GRiswoLD] STRUCTURAL WORK IN EASTERN OHIO OIL FIELDS. 33V) 
METHOD OF CONSTRUCTING MAP OF THE OIL SAND. 
Each outcrop was carefully located upon a topographic map previ- 
ously made by the Geological Survey, and from the bench marks 
established by the Survey a spirit-level line was run to each outcrop, 
establishing its exact position above sea level. Then by adding to 
or subtracting from the elevation of the outcrop an amount equal to 
the vertical distance at that point between the bed leveled to and the 
Pittsburg coal the elevation of the Pittsburg coal at that point was 
determined. In this way the true altitude of the key horizon (in this 
case the Pittsburg coal) was established at five or six hundred places 
over the quadrangle. By connecting the points of equal elevation a 
contour map of the key horizon was constructed. The position of 
each oil well which had been drilled in the quadrangle was care 
fully located upon the topographic sheet. Spirit-level lines were run 
to the mouth of each well, establishing its elevation above sea. In 
most cases the steel-tape measurement of the distance from mouth of 
well to the Berea grit sand was obtained from those interested in the 
wells. By comparing the elevation of the mouth of the well to the 
contour map of the key horizon the distance from this horizon to the 
cap of the Berea grit sand was determined in different portions of the 
quadrangle. The distance was found to vary, increasing gradually 
toward the southeast. At the position of each test well the vertical 
distance between the Pittsburg coal and the Berea grit was marked 
upon the map. 
The positions of the different test wells were connected by straight 
lines, and these lines were divided so that each subdivision repre- 
sented the horizontal distance in which the vertical distance from the 
Pittsburg coal to the Berea grit decreased 5 feet. The points of equi- 
distance from coal to sand were then connected, and a drawing was 
constructed, called the " convergence sheet." This shows by a series 
of lines the points of equal distance between the Pittsburg coal and 
the Berea grit. The convergence sheet was then placed over the plat 
showing elevations of the key horizon, and it showed at once the 
amount that should be subtracted from the elevation of the Pittsburg 
coal to determine the elevation of the Berea sand at any point. The 
elevation of the Berea sand at every point where it was determined 
was then marked upon the map and the points of equal elevat ion 
were again connected, resulting in a contour map of the oil-bearing 
sand. 
STRUCTURE OF BEREA GRIT. 
The contour map of the Berea grit sand shows a system of parallel 
folds in a northeast-southwest direction, crossed at nearly right angles 
by a system of broader and less pronounced folds, which break up the 
major structures into a series of elongated domes and canoe-shaped 
basins very similar to those of western Pennsylvania, as delineated 
by Mr. M. R. Campbell. 
