120 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



Cibicu and Canyon creeks. The rocks of this group are usually non-fossiliferous; 

 but fossils enough were obtained (Athyris siibtillita, Productus punctatus, Spirifer 

 cameratus, Productus, and Bellerophon) to identify it as upper Carboniferous." 



The upper Carboniferous of the Zuiii Plateau was divided by Dutton^ 

 into the upper Aubrey and the lower Aubrey. 



"The lower Aubrey consists of bright-red sandstones throughout, deposited 

 usually in rather thick, and less frequently in moderately thin, layers. They 

 are much alike in all outward respects, color, texture, and grouping, and in the 

 erosional forms sculptured out of them. They are very fine grained, without 

 traces of conglomerate or coarse shingle or gravels; and having a calcareous 

 cement they weather easily and break down into very fine red sand. Fossils 

 are scarce, but may be found here and there in sufficient quantity' and distinctness 

 to identify their age. These fossils, so far as I have seen, are the same as those 

 which abound in the beds above them. 



"The Aubrey is composed largely of sandstones, but they have a very different 

 aspect from those below. In color they are yellowish-brown, and the cement, 

 instead of being calcareous, is siliceous, in fact a regular chert. * * * These sand- 

 stones are often conspicuously cross-bedded, and the silicification of the rock has 

 in no way obscured it. * * * There are several bands of these adamantine sand- 

 stones, and intercalated with them are three or four thick beds of pure limestone, 

 containing an abundance of fossils of many and characteristic species." 



{d) Conditions in Colorado. — In southwestern Colorado the uppermost 

 Pennsylvanian deposits are the Hermosa and Rico. 



The Hermosa is described by Cross and Howe^ as a series of alternating 

 limestones, sandstones, and shales having a maximum thickness of 2,000 feet. 

 In the Animas Valley the lowest third of the formation consists of green 

 sandstones and shales with some gypsiferous shales; the rest of the forma- 

 tion has layers of limestone distributed throughout; toward the southwest 

 the limestones become more important, with some beds reaching a consider- 

 able thickness. 



In the Rico district the massive limestones are abundant only in the 

 middle of the formation, the upper part being mainly black and gray shales 

 alternating with green grits and sandstones, and a few limestones. 



At Ouray the lower 300 feet are made up of thin alternating beds of 

 sandstone, shale, and a gnarly, fossiliferous limestones. 



The upper and greater part of the Hermosa consists of pink, massive 

 grits and sandstones, red sandy shales, and gnarly fossiliferous limestones. 

 The massive sandstones, which are coarse and gritty, vary from 50 to 75 

 feet in thickness and are separated from one another by the red shales and 

 thin-bedded sandstones or calcareous layers. Heavy beds of limestone 

 occur in the southwestern San Juan region, but are lacking near Ouray. 



' Button, C. E., Mount Taylor and the Zuni Plateau, U. S. Geological Survey, Sixth Annual 



Report, p. 132, 1885. 

 ^ Cross, Whitman, and Ernest Howe, Ouray Folio, U. S. Geological Survey, No. 153, p. 4, 



1907. 



