MISSISSIPPI AN SERIES. 25 
corresponds with the Kittanning bed of the surface, but sometimes with 
the Clarion or even with the Freeport sandstone. 
POTTSVILLE SANDSTONE, OR SALT SAND (POTTSVILLE FORMATION). 
Definition. — The Pottsville formation, frequently known as " the 
conglomerate/' is the lowest in the Pennsylvanian series. It occurs 
directly beneath the Allegheny formation, and usually lies uncon- 
formabiy on the Mauch Chunk. In some regions, however, it rests 
directly on the Burgoon or Big Injun sandstone. The Pottsville for- 
mation is the Salt sand of well drillers. 
Character and thickness.— hi portions of Pennsylvania where it is 
exposed the Pottsville consists of two or more very massive and fre- 
quently conglomeratic sandstones, in some places separated by thin 
shales, carrying fire clay and coal beds. As recorded in wells in the 
Amity quadrangle, the formation is a sandstone varying from 60 to 170 
feet in thickness and is frequently composed of two members, which 
probably correspond with the Homewood and Connoquenessing sand- 
stones of the Beaver Valley. Between them a bed of shale 10 to 30 
feet thick is sometimes reported and is probably equivalent to the 
Mercer member of other parts of Pennsylvania. Occasionally a 
record reports limestone in the Pottsville. The formation is a great 
source of salt water, which is encountered in drilling. 
MISSISSIPPIAN SERIES. 
ROCKS BETWEEN THE POTTSVILLE ("SALT SAND") AND BURGOON ("BIG INJUN ") SAND- 
STONES (MAUCH CHUNK formation). 
Definition. — The Mauch Chunk formation may be defined as the 
rocks included between the Pottsville formation above and the Bur- 
goon (Big Injun) sandstone below. The lower portion of the forma- 
tion consists of a thick limestone, known to drillers as the Big lime. 
This is identical with the Greenbrier limestone, which outcrops on 
Chestnut Ridge and Laurel Hill to the east and which was called by 
the Second Geological Survey the Mountain limestone. The Mauch 
Chunk is frequently spoken of as the Mauch Chunk red shale, but 
this designation is hardly appropriate, because in addition to the 
limestone it also contains shale of other colors and, locally, sandstone. 
Character and thickness. — The Mauch Chunk formation is variable 
in this part of Pennsylvania, as may be seen from the accompanying 
sample sections. In many records uncertainty exists regarding the 
upper limit of the formation, but in the absence of definite informa- 
tion the top is generally considered as coincident with the bottom of 
the thick sandstone overlying the red shale. The following records 
are typical of those in the Zollarsville field and vicinity. The great- 
est thickness recorded is about 200 feet, in the J. L. Thompson and 
other wells. From 50 to 90 feet of this is red shale, 50 to 100 feet at 
the bottom is limestone, and the rest is shale. 
