GENERAL GEOLOGY OF CLAYSYILLE QUADRANGLE. 
57 
drawn to wells in the Burgettstown and Steubenville quadrangles, 
which go down to the Hundred-foot sand, the distance from this sand 
to the Gordon being estimated. Along these lines and in several 
other places throughout the quadrangle the isochor lines have not 
been drawn proportionally between wells, for the reasons given above. 
DISCUSSION OF CONDITIONS AS SHOWN BY MAP OF GORDON 
SAND. 
DESCRIPTION OF MAP. 
Within this quadrangle every principal sandstone bed from the 
Gas sand to the Fifth has produced more or less oil or gas. Nearly 
all of this yield comes, however, from the Gantz, Gordon Stray, Gor- 
don, Fourth, and Fifth, the Gordon easilv leading: both in area of 
producing sand and in amount of oil and gas furnished. On PI. 
XIII wells getting their oil or gas from the shallow and upper sands, 
down to and including the Gantz, are represented in orange, those 
from this horizon through the Gordon in red, and those from the 
Fourth and Fifth in blue. In areas where each well produces from 
two or more of these groups alternate wells have been given the colors 
of the groups represented. Many records do not show from what 
group the oil comes; these and all dry holes, together with the struc¬ 
tural contours on the Gordon sand, are also in red. The above out¬ 
lined division is only a general one. A large number of wells in this 
territory have been exhausted and abandoned. Many of these old 
wells were not located in the course of the field work, and no informa¬ 
tion could be had in regard to some of those that were located. The 
incompleteness of the records also makes a correct grouping of all 
the wells impossible. 
The Gordon sand lies between 1,000 and 2,000 feet below sea level. 
In order to avoid the confusion likely to arise from the use of minus 
elevations a datum plane 2,000 feet below sea level was selected from 
which to draw the structural contours on this sand. The contours 
are numbered in feet above this datum plane, and to ascertain the 
depth below sea level of the sand at any point it is necessary only to 
subtract the elevation of the contour at that point from 2,000 feet. 
STRUCTURE OF GORDON SAND. 
The structure of the Gordon sand as shown by these contours con¬ 
forms in a general way to that already given for the surface rocks, 
though in detail it is at many points quite different. The more 
important of these variations are referred to on page 55. This 
structure throughout the productive area is shown in greater detail 
than that of the surface rocks. Level lines were run to hundreds of 
wells in which the distance to the sand was given by the record, 
