Weno and Pawpaw Formations 41 



paw formations in North Texas. Turrilites brazoensis, also a fossil of very 

 limited vertical range, marks the top of the Georgetown limestone and 

 the base of the Del Rio clay in Central Texas from the Brazos southwards. 

 The basal Mainstreet then is represented by the uppermost Georgetown in 

 Central Texas, and the Pawpaw if present by strata lying high in the 

 Georgetown, while the bulk of the lower Del Rio (Exogyra arietina zone) 

 is Mainstreet and the upper Del Rio is Grayson. 



WEST TEXAS AND MEXICO 



West of the southern turning point of the Comanchean outcrops in Bexar 

 County, the Georgetown limestone and the Del Rio clay preserve their in- 

 dividuality into the Trans-Pecos region. At the type locality of the Del 

 Rio clay, it is typically developed as a laminated, greenish-blue clay with 

 thin instratified arenaceous clay seams, calcareous flags and shell breccia 

 (Exogyra arietina and Noslosaria texana) . In lithology this formation 

 "varies from a clay to an arenaceous thin bedded limestone." 1 Here the 

 limestone facies is beginning to appear. It increases in amount south- 

 wards and in the Mariscal Mountains the bulk of the formation is lime- 

 stone. On the other hand, at Cerro de Muleros, Bose's subdivision 6, rep- 

 resenting Weno and Pawpaw, is a marl with sand and lime, and his sub- 

 division 7, representing the Mainstreet is sandstone. The lithological va- 

 riations of the Weno and Pawpaw are summarized on page 27. The 

 Georgetown, like the Buda, is over much of West Texas a fine grained 

 crystalline semi-lithographic limestone, grading northwards into a marlier 

 and sandier near shore phase. The same correlation as in Central Texas 

 (page 40) holds for these strata. 



The age of subdivision 6 of Cerro de Muleros is delimited by several of 

 its fossils. The following fossils have not been found below this subdi- 

 vision, nor below the Denton formation in North Texas : Ostrea quadri- 

 plicata Shumard, Ostrea marcoui Bose. Pinna guadalupae Bose is un- 

 known below subdivision 6 and below the Weno of North Texas. Enallas- 

 ter bravoensis Bose, known from subdivisions 5-6, is not known to occur 

 lower than the Denton formation* elsewhere. Helicoctyptus mexicanus 

 Bose of subdivision 6 is as yet known only from the Pawpaw of North 

 Texas, and the same is true of Placosmilia spp., which are probably iden- 

 tical with P. bravoensis and P. mexicana. The zone of extreme abundance 

 of Gryphea washitaensis Hill so conspicuous in this subdivision is paral- 

 leled in North Texas only by that at the top. of the Denton formation. 



'Roberts and Nash: Univ. Texas Bull. 1803, pp. 14-15. 



