STRATIGRAPHY. 11 
oil tanks, in which oil from the Washington and Greene county fields 
is stored. Pipe lines, however, follow both valleys and uplands. 
STRATIGRAPHY. 
GENERAL STATEMENT. 
With the exception of a few comparatively recent deposits in the 
valleys, the rocks exposed at the surface of the quadrangle are all of 
Carboniferous age. They belong chiefly to the Monongahela, Wash- 
ington, and Greene formations, but the Conemaugh reaches the surface 
in two small patches. The formations which do not outcrop, but 
which are penetrated by deep wells, include, from the top downward, 
the Conemaugh, Allegheny, Pottsville, Mauch Chunk, and Pocono 
formations of the Carboniferous system, and part of the Chemung for- 
mation of the Devonian system. Below the Chemung lie thousands 
of feet of buried strata which have never been reached by the drill in 
this territory. The general relations of the various beds are shown 
for the formations which outcrop in the columnar section (PL I, in 
pocket), and for those which do not outcrop in fig. 1 (p. 20). 
Although the general relations of the beds are fairly constant, there 
are considerable variations in details in different parts of the area. 
Sections a number of miles apart, and even those within a short dis- 
tance of each other, are likely to differ somewhat in the character and 
thickness of the various beds. This is especially true of the forma- 
tions which do not outcrop, as reported in well sections. Over widely 
extended regions, however, uniform conditions prevailed and sedi- 
mentation resulted in strata without much variation at the same hori- 
zon. Such horizons serve useful purposes in geologic correlation, and 
are frequently of economic importance. The Pittsburg coal, the 
Waynesburg sandstone, the Upper Washington limestone, the Salt 
sand and the Big lime are examples of strata that are persistent over 
wide areas. The geologic map of the Amity quadrangle is shown in 
PI. L, in pocket. 
SURFACE ROCKS. 
From the highest to the lowest exposed horizon in this quadrangle 
the vertical thickness of the strata is about 1,200 feet, the highest 
point stratigraphically being in the hills in Morris Township, Greene 
County. The rocks are chiefly sandstones, limestones, and shales, 
but in the Monongahela and Washington formations several valuable 
coal beds occur. 
CARBONIFEROUS SYSTEM. 
ROCKS ABOVE THE WAYNESBURG COAL (DUNKARD GROUP OR PERMIAN SERIES). 
THE GROUP AS A WHOLE. 
Definition. — The Dunkard group, knowm in a broader geologic sense 
as the Permian series, includes all rocks from the top of the Waynes- 
