720 TRANS-PECOS TEXAS. 



with the characteristic Exogyra arietina, and a small gryphea in great num- 

 bers. Second, the Nodosaria texana horizon, in which are millions of indi- 

 viduals of this unique foraminifera, described by Conrad from the Rio Grande 

 basin near El Paso. The form passes down into the Arietina horizon. 



Character of the Rock. — The rock is decidedly siliceous, especially that 

 of the Nodosaria texana horizon. 



The Arietina flags proper are of a compact, blue, fine-grained, slightly sili- 

 ceous limestone, with occasional thin bands of marl between the strata. 



That of the Nodosaria texana horizon occurs in thin siliceous flags, and 

 are yellowish gray to pale brick red in color. Between the Nodosaria horizon 

 and the second Caprina bed overlying there is a band of thinly-bedded pale 

 blue limestone five feet thick, which weathers in conchoidal balls. 



The Arietina bed occurs in the small hills west of Etholen Station, and be- 

 tween Quitman Mountain and the Southern Pacific Railway, and at the south- 

 ern base and on the western flank of Sierra Blanca Peak, north of the railway. 



These small hills are surrounded by the debris from the mountains near at 

 hand, and by the silt of the' lake basin that occupies the valleys. The rocks 

 of the hills on the south side of the railway nearest Quitman Mountains dip 

 northward away from the mountain, while those on the south, as well as on 

 the eastern and western flanks of Sierra Blanca Peak, dip toward the south- 

 west at nearly the same degree. By referring to the accompanying map 

 these features may be observed. 



The Nodosaria texana occurs also at the southeast side of the south end of 

 the Quitman Mountain, two miles north of the Rio Grande, where it occupies 

 a fissile, ferruginous, flaggy, calcareous sand, underlying an immense devel- 

 opment of shale. 



SECOND CAPRINA BED. 



This, the second Caprina horizon, is the first known to exist above the Ex- 

 ogyra arietina bed, which bed appears almost at the very top of the Washita 

 in the Colorado section. 



It is not in great development here, however, being only ten feet thick. 

 The only known occurrence of this bed is at the south base of Sierra Blanca 

 Peak, where it occurs as a thickly-bedded dark gray siliceous limestone that 

 weathers dull yellowish gray. 



Immediately above the Nodosaria horizon cited above, at the south end of 

 the Quitman Mountain, there is a horizon of limestone, but the Caprina was 

 not found. A fragment of a large ammonite was collected from the lime- 

 stone. 



At the south base of Sierra Blanca Peak, the point of the only known oc- 

 currence of the second Caprina horizon, the rock is completely metamor- 



