124 ECONOMIC GEOLOGY OF AMITY QUADRANGLE, PA. 
limestone. Where exposed it is a hard, compact light-grayish or 
flesh-colored rock, usually coarsely brecciated and containing numer- 
ous spots of crystalline calcite, many of them replacing fossil shells. 
The limestone can generally be recognized by the great quantity of 
iron it contains, giving it a weathered surface of bright yellow, which 
in many exposures extends to a depth of several inches and finally 
exfoliates and crumbles off. Some of the basal layers are more earthy 
and slaty and do not have this characteristic. The bed is locally 10 to 
20 feet thick, but usually much thinner. 
The Middle Washington limestone has a wide distribution in the 
quadrangle, but its typical occurrence is near Washington. In a cut 
of the Baltimore and Ohio Railroad in the eastern part of the town the 
large yellow bowlders from the bed are finely exposed. This lime- 
stone has never been used and does not appear to be of value. 
JOLLYTOWN LIMESTONE. 
In accordance with the usage of Stevenson (1876), this term is 
applied to the limestone occurring above the Jollytown coal and 30 to 
K) feet below the Upper Washington. It is a hard, grayish, locally 
brecciated limestone, weathering light gray to dirty yellow. Owing 
to its peculiar character it is a good key rock. It is in places several 
feet thick, and appears below the Upper Washington limestone on most 
of the roads in the southwestern part of the quadrangle and in a few 
places elsewhere. 
UPPER WASHINGTON LIMESTONE. 
The Upper Washington limestone is the topmost bed of the Wash- 
ington formation and, with the exception of the Waynesburg sand- 
stone, is the most conspicuous and persistent member of the Dunkard 
group. For this reason it was chosen as the best horizon at which 
to subdivide the group into formations. It occurs 630 to 710 feet; 
above the Pittsburg coal and 280 to 400 feet above the Waynesburg 
coal. The outcrop of this limestone throughout the quadrangle is 
represented on the geologic map (PL I, pocket) by the heavy green 
line separating the Washington and Greene formations. 
The characteristics of the Upper Washington limestone are rather 
distinctive. It is hard, compact, and brittle, and is generally made 
up of a number of layers separated by thin beds of shale. Through- 
out the greater part of Washington County its upper part on fresh 
fracture has a dark blue-gray, bluish black, or even nearly black 
color. Generally it contains drab and mottled layers. The rock as 
a rule is very pure. In some portions of the district it is easily recog- 
nized by its weathered surface, which is almost snowy- white, with a 
slight tinge of blue. It varies in thickness from 4 to 30 feet. 
The best exposures of this limestone arc to be seen in the vicinity 
