732 TRANS-PECOS TEXAS. 



These sands mark periods of quite long continued shallow water during 

 their deposition. Two hundred and fifty feet above the base of the middle 

 quartzitic sand there is forty feet of massive gritty sandstone, with much 

 coarse siliceous pebbles. No organic remains were found in the sand. 



The middle alternating horizon is composed of a thin band of calcareous 

 sandstone with limestone conglomerate, and a horizon four hundred and 

 twenty feet thick of sandstone, with ledges of calcareous sandstone ending in 

 a narrow band of limestone conglomerate. 



The upper alternating horizon has thin bands, ten to fifteen feet thick, of 

 flaggy argillaceous red to bluish-yellow marble alternating with thick bands, 

 fifty to sixty feet thick, of flaggy gray and brown quartzitic sandstone. 



The final alternating horizon succeeds the upper quartzitic horizon with 

 about thirty-five feet of flaggy pale yellow marble and twenty-five feet of 

 calcareous sandstone, between which one hundred feet of rock is concealed 

 by basin debris. .The calcareous sandstone disappears beneath the basin 

 debris, dipping to the southwest. This debris, that everywhere prevails in 

 valleys, conceals higher rocks. 



No evidence was obtained that would throw positive light upon the division 

 to which this bed belongs except the superposition of the strata. The pres- 

 ence of such extensive beds of sand points to long continued shore lines near 

 at hand. 



Occurrence. — The only known occurrence of the Mountain series is along 

 Quitman Mountain from Quitman Pass southward to the Rio Grande. By 

 the succession of the rocks it occurs in the basin between Devil's Ridge and 

 Quitman Mountain, but basin debris has concealed it, probably hundreds of 

 feet below the surface. 



II. UPPER CRETACEOUS SERIES. 



1. Eagle Ford Shale or Benton Division. 



2. Lower Cross Timber or Dakota Division. 



There are certain rocks at the top of the Carpenter Spring section, on the 

 east side of Eagle Mountain, which may be classed in the Upper Cretaceous 

 series. They consist of a series of fissile, black, slightly arenaceous shale, 

 flaggy siliceous shale, siliceous limestone, and cream-colored calcareous clay 

 shale, in all making about eleven hundred feet of strata. 



Intrusive and eruptive porphyry of Eagle Mountain has so disturbed the 

 rock at the contact with the underlying Lower Cretaceous rock that the pos- 

 sible conformity could not be told. 



These rocks are placed in the Upper Cretaceous series principally by num- 

 erous Inocerami in the shale and an oyster in the siliceous limestone, that are 



