ABSTRACTS OF PAPERS 71 



Due to faulting, reliable stratigraphic sections have heretofore been diflBcult 

 to obtain, but microscopic studies of well samples and studies of the large 

 group of well logs yield much new information on the thickness of the several 

 formations, the a real extent of the Woodbine sand, the development of Taylor 

 chalk beds, and more precise location of contacts of Nacatoch, Midway, and 

 Wilcox. 



Pointing out. first, the larger structural relationships, we describe the Mexia 

 Fault Zone, 5 miles wide and 150 miles long, lying 20 to 30 miles east of 

 and parallel to the Balcones Fault Zone, These zones prove similar in char- 

 acter, with three or more normal, parallel faults, arranged en echelon with 

 "similar groups of faults lengthwise of the zone, accompanied by folding, always 

 faulted. Cross-faulting is absent. Both zones follow rigid rock outcrops off- 

 setting shale formations on their west. The Mexia zone effects a partial cut- 

 ting off of ground waters and appearance of connate waters in connection with 

 oil east of its easternmost faults, resulting in development of four oil pools. 



A stratigraphic table, together with cross and longitudinal sections, delineate 

 stratigraphic variations ; a sketch map shows relationship of major structural 

 features, and a detailed contour map of a segment of the fault zone shows its 

 local character. 



Part II. Origin of Structure, by Heath M. Robinsox 



An analysis of the stresses producing faults as applicable to the structure 

 under consideration is first discussed ; next, the character of the stresses pro- 

 ducing faults within described area is treated, showing that dominant stresses 

 are vertical. The zone of offset faults suggests a general weak zone. We then 

 discuss relationship between primary and secondary structural features in the 

 tilting of the Gulf Coast area toward the sea. pointing out the genetic rela- 

 tionship between them. The competency of Upper, Lower, and Pre-Cretaceous 

 beds to transmit stresses is discussed. The general conclusion is reached that 

 movement along deep-lying faults operating on underlying competent beds 

 would produce structural features on the surface beds similar to those found 

 within described area. 



Read in full from manuscript. 



Brief remarks were made by Dr. Sidney Powers and others. 



THE LAXCE PROBLEM 

 BY FREEMAN WARD ^ 



{Ahstract) 



Evidence from formations in South Dakota. Brief statement of facts on 

 which there is agi-eemeut : also of points mider controversy. Discussion of 

 contact of Fox Hills and Lance. Attempt to harmonize conflicting paleonto- 

 logic evidence. Break between Mesozoic and Cenozoic placed at top of Fort 

 Union. 



Read bv title. 



^ Introduced by H. E. Gregory. 



