abrupt ------------------------------- 3.7 

79. Quartzite, siltstone, and shale. Mediumlight-gray (N6) to medium-bluish-gray 

( 5B 6/1) fine-grained quartzite in beds 

2 in. to as much as 2 ft thick interbedded 

with medium-dark-gray (N4) to mediumgray (N5) shale in beds 0.5 to as much as 

3 in. thick; shale makes up 15 percent of 

unit; shale contains irregular interlaminations of siltstone and very fine grained 

sandstone. Some beds crossbedded and 

contain shale fragments as much as 2 in. 

long. Basal bed is a light-greenish-gray 

(5GY 7/1) sandy siltstone, 1.7 ft thick; 

basal contact gradational -------------- 14.5 
MEASURED SECTIONS 33 

Section 3-Continued 

Bloomsburg Red Beds Thickness (part)-Continued (ft) 

78. Siltstone and sandstone. Mottled grayishred-purple (5RP 4/2) siltstone and shaly 

siltstone to very fine grained sandstone; 

some samples contain scattered greenishgray (5GY 6/1) mottles; color appears to 

be independent of grain size. Also laminated greenish-gray (5GY 6/1) and grayish-red-purple (5RP 4/2) shaly siltstone. 

Unit is unevenly bedded; beds 1 in. to as 

much as 4.5 ft thick. Unit is color mottled 

and burrow mottled. Basal contact gradational ------------------------------- 22.0 

77. Siltstone and quartzite. Regularly to irregularly interlaminated greenish-gray (5GY 

6/1) and pale-brown (5YR 5/2) shaly 

siltstone containing a few burrow mottles 

interbedded with medium-greenish-gray 

(5GY 5/1) fine-grained quartzite; quartzite makes up approximately 1 ft of unit; 

beds from 4 in. to as much as 2 ft thick; 

bedding is horizontally laminated to very 

low .angle small-scale crossbedding and 

flaser bedding. Basal contact gradational 11.5 

76. Siltstone and sandstone. Mottled (color mottled and burrow mottled) pale-red-purple 

(5RP 6/2) to dusky-red-purple (5RP 

3/2) to pale-red (5R 6/2) and greenishgray (5GY 6/1) siltstone and very fine 

grained sandstone; unevenly bedded; 

beds 3 in. to as much as 3.5 ft thick; one 

3.5-ft bed in middle of unit is greenishgray (bedding vaguely discernible in hand 

sample); basal contact placed at base of 

first red bed; basal bed is lithically similar to beds in unit below _______________ 30.8 

Incomplete thickness of Bloomsburg 

Red Beds ______________________ 898.6 

Shawangunk Formation: 

Lizard Creek Member: 

75. Shale, siltstone, and quartzite. Partly burrow mottled, medium-dark-gray (N4) 

shaly siltstone interlaminated with lightolive-gray, fine-grained quartzite in beds 

as much as 4 ft thick makes up about 87 

percent of unit. Dark-greenish-gray (5GY 

4/1) silty shale interlaminated with siltstone lenses ( flaser bedded) and partly 

burrow mottled in beds as much as 6 in. 

thick makes up about 3 percent of unit. 

Greenish-gray (5GY 6/1), medium-darkgray (N4) to light-gray (N7), and bluishgray (5B 6/1), very fine to coarsegrained, partly laminated quartzite in beds 

4 in. to as much as 1 ft thick makes up 

about 10 percent of unit. Unit contains 

1-in.-thick quartzite bed with nodules of 

siderite and collophane. Basal contact 

abrupt ------------------------------ 38.0 

74. Quartzite and shale. Very light gray (N8) 

to light-gray (N7), medium-grained to 

Section 3-Continued 

Thickness Shawangunk Formation-Continued (ft) 

Lizard Creek Member-Continued 

very coarse grained quartzite in beds 4 in. 

to as much as 4.5 ft thick; some beds contain pebbles as much as 0.5 in. long. 

Medium-dark-gray (N4) shale with discontinuous siltstone laminae in beds less 

than 1,4 in. to as much as 2.2 ft thick. 

Some beds crossbedded. Basal contact 

.abrupt ------------------------------- 22.9 

73. Shale and quartzite. Medium-dark-gray 

(N4) and light-olive-gray (5Y 6/1) shale 

in beds less than 1 in. to as much as 6 ft 

thick makes up 75 percent of unit; some 

beds of shale are silty and regularly interlaminated to mottled with siltstone and 

very fine grained quartzite (flaser 

bedded). Medium-gray (N5) to light-gray 

(N7), very fine to medium-grained qua~tz

ite in beds 1 in. to as much as 4 ft thick 

makes up 25 percent of unit; some beds 

are coarse grained and contain intraclasts 

as much as 2 in. long. Intraclast-nodule 

beds (siderite-chlorite) are thin and scattered in unit. Some beds crossbedded. 

Basal contact abrupt ------------------ 52.4 

72. Shale and quartzite. Medium-dark-gray 

(N4) to light-olive-gray (5Y 6/1) partly 

burrow mottled shale in beds less than 1,4 

in. to as much as 3 in. thick makes up 90 

percent of unit and is interbedded with 

medium-light-gray (N6), medium-gray 

(N5), to medium-greenish-gray (5GY 

5/1) siltstone to fine-grained quartzite in 

beds and lenses that range from laminae 

to as much as 6 in. in thickness and that 

contain small-scale scour-and-fill. Some 

quartzite contains scattered intraclasts of 

medium-dark-gray (N4) phosphatic siltstone as much as 1.5 in. long and is evenly 

bedded to lenticular; these intraclasts or 

nodules are flattened, ovoid, and irregular. 

Unit is partly flaser bedded. Just above 

base of unit is a 5-in.-thick nodule bed 

having a predominantly shale to finegrained-sandstone matrix. Phosphatic siltstone to fine-grained-sandstone nodules 

are as much as 1 em long. Some nodules 

entirely phosphatized; others are rimmed 

by phosphate. Siderite nodules rimmed 

with chlorite. One nodule has nucleus of 

fine-grained quartz and phosphatic sandstone which is rimmed by siltstone containing finely disseminated phosphate and 

quartz sand, which in turn is rimmed by 

very phosphatic siltstone. Some fragments 

of Lingula sp. 20.6 ft above base of unit 

are intermixed with subangular, subrounded, and well-rounded intraclasts of 

collophane (black) and collophane-rimmed 

siltstone and fine-grained sandstone. 

Clasts are as much as 2 em long and are 
34 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

Section 3-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Lizard Creek Member-Continued 

associated with subangular to subrounded 

quartz sand and pebbles (some pebbles 

are sandstone) as well as fragments of 

Lingula sp. Siderite occurs as nodules and 

in matrix. Some iron-mineral nodules 

have phosphate rim. Many phosphate 

nodules are penetrated by quartz sand 

and pebbles. Some phosphate nodules have 

soft-rock deformation features. Three 

higher nodule beds in unit consist of 

intermixed collophane nodules and quartz 

silt to pebbles. Some phosphate rims 

shale, siltstone, and sandstone intraclasts. 

Phosphate nodules subangular to well 

rounded and as much as 2 mm long. 

Quartz, siltstone, and sandstone occur as 

clay- to pebble-sized clasts and are angular to subrounded _____________________ 45.7 

71. Quartzite and shale. Very light gray (N8), 

greenish-gray (5GY 6/1) to medium-gray 

(N5), very fine to medium-grained (a 

few scattered coarse-grained beds), crossbedded (large-scale trough crossbedding) 

quartzite which contains rounded quartz 

pebbles as much as 14 in. long and scattered medium-dark-gray (N4) argillite 

intraclasts as much as 3 in. long; laminated and evenly to unevenly bedded; 

many beds lenticular and channeled; beds 

from near zero to as much as 8 ft thick; 

many beds contain thin irregular mediumgray (N5) shale intercalations. Mediumlight-gray (N6) to medium-dark-gray 

(N4) and dark-greenish-gray (5GY 4/1) 

laminated shale in beds less than 14 in. 

to as much as 2ft thick makes up 13 percent of unit. Shale interlaminated and 

finely interbedded with very fine grained 

quartzite locally. Olive shales become 

more abundant and sandstone less abunant toward top 20 ft of unit ___________ 145.0 

70. Quartzite, shale, and siltstone. Very light 

bluish white (5B 8/1) to medium-lightgray (N6) and light-olive-gray (5Y 6/1), 

very fine to fine-grained, evenly bedded 

and wavy bedded (rippled) partly crossbedded quartzite in beds less than 14 in. 

to as much as 1.5 ft thick makes up 55 

percent of unit. Medium-gray (N5) to 

light-olive-gray (5Y 6/1), laminated to 

mottled shale and siltstone in beds less 

than 14 in. to as much as 4 ft thick 

make up 45 percent of unit. Shale intraclasts as much as 1 in. long in many 

sandstones. Sandstones have laminations 

to low-angle cross laminations. A 2-in. collophane-siderite-chlorite bed lies 23 ft 4 in. 

below top of unit above a 1-ft-thick finegrained, medium-light-gray (N6), indistinctly horizontally laminated sandstone; 

Section 3-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Lizard Creek Member-Continued 

this bed is overlain by well-laminated 

medium-gray (N5) to greenish-gray 

(5GY 6/1), very fine grained sandstone 

and siltstone. Basal contact abrupt _____ 46.9 

69. Shale and quartzite. Light-olive-gray (5Y 

6/1) to greenish-gray (5GY 6/1) shale 

in beds less than 14 in. to as much as 

5 ft thick with thin lenses and discontinuous laminae of siltstone interbedded, 

unevenly interlaminated, and mottled with 

light-gray (N7) and medium-greenishgray (5G 5/1) very fine grained quartzite 

in beds less than 14 in. to as much as 10 

in. thick. An 8-in.-thick medium-lightgray (N6) fine-grained quartzite with 

abundant intraclasts as much as 2 in. 

long and coarse quartz grains lies 1.2 ft 

below top of unit. A nodule-intraclast bed 

also occurs 4 in. below top of unit. Its 

matrix is flaser-bedded shale, siltstone, 

and fine-grained sandstone. Nodules are 

siltstone to fine-grained sandstone which 

are phosphatic throughout or rimmed 

with phosphate. Nodules are as much as 

2.5 em long and are well rounded to subangular. Some iron-rich (siderite) nodules 

are also rimmed by chlorite. Many fragments of Lingula sp. Some well-rounded 

phosphate nodules penetrate phosphaterimmed siltstone intraclasts. Basal contact abrupt -------------------------- 12.0 

68. Quartzite, medium-gray (N5) to mediumdark-gray (N4), very fine to fine-grained, 

chloritic; some beds contain greenish-gray 

(5GY 6/1) shale intraclasts as much as 

% in. in diameter; beds are unevenly 

bedded, 1 in. to as much as 1 ft thick. 

Two 3-in.-thick beds at base of unit consist of very irregularly mottled to unevenly interbedded and lenticular shale 

and quartzite (flaser bedded). Some 

nodules of collophane and scattered fragments of Lingula sp. that weather dull 

white occur in subangular to subrounded fine- to medium-grained sandstone. Grains are predominantly quartz, 

but 5-10 percent are sand-sized phosphate. 

Basal contact abrupt __________________ 2.8 

67. Quartzite and shale. Dark-gray (N3) to 

medium-greenish-gray (5GY 5/1) and 

dusky-red-purple (5RP 3/2) to grayishred-purple (5RP 4/2), very fine to coarsegrained limonitic quartzite in uneven and 

lenticular beds, 1-11 in. thick, makes up 

50 percent of unit. These beds contain 

scattered subangular to subrounded quartz 

pebbles as much as % in. long; abundant 

intraclasts of phosphatic greenish-gray 

( 5G 6/1) shale to fine-grained sandstone 

as much as % in. long; numerous siderite­
MEASURED SECTIONS 35 

Section 3-Continued 

Shawangunk Formation-Continued Thickness

(ft) 

Lizard Creek Member-Continued 

chlorite nodules, 1-4 mm long; and linguloid brachiopod fragments. Rest of unit 

is greenish-gray (5GY 6/1) shale in beds 

as much as 3 in. thick. Basal contact 

abrupt ------------------------------ 5.0 

66. Shale, siltstone, and sandstone. Partly burrow mottled greenish-gray (5GY 6/1) to 

grayish-yellow-green (5GY 7/2) shale 

and irregularly interlaminated and lenticular light-gray (N7) siltstone and very 

fine grained calcareous sandstone in beds 

1 in. to as much as 4 ft thick constitute 

about 88 percent of unit and are interbedded with light-gray (N7), dark-greenish-gray ( 5G 4/1), and dusky-red-purple 

(5RP 4/1) very fine to medium-grained 

limonitic, hematitic, and magnetitic 

quartzite in beds (generally less than 

2 in. thick) and lenses (less than 0.5 to 

as much as 2 in. long). A 2-in.-thick 

nodule bed occurs 10 in. above base of 

unit. Bed is lenticular, and the shale and 

siltstone matrix is flaser bedded. Bed 

contains linguloid brachiopod fragments; 

color-zoned fine-grained phosphatized siltstone clasts in a pyritic, irregular, coarse 

siltstone to very fine grained sandstone 

matrix; and zoned nodules of, from center outward, dark-yellowish-orange (lOYR 

6/6) to pale-yellowish-orange (10YR 8/6) 

siderite rimmed with dark-yellowish-green 

(lOGY 4/4) chlorite (chlorite rims are 

about 0.02 mm thick). Nodules are elliptical to very irregular in shape, 2-20 mm 

long, and 1-4 mm thick. Some are not 

zoned. Interspersed with the nodules are 

coarse to very coarse angular grains of 

sand -------------------------------­ 7.8 

65. Quartzite and silty shale. Dusky-red-purple 

(5RP 3/2) to brownish-gray (5YR 4/1), 

very fine grained quartzite in beds 2 in. 

to 1 ft thick with many greenish-gray 

(5GY 6/1), half-inch-thick shale intercalations and irregular lenses. Basal foot 

consists of light-gray (N7), mediumgrained quartzite unevenly interbedded 

with greenish-gray laminated (5GY 6/1) 

shale and siltstone. Basal contact concealed ------------------------------- 6.0 

64.Covered ------------------------------ 192.3 

63. Quartzite, very light gray (N8) to lightgray (N7), medium-greenish-gray (5GY 

5/1), and· light-olive-gray (5Y 6/1), very 

fine to medium-grained with a few coarsegrained beds. Beds 2 in. to as much as 

2 ft thick ; thinner beds are finer grained 

and more evenly bedded to laminated, 

with small-scale scour-and-fill; thicker 

beds are coarser grained and unevenly 

Section 3-Continued 

Thickne88 Shawangunk Formation-Continued (ft) 

Lizard Creek Member-Continued 

bedded and contain scattered fragments 

of medium-dark-gray (N4) shale as much 

as 2 in. long. Quartzite generally unevenly 

bedded. A light-olive-gray (5Y 6/1) silty 

shale bed, 7 in. thick, occurs near middle 

of unit, and a few shale beds less than 

!A, in. thick are scattered throughout unit. 

Basal contact abrupt ------------------ 20.0 

62. Quartzite and shale, unevenly bedded and 

lenticular. Light-gray (N7), mediumgrained, limonitic qu.artzite and mediumgreenish-gray (5GY 5/1), very fine 

grained quartzite interbedded with laminated light-olive-gray (5Y 6/1) to greenish-gray (5GY 6/1) shale and shaly siltstone that weather grayish orange (lOYR 

7/4) to moderate brown (5YR 4/4); 

beds 1-4 in. thick. Basal contact .abrupt __ 2.7 

61. Quartzite and shale. Light-gray (N7), fineto coarse-grained limonitic unevenly 

bedded to laminated and cross-laminated 

quartzite in beds 8 in. to as much as 

2.3 ft thick containing scattered thin 

intercalations and fragments (as much as 

0.75 in. long) of medium-dark-gray (N4) 

silty shale. Intercalations are very irregularly bedded and contain medium- to 

coarse-grained, possibly burrow-mottled 

sandstone. Basal contact abrupt ______ _ 3.1 

60. Quartzite and siltstone. Dusky-red-purple 

(5RP 3/2) and light-olive-gray (5Y 6/1), 

very fine grained, poorly bedded quartzite 

in beds 4-6 in. thick interbedded with 

mottled greenish-gray (5GY 6/1) and 

pale-red-purple (5RP 6/2) shaly siltstone 

in beds 1-3 in. thick that has interlaminated and irregular pockets of very 

fine grained sandstone ________________ 3.2 

59. Quartzite, light-gray (N7) to moderategreenish-gray (5GY 5/1), fine- to mediumgrained, irregularly laminated to thickbedded with large-scale crossbedding; 

some beds contain scattered medium-gray 

(N5) shale pebbles as much as 4 in. long; 

beds 3 in. to as much as 3.5 ft thick. 

Basal contact abrupt _________________ 10.1 

58. Shale, siltstone, and quartzite. Light-olivegray (5Y 6/1) silty shale in beds 1-8 in. 

thick interbedded with light-olive (5Y 

6/1) -to medium-olive-gray (5Y 5/1) laminated siltstone to very fine grained 

vaguely laminated sandstone in beds 1-2 

in. thick and scattered beds of greenishgray (5GY 6/1) fine-grained quartzite 

in beds about 1 in. thick. Unit evenly 

bedded. Basal contact abrupt __________ 3.0 

57. Quartzite, light-gray (N7), fine- to mediumgrained; weathers light brown (5YR 

6/1); massive; very low angle cross lam­
36 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

Section 3-Continued 

Shawangunk Formation-Continued 

Lizard Creek Member-Continued 

Thickness 

(ft) 

inations and parallel bedding; low to 

moderate angle large-scale trough crossbedding; scattered pebbles of mediumdark-gray (N4) argillite as much as 0.75 

in. long ------------------------------ 2.1 

56. Shale, medium-olive-gray (5Y 5/1), silty, 

evenly laminated; one light-blue-gray 

(5B 7/1) very fine grained quartzite bed 

1.5 in. thick; basal contact abrupt _____ 1.1 

55. Quartzite, light-gray (N7) and greenishgray (5GY 6/1) to moderate-greenishgray (5GY 5/1), very fine to fine-grained, 

hematitic, generally poorly bedded, with 

thin discontinuous silty and fine sandy 

shale laminae as much as 1 in. long. A 

few beds contain medium-dark-gray (N4) 

silty shale fragments as much as 0.5 in. 

long; beds 4 in. to as much as 1 ft thick 

with scattered thin beds of greenishgray silty shale making up about 4 percent of unit. Quartzite has small-scale 

crossbedding and parallel laminations. 

Basal contact gradational and based on 

color 	change _________________________ 6.3 

54. Quartzite and shale. Medium-brownish-gray 

(5YR 5/1) to grayish-red-purple (5RP 

4/2), with a few medium-greenish-gray 

(5GY 5/1) mottles, very fine to finegrained indistinctly bedded hematitic 

quartzite in beds 1 in. to as much as 5 ft 

thick makes up most of unit, and pale-red 

(lOR 6/2) to light-brownish-gray (5YR 

6/1) shale in beds 0.25-4 in. thick makes 

up about 9 percent of unit. Shale is finely 

laminated to irregularly and indistinctly 

laminated with irregular sandstone-filled 

burrows. Scattered crossbeds. Basal con­ tact abrupt __________________________ 22.2 

53. Shale and quartzite. Medium-olive-gray (5Y 

5/1) moderate-orange-pink (5YR 8/4)­

weathering shale with discontinuous silt 

laminae and lenses; a greenish-gray very 

fine grained quartzite, 4 in. thick, occurs 

8-12 in. below top of unit. Basal contact 

abrupt ________ _______________________ 2.5 

52. Quartzite, medium-light-gray (N6), irregularly finely bedded to irregularly laminated; fine grained at top of unit and 

mottled greenish gray (5GY 6/1) and 

light brownish gray (5YR 6/1); very fine 

grained at base of unit; beds 4-8 in. 

thick; upper half of unit crossbedded and 

ripple marked (ripples are current type 

and indicate that current flowed to southeast) ; crossbedding indicates northwest 

flow; basal contact abrupt _____________ 1.6 

51. Siltstone and silty shale, mottled lightbrownish-gray (5YR 6/1) to moderatered-purple (5RP 5/2); moderate-redSection 3-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Lizard Creek Member-Continued 

purple beds are minor and are irregularly laminated; beds 3-7 in. thick; minor 

magnetite; basal contact abrupt ------- 3.0 

50. Quartzite, siltstone, and silty shale. Light 

(N7)-to medium-gray (N5) and greenishgray (5GY 6/1) very fine to fine-grained 

unevenly bedded quartzite in beds 1 in. 

to as much as 3.2 ft thick, but averaging 

about 10 in. thick, makes up 75 percent 

of unit. Quartzite interbedded with 

medium-dark- (N4) to medium-light-gray 

(N6) shale and siltstone which weather 

light olive gray (5Y 6/1), greenish gray 

(5GY 6/1), and grayish orange (10YR 

7/4) to grayish orange pink (5YR 7/2) 

and are in beds lh in. to as much as 1.5 

ft thick. Siltstone irregularly interlaminated with fine-grained sandstone (flaser 

bedded) and contains some burrow mottling. Beds and laminae even to uneven 

and lenticular ________________________ 34.0 

49. Like 	 unit 50. Very fine to fine-grained 

quartzite and siltstone in beds 1 in. to as 

much as 3.7 ft thick. Quartzite more abundant in upper half of unit. Shale partly 

micaceous and silty, laminated in beds less 

than 0.5 in. to as much as 2 ft thick, and 

makes up 4.5 ft of upper half of unit and 

9.5 ft of lower half of unit. Several beds 

crossbedded. Thick-bedded quartzites have 

large-scale crossbedding and planar bedding. Quartzites have low-angle to highangle trough crossbedding and are evenly 

and unevenly bedded. Quartzite and siltstone generally well laminated and have 

small-scale scour-and-fill ______________ 62.0 

48. Quartzite, dusky-red-purple (5RP 3/2) to 

grayish-red-purple (5RP 4/2), very fine 

grained, silty; beds 1.2-1.9 ft thick. Palered (5R 6/2) laminated silty shale bed, 

2 in. thick, occurs in middle of unit. Unit 

burrow mottled; contains small shale pebbles· sericitic small well-sorted lenses of 

ver; fine grained sand are reworked and 

made poorly sorted because of bioturbation --------------------------------- 6.2 

47. Shale, light-olive-gray (5Y 6/1); weathers 

moderate orange pink (5YR 8/4) to grayish orange (10YR 7/4); minor siltstone 

interlaminations and lenses (flaser bedding) ; indistinctly bedded; basal contact 

abrupt ------------------------------- 5.8 

46. Quartzite and siltstone, moderate-yellowishbrown (10YR 5/2) at base to moderategreenish-gray (5GY 5/1) above; laminated micaceous siltstone with minor 

burrowing at base to fine-grained quartzite above, limonitic and slightly pyritic; 

beds 3 in. to as much as 1.9 ft thick; 

color grades down into underlying unit__ 2.3 
MEASURED SECTIONS 37 

Section 3-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Lizard Creek Member-Continued 

45. Quartzite, well-sorted, and siltstone. Mottled 

and unevenly laminated grayish-redpurple (5RP 4/2) and dark-greenish-gray 

(5GY 4/1) very fine to fine-grained 

quartzite; beds 1-7 in. thick; fairly evenly 

bedded. A pale-red (5R 6/2) micaceous 

silty chloritic shale bed, 2 in. thick, occurs 

in middle of unit. Basal contact abrupt__ 2.3 

44. Quartzite and shale. Greenish-gray (5GY 

6/1) to moderate-greenish-gray (5GY 

5I 1) , very fine grained, evenly bedded and 

laminated (with minor cross laminations) 

quartzite in beds 2-6 in. thick interbedded with light-olive-gray (5Y 6/1) 

shale which weathers moderate orange 

pink (5YR 8/4) and moderate yellowish 

brown (lOYR 5/4) and is in beds 1-5 in. 

thick and makes up 33 percent of unit. 

Low-angle cross laminations. Basal contact abrupt -------------------------- 2.0 

43. Shale and quartzite. Greenish-gray (5GY 

6/1) to dark-greenish-gray (5GY 4/1), 

laminated to ripple laminated to unevenly laminated, partly burrow mottled, 

partly silty shale containing small-scale 

ripples; weathers pale yellowish orange 

(lOYR 8/6) and light brown (5YR 6/4); 

beds 2 in. to as much as 4.5 ft thick. 

Shale interbedded and interlaminated 

with very light gray (N8) to light-greenish-gray (5GY 8/1) limonitic quartzite 

in beds less than 0.5 in. to as much as 

6 in. thick; quartzite forms 10 percent of 

unit. Basal contact abrupt ____________ 11.2 

42. Quartzite, greenish-gray (5G 6/1), very 

fine grained; weathers into spheroidal 

blocks; massively bedded; minor pyrite. 

Basal contact abrupt _________________ 8.5 

41. Quartzite and shale. Medium-dark-gray 

(N4) and light-olive-gray (5Y 6/1), very 

fine to fine-grained quartzite in beds 

1 in. to as much as 1.5 ft thick interbedded with two 1-in.-thick grayishorange (lYR 8/4) irregularly laminated 

and burrow-mottled silty shale beds ____ 2.0 

40. Shale and quartzite. Mottled grayish-redpurple (5RP 4/2) and moderate-greenishgray (5GY 5/1) laminated and burrowmottled silty shale grading up into grayish-red-purple (5RP 4/2) silty shale, with 

a 10-in.-thick mottled grayish-red-purple 

(5RP 4/2) and moderate-greenish-gray 

(5GY 5/1) very fine grained limonitic 

quartzite abruptly overlying shale at top 

of unit. Basal contact abrupt __________ 4.0 

39. Sandstone, siltstone, and shale, interlaminated. Moderate-greenish-gray ( 5GY 

5/1), very fine grained sandstone grading up into siltstone which grades up into 

Section 3-Continued 

Shawangunk Formation-Continued Thickness

(ft) 

Lizard Creek Member-Continued 

light-olive (lOY 5/2) shale. Basal contact 

gradational -------------------------- 2.2 

38. Siltstone and sandstone. Mottled and colorlaminated grayish-red-purple (5RP 4/2) 

.and moderate-greenish-gray ( 5GY 5/1) 

laminated to cross-laminated (crossbed 

sets as much as half an inch thick) siltstone and very fine grained sandstone, 

4 in. thick, overlain by grayish-redpurple (5RP 5/2) massive burrow-mottled siltstone. Basal contact abrupt _____ 2.0 

37. Quartzite, siltstone, and silty shale. Lightgray (N7), dark-greenish-gray (5GY 

4/1), to greenish-gray (5GY 6/1), very 

fine to fine-grained, evenly bedded to laminated quartzite in beds 2 in. to as much 

as 1 ft thick with thin beds of greenishgray (5GY 6/1), grayish-yellow(5Y 8/4)­

to dark-yellowish-orange (lOYR 6/6)­

weathering, laminated, micaceous siltstone 

and silty shale in beds 0.5-1 in. thick. 

Siltstone and silty shale make up about 

3 percent of unit. Basal contact concealed ------------------------------- 6.7 

36. Covered ------------------------------- 20.0 

35. Shaly siltstone, silty shale, and quartzite. 

Yellowish-gray(5Y 811)-weathering to 

light-olive-gray (5Y 6/1)- and light-gray 

(N7) -weathering siltstone and shale unevenly laminated and in beds as much 

as 1 ft thick. Small-scale scour-and-fill 

structures and cross laminations. Beds 

contain scattered siltstone-filled burrows 

to very fine grained and fine-grained 

sandstone-filled burrows. Shaly siltstone 

and silty shale interbedded with lightgray (N7) very fine to fine-grained partly 

limonitic quartzite in beds 0.5-10 in. thick 

form 35 percent of unit; contains scattered flat argillite pebbles as much as 1.5 

in. long. One 1.5-inch-long siltstone pebble 

col1ected 3 ft above base of unit has concentric rims of siltstone and very thin 

rims of dark-gray (N3) phosphate. Basal 

contact abrupt _______________________ 10.0 

34. Quartzite, medium-light-gray (N6) to 

medium-gray (N5) very fine grained, 

well-sorted, unevenly bedded; beds 2-8 in. 

thick -------------------------------- 2.5 

33. Siltstone, shale, and quartzite. Mediumlight-gray (N6) to medium-dark-gray 

(N4) and light-olive-gray (5Y 6/1), unevenly to irregularly bedded and laminated, burrow-mottled silty mudstone and 

shaly siltstone which weather very pale 

orange (lOYR 8/2) to moderate yellowish 

orange (lOYR 7/6); unit contains abundant siltstone-filled to very fine grained 

sandstone-filled burrows. Burrows are par­
38 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

Section 3-Continued 

Thickness Shawangunk Formation-Continued (ft) 

Lizard Creek Member-Continued 

allel to bedding and are approximately 

0.25 in. in diameter. Shale interbedded and 

interlaminated with medium-light-gray 

(N6) and yellowish-gray (5Y 8/ 1) predominantly very fine grained, but in 

places medium-grained, quartzite which 

weathers very pale orange (lOYR 8/ 2) to 

moderate yellowish orange (10YR 7/ 6) 

and which occurs in beds of lenticular 

laminae (flaser bedded) as much as 1.8 

ft thick. Two quartzite beds, 1.8 and 0.85 

ft thick, lie 7.2 and 32 ft, respectively, 

above base of unit. Quartzite beds greater 

than 1 in. thick make up 17 percent of 

unit; sand-sized particles make up about 

40 percent of unit. Some quartzite beds 

contain pebbles of grayish-black (N2) 

shaly mudstone as much as 0.25 in. long. 

Some quartzite laminae have small-scale 

scour-and-fill structures. First appearance 

of laminated olive-green shale and interlaminated siltstone (with burrow mottles 

and flaser bedding). Basal contact con­ cealed ____ __ ______ _____________ ______ 50.5 

32. Covered ---------------- - -------------- 50.0 

31. Quartzite, greenish-gray (5GY 7/1), very 

fine grained; beds 3-11 in. thick; possibly a slump block; basal contact concealed ------------- - ----------------- 2.3 

30. Covered - - ------------ - ---------------- 23.2 

29. Quartzite, shaly siltstone, and silty shale. 

Light-olive-gray (5Y 6/ 1), light-bluishgray (5B 7/1), and light-gray (N7) very 

fine to fine-grained, partly limonitic 

quartzite in beds 2 in. to as much as 2.5 

ft thick. Many quartzite beds are ripple 

topped, some are finely bedded to laminated, and some are finely crossbedded. 

Quartzite interbedded and interlaminated 

with light-olive-gray (5Y 6/ 1) and mediumdark-gray (N4) to medium-light-gray (N6) 

evenly laminated to irregularly laminated 

shaly siltstone and silty shale in beds paper 

thin to as much as 0.5 ft thick. Some very 

fine lenticular interlaminations (less than 

1 mm thick) of shaly siltstone and quartzite have small-scale cross laminations. 

Basal contact concealed ____ _____ 29.5 

28. Quartzite and shaly siltstone. Light-olivegray (5Y 6/1) and medium-light-gray 

(N6) to very light gray (N8) limonitic 

partly crossbedded quartzite in beds 1 in. 

to as much as 8.5 ft thi ck. Many rippled 

surfaces (ripples with wavelengths of 

4 in. to 1 ft). Quartzite has large-scale 

crossbedding and planar bedding; contains thin smears of 2-in.-thick beds of 

light-olive-gray (5Y 6/ 1) shaly siltstone. 

Siltstone laminated to cross laminated, 

Section 3-Continued 

Thickn ess Shawangunk Formation-Continued (jt) 

Lizard Creek Member-Continued 

with sets as much as 0.5 in. thick; makes 

up about 2 percent of unit. Basal contact 

abrupt and undulatory with a relief of 

about 2 in. -------------------------- 32.8 

27. Quartzite and shaly siltstone. Light-gray 

(N7) and light-olive-gray (5Y 6/ 1), very 

fine to fine-grained quartzite and silty 

quartzite in uneven beds 1 in. to as much 

as 1.5 ft thick with light-olive-gray (5Y 

6/1) laminated and bioturbated shaly siltstone which makes up less than 2 percent 

of unit ------------------------- ------ 5.2 

26. Silty shale, shaly siltstone, and quartzite. 

Medium-light-gray (N6) to dark-gray 

(N3) and light-olive-gray (5Y 6/1) 

partly silty and indistinctly bedded to 

laminated silty shale and shaly siltstone. 

A few scattered lenses and beds of very 

fine to fine-grained quartzite make up 

about 0.5 ft of unit. Scatter d burrows 

parallel to bedding. Basal contact abrupt 

and uneven ______ _____ ___________ ___ _ 11.5 

25. Quartzite, siltstone, and shale. Light-gray 

(N7) to light-olive-gray (5Y 6/ 1) to 

greenish-gray (5GY 6/ 1), very fine to 

medium-grained, limonitic, moderatebrown (5YR 4/4)-weathering to darkyellowish-orange (lOYR 6/ 6)-weathering 

quartzite in beds and discontinuous lenses 

1 in. to as much as 1 ft thick, containing 

scattered specks of graphite and some 

coarse sand grains. These rocks are unevenly interbedded (flaser bedded) with 

medium-dark-gray (N4) to medium-gray 

(N5) and light-olive-gray (5Y 6/ 1) siltstone and lesser claystone which weather 

light gray (N7) and pale yellowish 

orange (lOYR 8/ 6) to dark yellowish 

orange (10YR 6/ 6). Well-laminated to 

irregularly laminated and burrow-mottled 

siltstone interlaminated with irregular 

lenses of fine- to medium-grained quartzite. Some siltstone is micaceous; some contains % -in.-diameter burrows that are 

filled with very fine to fine-grained sandstone. Burrows are parallel to bedding 

and anastomose. Some quartzite beds are 

crossbedded in sets about % in. thick. 

Basal contact concealed _____ _______ __ _ 28.0 

24. Covered ----- -------------------------- 30.0 

23. Quartzite, medium-dark-gray (N4) to 

medium-light-gray (N6), light-olive-gray 

(5Y 6/ 1), and light-brownish-gray (5YR 

6/ 1); medium- to coarse-grained (one 

3-in.-thick bed of very coarse grained 

quartzite with pebbles as much as 5 mm 

long) ; very unevenly bedded; beds 1 in. 

to as much as 1.3 ft thick; one 3-in.­
MEASURED SECTIONS 39 

Section 3-Continued 

Shawangunk Formation-Continued Thickness 

(ft) 

Lizard Creek Member-Continued 

thick bed of medium-gray (N5) shaly siltstone; basal contact concealed ___ ____ __ 10.0 

22. Covered. Float of quartzite and argillite; 

unit may be largely argillite. Very light 

gray (N8) to medium-gray (N5) very 

fine to medium-grained limonitic quartzite 

that has scattered pockets of coarser 

grain size that contain pebbles as much as 1

4 in. long. Medium-dark-gray (N4) and 

light-olive-gray (5Y 6/1) partly micaceous argillite (siltstone and minor shale). 

Thickness of unit is approximate _____ _ 110.0 

Total 	 thickness of Lizard Creek___ 

Member _______ __ _____ ___ ____ __ 1,224.4 

Minsi Member: 

21. Quartzite, very light gray (N8) to mediumlight-gray (N6) and greenish-gray (5GY 

6/ 1), medium-grained to very coarse 

grained, but predominantly mediumgrained; some beds contain white quartz 

pebbles as much as 1.0 in. long, but generally 0.5 in. long; greenish-gray (5GY 

6/1) argillite is widely scattered throughout unit as thin (less than 2 in. thick) 

beds and discontinuous flattened fragments as much as 3 in. long; quartzite 

beds 1 in. to 2.5 ft thick, averaging about 

0.5 ft thick, with conglomerate beds as 

much as 1 ft thick; quartzites have planar 

bedding and large-scale crossbedding; 

basal contact concealed -- - - --------- --- 52.5 

20. Covered --- - ---- ----- - --- - ------------- 42.4 

19. Quartzite, medium-light-gray (N6) to 

medium-dark-gray (N4) to greenish-gray 

(5GY 6/1), fine- to coarse-grained with 

subangular to rounded milky quartz pebbles as much as 0.5 in. long; beds 2 in. 

to 2 ft thick; planar bedding and largescale crossbedding; basal contact concealed - - - --- ------------- ------------ 12.3 

18. Covered __ _--- - - - --- - - --- - - - - - -------- - 29.7 

17. Quartzite and conglomeratic quartzite, 

medium-dark-gray (N 4) to greenish-gray 

(5GY 6/1); unevenly bedded; beds 1 in. 

to 2.3 ft thick with planar bedding and 

large-scale crossbedding; clasts chiefly 

milky quartz, but some are chert, as much 

as 0. 75 in. long; in a few thin beds (approx. 0.5 ft thick), clasts make up 5 percent of unit, but con stitute more than 50 

percent of total bed volume. A thin lightolive-gray (5Y 6/ 1) sandy siltstone occurs 

near top of unit. Basal contact con­ cealed ______ ____ ___ __ ____ __ __ ___ __ __ _ 20.8 

16. Covered - - ---- --- - ---- - - - --- ---- - --- --- 19.0 

15. Conglomeratic quartzite, quartzite, conglomerate, and argillite. Light-olive-gray 

Section 3-Continued 


Shawangunk Formation-Continued Thickneas 


(/t) 

Minsi Member-Continued 

(5Y 6/1) to greenish-gray (5GY 6/1) 

conglomeratic quartzite with a mediumgray (N5) to medium-dark-gray (N4) 

fine- to coarse-grained matrix; the 

rounded pebbles are chiefly quartz with 

some chert and are as much as 0.75 in. 

long and form about 10 percent of bed 

volume; beds 2 in. to 2.5 ft thick. Unit 

contains planar bedding and large-scale 

crossbedding. This lithology makes up 

about 70 percent of unit. Medium-gray 

(N5) to medium-dark-gray (N4) fine- to 

coarse-grained quartzite in beds 2 in. to 

2 ft thick with scattered subangular to 

rounded quartz pebbles as much as 0.5 in. 

long; quartzite constitutes about 15 percent of unit. Chiefly rounded chert- and 

quartz-pebble conglomerate with a medium-dark-gray (N4) quartzite matrix; 

a few argillite pebbles as much as 3 in. 

long; pebbles make up 25-50 percent of 

bed volume; beds 1 in. to 1 ft thick; 

conglomerate beds make up about 14 percent of unit. Medium-dark-gray (N4) 

to light-greenish-gray (5GY 8/1) argillite 

in beds 0.5-3 in. thick make up about 

1 percent of unit. Pebbles in unit become smaller upwards, averaging 1 in. 

in basal beds and about 0.5 in. in upper 

beds. Bedding uneven and lenticular, with 

many low-relief channels. Many surfaces 

are uneven and may be megarippled. 

A rth1·ophycus occurs 8 ft below top of 

unit. Unit partly covered above base; 

basal contact gradational ____ ________ __ 48.5 

Total thickness of Minsi Member ___ 225.2 

Weiders Member: 

14. Conglomerate; quartz and chert pebbles as 

much as 2 in. long in a greenish-gray 

(5GY 6/1) to dark-greenish-gray (5GY 

4/ 1) medium- to coarse-grained matrix; 

beds 1-2 ft thick; crossbeds subordinate to 

planar beds; a few greenish-gray (5GY 

6/ 1) argillite fragments (as much as 5 

in. long) and beds (as much as 1 in. 

thick) scattered throughout; a few thin 

(3-4 in. thick) greenish-gray (5GY 6/1) 

medium-grained to very coarse grained 

lenticular quartzite beds with quartz and 

chert pebbles; these conglomeratic quartzite beds are as much as 2 ft thick; pebble 

count of 100 pebbles, 0.75 in. long or 

greater, is as follows: vein quartz, 76; 

chert, 22; argillite, 2. Rock generally 

breaks through pebbles ________ ______ _ 12.2 

13. Quartzite, medium-dark-gray (N4), medium- to very coarse grained, slightly conglomeratic with chert .and vein quartz 
40 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

Section 3-Continued 

Shawangunk Formation-Continued Thickness (ft) 

Weiders Member-Continued 

pebbles as much as 0.75 in. long; a few 

thin (about 0.5 in. thick) greenish-gray 

(5GY 6/1) argillite beds ____ __ ______ 5.7 

12. Conglomerate and conglomeratic quartzite. 

Quartz-, chert-, and quartzite-pebble conglomerate; pebbles as much as 3 in. long 

in a moderate-greenish-gray (5GY 5/1) 

to medium-dark-gray (N4) mediumgrained to very coarse grained sandstone 

matrix; massive unevenly bedded (beds 

as much as 8 in. thick); makes up about 

50 percent of unit. Interbedded with conglomeratic medium- to coarse-grained 

partly crossbedded quartzite in uneven 

beds as much as 1 ft thick. Unit contains 

a few scattered black argillite pebbles _ 26.8 

11. Quartzite, conglomeratic quartzite, and conglomerate, medium-dark-gray (N4) to 

greenish-gray (5GY 6/1), mediumgrained to very coarse grained; pebbles 

as much as 2 in. long are mainly rounded 

milky quartz but include a few chert pebbles; argillite pebbles as much as 5 in. 

long; pebbles in a predominantly very 

coarse grained matrix; pebbles make up 

less than 50 percent of the volume of 

most beds ; beds 3 in. to 5.5 ft thick. Basal 

contact abrupt ____ _ _ _ 16.6 

10. Quartzite (generally clean quartzite with 

scattered specks of yellowish-gray-weathering (5 Y 811) shale and siltstone 

grains), yellowish-gray (5Y 8/1) to medium-dark-gray (N4) and yellowish-gray 

(5Y 8/ 1), fine- to medium-grained; with 

lesse r very coarse grained to conglomeratic quartzite beds that have quartz 

pebbles as much as 0.25 in. long and 

minor medium-dark-gray (N4) flat-pebble 

shal e clasts as much as 0.75 in. long. 

Beds 2 in. to 5 ft thick containing 

planar bedding and lesser crossbedding. 

A few surfaces are undulating, suggestive 

of mega ripples . Small-scale ripples with 

wavelengths of 1 in. occur in middle of 

unit. Basal contact gradational ·--·----- 58.0 

9. Conglomerate, containing subrounded to 

well-rounded quartz and chert pebbles as 

much as 3 in. long; flattened grayishblack (N2) shal e pebbles as much as 1 

in. long; medium-dark-gray (N4) very 

coarse to medium-grained sandy matrix; 

one single massive planar-bedded unit; 

pebble count of 100 pebbles greater than 

0.75 in. long is as follows: vein quartz, 

68; chert, 27; shale and siltstone, 3; 

quartzite, 2. Basal contact gradationaL _ 2.9 

8. Quartzite and conglomerate. Medium-gray 

(N5) to greenish-gray (5GY Gil) fineto coarse-grained, planar-bedded and 

Section 3-Continued 

Shawangunk Formation-Continued Thick-lrcu ( ft) 

Weiders Member-Continued 

crossbedded quartzite with scattered pebbles of chert and vein quartz as much as 

2.5 in. long and scattered gray argillite 

pebbles as much as 3 in. long in beds 2 

in. to 2 ft thick interbedded with chertpebble and vein quartz-pebble conglomerate (clasts similar to those in quartzite) in beds 2 in. to 2 ft thick. Lightolive-gray (5Y 611) lenticular shale in a 

2-in.-thick bed at base of unit and a halfinch bed 3.7 ft above base of unit; shale 

with two cleavages, the second cleavage 

in some cases localizEd near quartz pebblEs. Basal contact abrupt _______ ___ 26.6 

7. Conglomerate, containing subrounded to 

well-rounded chert and vein quartz pebbles as much as 2.5 in. long and flat pebbles of dark-gray (N3) to greenish-gray 

(5GY 6/ 1) argillite as much as 7 in. long 

in a greenish-gray (5GY 611) to medium-gray (N5) medium-grained to very 

coarse grained limonitic sandy matrix; 

pebbles make up about 50 percent of bed 

volume. Unit planar bedded. Basal contact abrupt _ _ _ __ ___ _ ___ _ _ ____ 6.7 

6. Quartzite, medium-gray (N5), medium- to 

coarse-grained; grains subangular to s ubrounded ; containing a few scattered chert 

pebbles as much as 0.5 in. long; massive; 

scattered masses of pyrite as much as 0.25 

in. long and specks of limonite pseudomorphic after pyrite; basal contact 

abrupt and irregular . _ _ ___ _ 4.5 

5. Conglomerate and quartzite. Well-rounded 

to subangular chert-pebble and veinquartz-pebble conglomerate in beds 2 in. 

to 1.2 ft thick with pebbles as much as 3 

in. long (a few scattered quartzite pebbles a s well as medium-gray (N5) to 

greenish-gray (5GY 6/ 1) flat argillite 

pebbles as much as 7.5 in. long with fissility parallel to bedding) in a greenishgray (5GY 6/1) to medium-gray (N5) 

medium-grained to very coarse grained 

sand matrix. Above rock type interbedded with greenish-gray (5GY 6/1) to 

medium-gray (N5) medium- to coarsegrained quartzite in beds ,2 in. to 1.3 ft 

thick; quartzite contains scattered pebbles 

as much as 1.5 in. long. Rock breaks 

across all pebbles. Count of 100 J?ebbles, 

all 0. 75 in. long or more, is as follows: 

chert, 56; vein quartz, 26; quartzite, 9; 

and shale and siltstone, 9 -----------·--- 4.9 

4. Quartzite, siltstone, and conglomerate. 

Medium-light-gray (N6) to greenishgray (5GY 611) medium- to coarsegrained slightly limonitic massive crossbedded quartzite with scattered chert and 
MEASURED 41 

Section 3-Continued 


Shawangunk Formation-Continued Thickness 


(ft) 

Weiders Member-Continued 

milky quartz pebbles as much as 1.5 in. 

long in beds 4 in. to 2.8 ft thick interbedded with thin lenses of greenish-gray 

(5GY 611) shale and three lenticular 

beds, 2, 5, and 7 in. thick, of planarbedded rounded to subrounded predominantly chert-pebble conglomerate (pebbles 

as much as 3 in. long). Basal contact 

abrupt and irregular _______________ _ 16.4 

3. Conglomerate and quartzite. Subrounded to 

rounded pebbles as much as 2.5 in. long 

of grayish-yellow-green ( 5G Y 712) to 

medium-dark-gray (N4) chert, white 

(N9) to very light gray (N8) vein quartz, 

quartzite, and lesser dark-gray (N3) 

argillite in a medium-gray (N5), medium- to coarse-grained, angular to subrounded quartz and chert sand matrix. 

Beds uneven, massive, spheroidally weathered, and 2 in. to 1 ft thick. Some 

quartzite pebbles have a partial moderatebrown(5YR 414)-weathering rind as 

much as 0.25 in. thick indicating predepositional weathering. A few thin beds 

of greenish-gray (5GY 611) to mediumgray (N6) medium- to coarse-grained 

limonitic quartzite in beds less than 0.5 ft 

thick. Rock breaks through pebbles. Basal 

contact abrupt and irregular _ _ ________ 5.3 

2. Conglomerate and sandstone. Leached; 

weathered moderate brown (5YR 414) to 

dark yellowish orange (lOYR 616). Rock 

is friable. Generally massively bedded 

with a few sandstone lenses. Conglomerate contains pebbles of sandstone, quartzite, conglomerate, chert, quartz, and argillite as much as 3 in. long. Sandstone 

pebbles are rounded to subrounded and 

generally very light gray (N8) to dark 

gray and weather pale olive (lOY 612) to 

light olive (lOY 512), dark yellowish 

orange (lOYR 616) to pale grayish 

orange (lOYR 814), and grayish orange 

(lOYR 714) to light brown (5YR 516). 

Sandstone is very fine to very coarse 

grained, some is conglomeratic with 

pebbles as much as 0.5 in. long, and 

some laminated. Many of the sandstones 

are pyritic, limonitic, or hematitic, and 

many are quartzites (have interlocking 

grain boundaries and are cemented with 

silica). Chert pebbles are medium dark 

gray (N 4) to grayish black (N2), and 

many are weathered pale yellowish 

orange (lOYR 816) to dark yellowish orange (lOYR 616) and white (N9). 

Argillite pebbles are common in basal 0.5 

ft and are as much as 2 in. long. These 

pebbles are shale and silty shale, are 

SECTIONS 

Section 3-Contiflued 

Thickneu Shawangunk Formation-Continued (ft) 

Weiders Member-Continued 

rounded to tabular, and are generally fissile parallel to bedding. Count of 100 pebbles greater than 0.75 in. long is as follows: sandstone and quartzite, 72; chert, 

21; vein quartz, 4; argillite, 3. Argillite 

pebbles are more abundant among the 

smaller sized pebbles . Sandstone in lentils 

as much as 4 in. thick, grayish orange 

(lOYR 714) weathering, poorly sorted, 

conglomeratic, fine to coarse grained. 

Basal contact abrupt and irregular _ _ _ 2.3 

Total thickness of Weiders Member 188.9 

Total thickness of Shawangunk 

Formation ___ ______ ____ ____ 1,638.5 

Martinsburg Formation (part): 

Pen Argyl Member (part): 

1. Claystone slate, medium-gray to dark-gray; 

weathers shades of orange, brown, and 

gray (light-olive-gray, 5Y 611; grayishorange, lOYR 7I 4; pale-yellowish-orange, 

lOYR 716; moderate-yellowish-brown, 

lOYR 514; grayish-red, 5R 412); bed 

thickness ranges from laminae to as much 

as 1 ft; interbedded with laminae and 

beds of grayish-orange ( 10 Y R 7I 4) -and 

moderate-brown-weathering graywacke 

sandstone and siltstone as much as 3 ft 

thick, containing flattened shale fragments as much as 2 in. long; some graywackes form base of fining-upward 

cycles; many are graded and have sharp 

erosional bases on pelite below. Graywacke makes up about 50 percent of unit 

and is most abundant in middle and at 

base. Slaty cleavage is well developed at 

base of unit and becomes very faint to 

absent within 175 ft of the contact with 

the overlying Shawangunk. Where cleavage is megascopically absent, the rock is 

predominantly a fissile shale; even here 

poorly developed cleavage folia can be 

seen microscopically. Bedding parting as 

well as bedding-plane slickensides become 

more apparent in the rock where cleavage 

is poorly developed. At the contact with 

the Shawangunk Formation is a 10-in.­

thick zone containing partly deformed 

Martinsburg, a quartz-filled slickenside 

zone, and a clay gouge and fault breccia 

with Martinsburg fragments. Base of unit 

concealed by talus ________ _____ ___ _ 293.0 

Incomplete thickness of Pen Argyl 

Member 293.0 

Incomplete thickness of Martinsburg 

Formation __ ___ __·_____ __ _______ 293.0 
42 SHAWANGUNK FORMATION, EASTERN PENNSYLVANIA 

Section 4 

[Weiders Member and part of the Minsi Me mber of the Shawangunk 

Formation along di1·t road on south side of Blue Mountain. 2,500 ft 

southwcRt of Bake Oven Knob, Slatedale <1uadrangle, Lehigh County, Pa. Beds dip 60- 70° NW.] 

Thicl.-u css (ft) 

Shawangunk Formation (part): 

Minsi Member (part): 

4. Quartzite, medium-grained to very coarse 

grained, conglomeratic, containing pebbles as much as 1 in. long. Top covered 140 

Incomplete thickness of Minsi Member 140 

Weiders Member: 

3. Conglomerate and quartzite. Beds 3 in. to 

1.5 ft thick. Pebbles generally not more 

than 1.5 in. long. Some pebbles about 

2 in. long, especially in upper 6 in. of 

unit. Quartzite is medium to very coarse 

grained 39 

2. Conglomerate, massive, pebbles as much as 

2.5 in. long 5 

1. Quartzite, coarse-grained to very coarse 

grained, conglomeratic; quartz pebbles as 

much as 2 in. long; probably at base of 

Shawangunk Formation; fragments of 

Martinsburg Formation in float about 5 

ft below stratigraphically 6 

Thickness of Weiders Member 50 

Incomplete thickness of Shawangunk 

Formation __ _ 190 

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