ECONOMIC GEOLOGY OF THE AMITY QUADRANGLE, 
EASTERN WASHINGTON COUNTY, PA. 
By Frederick G. Clapp. 
INTRODUCTION. 
The Amity quadrangle lies in the southwest corner of Pennsyl- 
vania, and includes a portion of eastern Washington County and two 
small areas in northern Greene County. It extends from latitude 
40° to 40° 15' and from longitude 30° to 80° 15', and comprises an 
area of 228.4 square miles. It is bounded by the following quad- 
rangles: On the north by Carnegie, on the east by Brownsville, on the 
south by Waynesburg, and on the west by Claysville. The largest 
town is Washington, which had in 1900 a population of 14,117. 
The principal lines of transportation in the region are the Pitts- 
burg, Cincinnati, Chicago and St. Louis division of the Pennsyl- 
vania lines and the Pittsburg and Wheeling branch of the Baltimore 
and Ohio Railroad, both of which pass through Washington. The 
Waynesburg and Washington Railroad, a part of the Pennsylvania 
system, is a narrow-gage line running south from Washington to 
Waynesburg, in Greene County. Along South Branch of Pigeon 
Creek a branch of the Pennsylvania Railroad has been built as far 
as the mines at Three and Four. 
The main economic interest in this area lies in the facts that it has 
been the seat of extensive oil and gas development, and that it is 
almost entirely underlain by at least one valuable seam of bituminous 
coal. By reference to fig. 4 (p. 89) it will be seen that the quad- 
rangle is located near the center of the north end of the Pittsburg 
coal field. 
The field work on which this report is based was done by the writer 
and Frank W. De Wolf in July and August, 1904. 
COMMERCIAL GEOGRAPHY. 
The surface relief of a region is always important in connection 
with the development of its mineral resources, and in the Amity 
quadrangle, especially, it is necessary to know something of the 
topography in order to plan for future economic operations. The 
amount of relief or difference in altitude between the highest hilltops 
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