386 E. T. DUMBLE — CRETACEOUS OF TEXAS AnI^ MEXICO. 



and south, form a land-locked valley, which is further inclosed by ranges 

 on the Mexican side of the river. 



All of the sedimentary rocks which are exposed, except possibly num- 

 ber 2, belong to the Fort Pierre, but to the west are many white hills 

 which may belong either to the Colorado or Fox Hills. 



General Section. — The following is a general section from the more de- 

 tailed one made by Mr Cummins and myself. The measurements are 

 from readings of aneroid barometers and are approximately correct : 



Feet. 



1. Lava-flow ; rim rock of mountain 200-300 



2. Interbedded sandstones of various colors with calcareous clays and vol- 



canic ash 550 



3. Conglomerate, resting unconformably on 4 1- 16 



4. Lava-flow ; apparently conformable on 5 50 



5. Interbedded brown and red sands, purple shales and yellow quartzitic 



sandstone 500 



6. Gray and purple shales with thin strata of sandstone 200 



7. Coal shales with beds of laminated sands and two seams of coal ; highly 



fossiliferous between and below the coal seams 800 



8. Interbedded sands and sandstones, some highly calcareous; fossilif- 



erous. . . , 250 



9. Shales with concretions of clayey limestone containing fossils ... 175 



This gives a total thickness of over 2,800 feet. 



Fossils. — The fossils contained in numbers 7, 8 and 9 are very abun- 

 dant and well preserved. From the large collections made a suite was 

 sent Mr T. W. Stanton, of the United States Geological Survey, for deter- 

 mination. He reports the following species : 



1. Nautilus dekayi, Morton. 



2. Schloenbachia delawarensis, Morton. 



3. Schloenbachia, (?) n. sp. 



4. Baculites asper, Morton. 



5. Baculites ovatus, Say. 



6. Flacenticeras guadalupx, Roemer. 



7. Heteroceras, sp. undet. 



8. Hamites, two species, possibly new. 



9. Turitella trilira, Con, var. 



10. Strepsidura interrupta, Con. (?) 



11. Gyrodes, sp. undet., cf. G. infracarinata, Gabb. 



12. Volutomorpha, n. sp. (?) 



13. Ostrea elegantula, Newberry. 



14. Exogyra costata, Say var. This particular variety, intermediate between typical 



E. costata and E. ponderosa, occurs in the Eutaw group and in the lower part 

 of the Ripley, in Alabama, always at a lower horizon than true E. costata. 



15. Pinna, sp. undet. Resembles P. loquata, Con., of the Ripley. 



16. Inoceramus cripsi, Mantell. 



17. Trigonia thoracica, Morton. 



