132 



CRETACEOUS ROCKS OF TEXAS. 



The foregoing rock sheets can be briefly summarized in a convenient table 

 for reference as follows: 



PROGRESS SECTION ILLUSTRATING THE CRETACEOUS SYSTEM OP TEXAS AS INVESTIGATED TO 



JANUARY 1, 1890. 



B. 



The Upper or Black Prairie Series. 



DIVISIONS. 



BEDS. 



HOEIZONS OF CHAEACTEE- 

 ISTIC FOSSILS. 



TYPICAL OCCUEEENCE. 



5. Glauconitic 



Division. 





Exogyra costatas. 

 Ostrea vesicularis. 

 0. larva. 



Mostly covered by tertiary 

 overlap. Found in An- 

 derson and Bowie coun- 

 ties. Most fully devel- 

 oped in Navarro and 

 Kaufman counties. 



4. Exogyra Pon- 

 derosa Marls, 

 or Blue Bluffs 

 Division. 



Navarro - Webberville beds 

 with arenaceous concre- 

 cretions. 



Beginning of E. costata. 



E. Ponderosa, sub-costate 

 var. 



Culmination of E. Ponderosa, 

 Rcem. 



Main or eastern portion 

 of the Black Waxy 

 Prairie area of Texas, 

 seen in Colorado section 

 from Montopolis bridge 

 to Webberville, especi- 

 ally at Blue Bluffs of 

 Colorado. 



Walnut Creek, Travis Co. 



3. "White rock" 

 or Austin-Dal- 

 las Chalk Di- 

 vision. 





Hemiaster texanus. 

 Inoceramus. 



In eastern portion of Aus- 

 tin, underlying all the 

 chalky portion of city. 

 Also at Waco, San An- 

 tonio, Dallas.McKinney 

 and Sherman. 



2. Eagle Ford 

 Clays (Shales). 



Upper Calcareous Clays. 



Lower blue clays, with giant 

 nodules. 



0. Bellaplicata, Shum. 

 Hofliles (deshayeif). 



Minor Black Prairie or 

 Mountain Creek Prairie, 

 lying between white 

 rock scarp and Lower 

 Cross Timbers. 



1. Lower Cross 

 Timber Sands.t 







Coincident with extent of 

 Lower Cross Timbers 

 south of Grayson Co. 



t Missing in Colorado River Section. 



