LOWEE CRETACEOUS. 595 



Feet. 



8. More argillaceous light-gray limestone, interstratified with dark clay shales; one of the 



limestone bands yielded Epiaster whitei, Terehratula (Kingena) wacoensis, Gryphxa washita- 

 ensis (?), Plicatula incangrua, and ScMxnbachia vespertina, and another band farther west 

 yielded Epiaster uhitei, Schlcenbachia acutocarinata, S. serratescens, and Hamitesfremonti 300 



9. Dark clays with brownish calcareous bands; Exogyra texana abundant 50 



10. Covered 100 



11. Limestone, very heavy bedded above, with increasing bands of argillaceous limestone below; 



Requienia and a small conical Foraminifera abundant; Exogyra texana also occurs 300 



12. Shales, limestones, and bands of brown sandstone, not well 'exposed 250 



13. Argillaceous limestone, with some harder bands containing "Caprina" and Requienia 75 



.14. Generally more massive limestone with some bands of brown sandstone. Also contains 



"Caprina," Ostrea, etc 350 



15. Quartzitic sandstone with thinner bands of clay shale and impure limestone, dipping steeply 



westward 400 



16. Hard, blue limestone, full of Orbitolina texana 60 



17. Sandstone and impure limestone with some clay 40 



18. Sandstones and clays 250 



19 . Thin-bedded passing into massive limestone, full of Orbitolina texana; at least 300 



The steep western surface of No. 19 forms the eastern wall of the canyon of the Rio Grande 

 at this point. 



So far there has been no apparent serious break in the section, but the beds now become 

 complexly faulted and folded. A short distance north Xo. 19 is cut off by a fault, and on the 

 west, across the river, the same bed seems to be repeated in several postures. 



It is evident that the eastern portion of the section crosses a syncline, so that in passing 

 from No. 1 to No. 5 the same beds are all crossed twice. In the rest of the section, while there 

 may be some repetition of beds due to small faults, there are no anticlines nor synclines, and 

 the fossils show that in general the beds are successively older toward the west. No. 3 is Upper 

 Cretaceous, of the age of the Fort Benton; Nos. 4 to 8 are Washita; Nos. 9 to 14, and probably 

 15, are Fredericksburg; and Nos. 16 to 19 belong to the Trinity. As the dips are all steep to 

 the west it follows that all the beds from No. 4 to No. 19, inclusive, are overturned. It will 

 be seen also that the succession of rocks and fossils is similar to that found on the east slope 

 of the mountains near Quitman Canyon, and that there is no place for the great sandstone 

 series of the "Mountain bed " within the Washita division. It must be older than the Orbitolina 

 limestone. 



H 13. CHISOS REGION, TEXAS. 



For the region lying in the grea,t bend of the Rio Grande in Brewster County, 

 Tex., the report prepared by Udden in 1905 may be consulted. He sums up as 

 follows r*""^ 



It was not attempted to make out the succession of separate divisions in the Comanche 

 series, for this would have required much more time than was at our disposal, but it may never- 

 theless be worth the while to sum up the observations made bearing on this subject. 



1. The base of the series consists of sandy or clayey beds containing calcareous material 

 also, weathering rather easily. At Cienega Mountain these strata have a thickness of about 150 

 feet. 



2. At about 150 feet above the base there is a conglomerate or a pebbly sandstone measuring 

 some 20 feet. These two members, and verj- likely a part of the succeeding beds above, are 

 absent at Altuda, where they probably never were laid down, owing to an overlap. 



3. At an unknown distance above tliis conglomerate there are some dark ledges of very 

 compact limestone interbedded with some shaly seams, and these are followed upward by 

 several hundred feet of heavy-bedded limestones of lighter color. These lowest three di-\-isions 

 are equivalents of the Presidio beds in the Shafter section. 



4. Then follow 200 or 300 feet of more thin-bedded and less pure limestones, which weather 

 more easily and contain a fauna resembling that found in the Shafter beds. 



