COLORADO AND MONTANA DIVISIONS. obO 



III tlie inidille Rio Grande section they are lime flags, sei)arated by 

 thill bauds of hiniinated clays, and contain Inoceranii and fish remains. 



On Soro creek, west of Del Rio, they are also flaggy, but somewhat 

 more arenaceous as well as bituminous. Inocerami were the only fossils 

 found here. 



At this locality the contact between tlie Vola and tlie Eagle Ford beds 

 is well shown, and there seems to be absolute conformit}^ between them. 

 The Vola limestone shows no sign of erosion previous to the deposition 

 of the Eagle Ford, but stretches along as a perfectly plain surface through 

 an exposure of several hundred feet. 



Above the Washita beds, on the northeast side of Gomez peak, near 

 San Martine, there are beds of shal}^ to flaggy limestones belonging to 

 this stage. 



At only three localities have I been able to determine the presence of 

 beds equivalent to the Austin limestone. It was found well developed 

 in the middle Rio Grande section, and it was recognized at two localities 

 in the Davis or Apache mountains. One of them was a small remnantal 

 patch near Apache spring, just opposite the ranch-house of the Newman 

 brothel's. This was a bed of Gryphxa vesicularis, var. aucella, Roem., with 

 Ostrea congesta^ Con., a large Inoceramus and an unknown oyster. It was 

 also recognized near Gomez peak, at the locality mentioned above, over- 

 lying the Eagle Ford shales. 



MON TA XA DI VISION. 



Its Importance. — This division is probably the most valuable, econom- 

 ically, of all the west Texas Cretaceous, and, when the entire section is 

 made out, it may prove to have as great, if not a greater, thickness than 

 the Washita. 



Areas investigated by the Author. — The only two areas in which these 

 beds have been examined by the writer are along the middle Rio Gran I e, 

 the rocks of which were described in the paper referred to above, and a 

 district in Presidio county, lying between the Viejo or Rim Rock moun- 

 tains and the Rio Grande, which, as it includes the San Carlos coal 

 mines, will be here described as the San Carlos section. 



This area is situated twenty-eight miles by wagon road south of Chispa 

 and eight miles from the river. The valley is rendered extremely pictur- 

 esque by its bright colored rocks and the beautiful forms into which they 

 have l)een carved by the combined effects of faulting and erosion. Four 

 miles to the east of the San Carlos cam}) tlie Rim Rock or Viejo moun- 

 tains rise to a height of 2,700 feet aljove the valley, the ui)per 200 or 300 

 feet being a vertical wall of trap, witli columnar structure, in which single 

 columns of 150 feet are clearly deflned. The mountains, running north 



