144 
KIRTLEY F. MATHER AND MAURICE G. MEHL 
man interested in the oil and gas resources of the region repre- 
sented: (1) the location and extent of the areas beneath which 
oil and gas migrating up the dip of the reservoir rocks would 
be trapped; (2) the size of the area from which the mobile hydro- 
carbons might be expected to move toward this trap. The first 
of these is important in determining the location of drill holes; 
the second is an equally important factor in determining the 
volume of possible production from the favorable structure. 
To those uninitiated into the mysteries of contour lines — and 
many such must constantly be dealt with in the petroleum 
industry — neither of these facts is apparent from the ordinary 
structure contour map. If the structure of the region be at all 
complicated, even the connoisseur must spend much time in a 
careful analysis of the contour lines before he can visualize the 
structure in all its details and grasp adequately the information 
thereby set forth. It has been found helpful in the interpreta- 
tion of structure contours to draft an auxiliary map so planned 
as immediately to focus the attention upon these two facts 
undistracted by a maze of lines. 
To illustrate the method and the result, there is presented 
herewith a structure contour map (plate XIX) of the four town- 
ships in the southwestern corner of the Pawhuska Quadrangle, 
Osage County, Oklahoma. The contour lines, redrawn from the 
township plats prepared by Heald, Winchester, Bowen, Condit, 
Emery, Clark and Mather, ^ represent a region of complicated 
structure comprising 31 anticlines and domes of sufficient indi- 
viduality to be given distinctive names. Accompanying this 
contour map is an oversheet reproduced from a map prepared 
by N. L. Thomas, a member of our class in petroleum geology, 
delineating the area of each inverted basin and drainage tract. 
The space embraced within the lowest closed contour line on 
each anticlinal fold is diagonally ruled; the direction of migration 
of oil or gas in the reservoir rock is indicated by arrows; the feed- 
ing ground from which the hydrocarbons, accumulated on or 
1 Structure and oil and gas resources of the Osage Reservation, Oklahoma, 
Twps. 24 and 25 N., Rs. 8 and 9 E., U. S. Geol. Survey, Bull. 686, parts E, M and 
P, 1918-1919. 
