380 E. T. DUMBLE — CRETACEOUS OF TEXAS AND MEXICO. 



containing a Gryphxa in considerable numbers. This occurrence has its 

 only analogue in a band of Exogyra fexana, Roem., which occurs in the 

 upper portion of the Caprina limestone on Barton creek, near Austin. 

 Near the top of the Caprina limestone, and above the last bed of Caprina 

 observed in this division, a bed of sponges was found. The only similar 

 occurrence with wnich I am acquainted is in the Double Mountain sec- 

 tion, and there the fossils are not so clearly distinguishable. The total 

 thickness of the Caprina, as given by barometric readings, was 650 feet, 

 but it may be found still thicker at other places in the mountains. 



Capri7ia crassifibra as a Criterion of Fredericksburg Age. — While the pres- 

 ence of Caprina crassifibra cannot be taken as conclusive evidence of the 

 Fredericksburg age of the beds in which it is found, since this fossil also 

 occurs abundantly in the Washita, yet in this instance the character of 

 the rocks of the two divisions is so different that there is little danger 

 of mistaking one for the other, the Fredericksburg being much darker in 

 color and more highly metamorphosed than the Washita, which here 

 seems to rest upon it unconformably. 



The Kent Locality. — The Caprina limestone was not found at Kent, the 

 only member of the Fredericksburg which was positively identified being 

 the Exogyra texana, with such fossils as Ostrea crenulhnargo, Roem. ; Gry- 

 phasa pitcher i, Mort. ; Exogyra texana, Roem. ; Schloenbachia peruvianus, von 

 Buch. Whether the absence of the Caprina was due to the overlapping 

 of later beds or to erosion prior to their deposition is not known, but it 

 is probably due to the latter cause. 



WASHITA DIVISION. 



In the Trans-Pecos Area. — This division, which in the Colorado River 

 section attains a maximum thickness of 320 feet, finds in the Trans-Pecos 

 area a far greater development, reaching a thickness of nearly 6,000 feet in 

 El Paso county. Here, too, it gives evidence throughout its whole extent 

 of being a deposit laid down in comparatively shallow water on a gradu- 

 ally subsiding sea-bottom. 



At the Kent Locality. — At no place is this gradual subsidence more 

 plainly shown than around Kent, where the Fredericksburg and Bosque 

 divisions were evidently subjected to considerable erosion and some dis- 

 turbance prior to the deposition of the Washita, and we find the lower 

 beds of the Washita resting upon the Fredericksburg, while the higher 

 beds overlap farther and farther on the Bosque sands. The rocks here 

 are principally clays, marls and marly limestones ; but in the beds of this 

 division on the northwest side of Gomez peak a bed of limestone was 

 observed containing a considerable quantity of silicious pebbles. The 

 fossils are very abundant and well preserved. 



