708 J. H. GARDNER THE MID-CONTINENT OIL FIELDS 



nate structiu'es ; probably the stresses from the two regions of maximum 

 movement were to a notable extent relieved by the general rise of the 

 intervening strata. This broad, low arch in central Texas is perhaps 

 related in origin, as it is in size and form, to the Sabine uplift in north- 

 ern Louisiana, which lies directly to the east. There is a well defined, 

 broad structural basin between the two uplifts, in which lie the deposits 

 of the Cretaceous and Tertiary systems. The Caddo oil field is situated 

 on the north side of the Sabine structure. 



FiGDEE 7. — Structure Contour Map of Petrolia Oil and Gas Field, Texas 

 From BuUetin 623, United States Geologcial Survey 



The oil in the Toyah field, in the extreme western portion of Texas, 

 is found in the Delaware Mountain limestone member of the Permian, 

 which series is covered by the Washita group of the Comanche series. 

 C. A. Fisher has stated that the oil occurs on a monocline dipping 5 to 7 

 degrees eastward ; hence it seems probable that this region lies beyond the 

 effects of the earth movements above mentioned and is related to com- 

 pressive stresses that were initiated farther to the west, and have shown a 

 tendency to adjust themselves by an eastward tlirust along the west flank 



