508 K. T. HILL THE COMANCHE SERIES. 



2ntcheri type, or ammonitidae and echiuodermata which appear so abundantly 

 two terranes above in the base of the Comanche Peak beds and continue 

 thence, with certain progressive variation, to the top of the Comanche series. 

 The upper beds of this terrane are especially characterized by the immense 

 numbers of abberant molluscs, such as Monopleura, Diceras, Requienla, etc., 

 which form great masses of strata. 



The upper beds of the terrane contain many deeper water beds, accom- 

 panied by a distinct marine fauna, which has never been described. Among 

 the organisms are echiuodermata and foraminiferse (especially the large, 

 strawberry-shaped Goniolina or Parkerid), together with innumerable casts 

 of pelecypoda and gasteropoda, including species of very large size, such as 

 Natica {Tylosioma pedernalis (?), Roemer) and related forms, together with 

 occasional fragments of vertebrata. This fauna of the upper beds can be 

 collected all along the western escarpment of stratification, especially in the 

 Paluxy valley at and west of Glen Rose; in the slopes of the Brazos, north 

 and south of Granbury ; along the bluffs of the Colorado and Bull creek, 

 west of the mouth of the latter steam ; and in numerous other localities south 

 of the Colorado, in Edwards, Sutton, Kerr, Uvalde, Kendall, Kimball, Blanco, 

 Gillespie, and other counties. 



The Glen Rose beds north of the Colorado-Brazos divide are exposed 

 along a narrow area occurring as a prairie strip in the heart of the upper 

 Cross-Timbers. Their first appearance northward is in the western part of 

 Wise county, and they increase iii area southward, in Parker, Hood, Erath 

 and Comanche counties. 



These beds do not occur in Indian territory, owing to the overlap of later 

 deposits, but appear in Arkansas from Ultima Thule eastward to Murfrees- 

 boro ; the limestones described in my report on Arkansas uiider the general 

 classification of the Trinity sands belonging to this terrane. In the counties 

 of southwestern Texas between the Pecos and the Colorado and south of the 

 Burnet-Llano Paleozoic region, these rocks attain a thickness of over 2,000 

 feet, and form the remnant of a great plateau from 2,000 to 3,000 feet above 

 the sea and larger in area than the states of Connecticut and Rhode Island. 

 The Guadalupe, Comal, Nueces, Frio, Medina and Devils rivers have their 

 origin in this sterile, rugged plateau, which is being rapidly base-leveled 

 and cut up into horizontally stratified buttes and mesas by the head-water 

 erosion of these streams. 



In the mountains of northern Mexico the beds again appear projecting 

 through the intervening Tertiary plain as a part of the Santa Rosa and 

 Arboles ranges, but here they are metamorphosed into a hard blue limestone 

 which has been mistaken for Silurian by some.'^ In the southern area these 



* Report on San Rafael Mines, Santa Rosa district, Mexico, bv Professor Adolphe Rock : Mobile, 

 Ala., 1876. 



