40 
OIL AND GAS; OHIO, WEST VIRGINIA, PENNSYLVANIA. 
remarkably constant, being the same for short distances as for long 
distances. Thus the variation of interval between the Pittsburg coal 
and the limestone closely underlying it is nearly 20 feet, and the 
range of intervals between the Pittsburg coal and the Bulger limestone 
and between the Pittsburg coal and the Waynesburg coal, distances 
of 165 and 270 feet, respectively, is about the same. With a range of 
results of 20 feet, the average is probably correct within 10 or 15 feet. 
The limit of error, therefore, in the map showing the structure of 
the Pittsburg coal should be within 10 or 15 feet at points where 
outcrops were located. Between such locations the difference of 
elevation is spaced in by the contour lines, the correctness of which 
depends on the number of located points. About 600 geologic loca¬ 
tions were made in the quadrangle, the positions of which are shown 
on the map (PI. VII). Three small areas are noticeably deficient in 
information. The apparent absence of the Ames limestone on Kings 
Creek and the uncertainty regarding the identity of the coal bed there 
exposed leave a number of square miles without reliable data. In a 
small area near and to the north of Bavington the Ames limestone is 
not exposed, and the hills are not high enough to catch the Pittsburg 
coal. This small area could be easily spanned by contours were it 
not for the fact that the coal on the west side of the creek is in a 
syncline and that to the east nearly on the crest of an anticline, there 
being a difference of 60 or 70 feet in the elevations. Owing to 
this absence of outcrops of marking strata the east side of the 
syncline is not well defined. In the main synclinal trough southeast 
of Cross Creek the located outcrops are good, but few in number. 
The map of this area could be improved by level work off the roads, 
but the present work did not seem to warrant this expense. With 
these exceptions the representation of the surface structure shown on 
PI. A II is believed to be fully up to the contour limit of accuracy. 
STRUCTURE. 
The geologic structure represented by the contour lines on PI. VII 
brings out prominently the results of the two systems of folds that 
are present in the Burgettstown quadrangle. These systems are at 
right angles to each other, with strikes a little east of north for the 
major system and north of west for the minor system. The com¬ 
pression in an east-west direction has formed anticlinal ridges and 
synclinal troughs, whereas the compression in a north-south direc¬ 
tion has formed hardly more than monoclines and terraces, with the 
strong dips of the monoclines to the south. The combination of 
these two systems has formed a number of domes, terraces, and 
basins. 
