THE TEXAS FIELDS 70'7 



not decline rapidly, and the grade of oil is well up toward the best of the 

 entire province. 



The nature of the rock folding in Texas was different from that of the 

 oil regions of Oklahoma and Kansas, in that the total stratigraphic sec- 

 tion of the rocks in Texas was .sufficiently competent to withstand in a 

 large degree the forces that reacted on them. The local structures lie in 

 widely separated localities rather than being bunched together irregu- 

 larly, such as is characteristic of the main fields of eastern Oklahoma and 

 Kansas to the north. Either the sedimentary beds in Oklalioma and 

 Kansas were less able to resist the tectonic forces acting against them or 

 else the disturbances in the Arbuckle and Ozark regions were more far 

 reaching in their effects than those of the Llano-Burnet uplift. 



In the Pennsylvanian area of Texas the rocks dip westward at an 

 average rate of about 20 feet per mile. It is rather unusual to find a 

 local area where there has been sufficient vertical movement to reverse 

 this dip. The oil-bearing structures at Moran, Strawn, and Corsicana 

 are essentially terraces, -although they contain a few closing contours of 

 ten feet interval. This condition is typical of a large portion of Electra 

 and Burkburnett districts, but the Petrolia field and that of Mexia, for 

 example, show^ anticlinal conditions which are more pronounced, as illus- 

 trated by the accompanying contour sketch of the Petrolia field (see 

 figure 7). 



As described by Shaw, the central portion of north Texas shows a broad 

 "upwarp" or low geanticline, with its axis lying in a north-south direc- 

 tion, from which the Pennsylvanian strata dip westward, while on the 

 east flank the unconformable sediments of the Cretaceous dip eastward. 

 Whether or not beds below the Cretaceous dip eastward to conform with 

 the younger formations is not known, nor has the actual presence of the 

 Pennsylvanian strata on the east side been determined. The fact is dem- 

 onstrated, however, that the Cretaceous strata follow the general structure 

 of the older formations on the west flank. While these younger beds on 

 the east flank outcrop west of Fort Worth and the projection of their 

 horizon westward carries above the surface over the area of the Pennsyl- 

 vanian and Permian, they appear again and lie at a low surface level in 

 the Panhandle region ; so it appears probable that a post-Cretaceous move- 

 ment acted along the axis of an older structure, thus producing a broad 

 geanticline over a broad area lying between the Arbuckle-A¥ichita region 

 of Oklahoma and that of the Llano-Burnet region of Texas. The latter 

 has been described by Sidney Paige in Folio Number 183 of the United 

 States Geological Survey. This condition would possibly explain the fact 

 that such a broad area of the outcropping strata is not folded into subordi- 



