ILLUSTRATIONS. 
v Page. 
Plate I. Diagrammatic section of sands in central Appalachian oil region_ 10 
II. Map showing distribution of gas and oil fields in western Pennsyl¬ 
vania and adjacent regions. 20 
III. Map of Steubenville quadrangle, showing key horizon (base of Pitts¬ 
burg coal) and location of bench marks. Pocket. 
IV. Subsurface stratigraphy of Steubenville quadrangle, showing conver¬ 
gence of Berea sand with respect to Ames limestone. 30 
V.' Convergence sheet of Steubenville quadrangle. Pocket. 
VI. Map of Steubenville quadrangle, showing contours on top of Berea 
oil sand, oil wells, and gas wells. Pocket. 
VII. Map of Burgettstown quadrangle, showing key horizon (base of Pitts¬ 
burg coal) and location of bench marks. Pocket. 
VIII. Convergence sheet of Burgettstown quadrangle. Pocket. 
IX. Map of Burgettstown quadrangle, showing contours on top of Hun¬ 
dred-foot sand, oil wells, and gas wells. Pocket. 
X.' Map of Claysville quadrangle, showing structure of surface rocks by 
contours on top of U-pper Washington limestone. Pocket. 
XI. Sections of deep wells in Claysville quadrangle. 52 
XII. Convergence sheet of Claysville quadrangle. Pocket. 
XIII. Map of Claysville quadrangle, showing contours on top of Gordon 
sand, oil wells, and gas wells. Pocket. 
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