52 
OIL AND GAS; OHIO, WEST VIRGINIA, PENNSYLVANIA. 
CONTOUR MAP OF UPPER WASHINGTON LIMESTONE. 
To reduce the elevations taken on other horizons than the Upper 
Washington limestone to the equivalent elevation of that stratum, 
the mean intervals mentioned above for each marking stratum have 
been used with few exceptions. Over a considerable portion of the 
northeast corner of the quadrangle, where the horizons of the Upper 
Washington limestone and the Washington coal are above the highest 
hills, and the Waynesburg coal is too thin to be easily recognized, 
the surface structure has been mapped from the Pittsburg coal as a 
secondare kev horizon. To the elevations of this coal, as given in 
numerous oil wells and bv the map of the Arden mine, was added an 
interval of 575 feet to determine the position of the key rock. This 
amount is the mean of all measurements obtained from wells along 
the east line of outcrop of the Washington coal and Upper Washing¬ 
ton limestone. The map of the surface structure in the northeast 
corner of the quadrangle, as made from these elevations, may be in 
error in certain places in amount equal to the difference between this 
mean interval and the true one between the Pittsburg coal and Upper 
Washington limestone at those places. 
With these elevations established on the Upper Washington lime¬ 
stone over the whole quadrangle, a map of the surface structure, as 
shown by the key rock, was easily made by drawing contour lines 
(level lines) connecting points of equal elevation. On PI. X con¬ 
tour lines showing the structural position of the surface rocks are 
printed in green on the topographic base map. These lines have a 
contour interval of 10 feet and are numbered with reference to their 
distance in feet above sea level. 
By a study of these contours it will be seen that the Upper Wash¬ 
ington limestone, together with the other surface rocks of the Clays- 
ville quadrangle (which were first laid down under water in fairly 
horizontal layers), in being raised to its present position has been 
subjected to more or less wrinkling. This folding or wrinkling 
results in structural features of two general types—(«) the “ highs,” 
or irregularly ridge-like anticlines, the tops of some of which cul¬ 
minate in small domes, and (b) low troughs or synclines, the bottoms 
of which here and there form shallow basins. 
WASHINGTON ANTICLINE. 
The most prominent anticline crossing the Claysville quadrangle 
enters it from the east a short distance from Arden station on the 
Pennsylvania Railroad, 3 miles north of Washington. The crest of 
this ridge, which is called the Washington anticline, pitches very 
steeply toward West Washington, reaching the bottom of a * low 
saddle between two domes about 1 mile to the southwest of this town, 
