eesump: of literature and classification of areas. 



Although I had set out to consider ouly the Carboniferous rocks and faunas of 

 Colorado, it seemed that the relations to each other of the sections situated in 

 different parts of the State could not be intelligently estimated without more or less 

 careful reference to the strata upon which the}' rest or those b}' which they are 

 succeeded. As the earlier Paleozoics play but an insignificant part in the sections 

 seen in the State, it proved a comparativelj^ easy task to carry along the entire 

 pre-Carboniferous portions of the different sections; and the supposed Trias and 

 Jura were also held in mind. 



Carboniferous rocks are usually seen in Colorado only where brought to the 

 surface b^' mountain uplifts. Otherwise the}' lie deeply buried beneath heavy 

 sections of Mesozoic and Tertiary sediments and often beneath igneous flows. 

 Their present outcrop, thei'efore, consists largel}' of more or less discontinuous 

 areas exposed along the flanks of mountain ranges or sometimes in the channels of 

 rivers. 



As exhibited on the general geologic map of the Hayden atlas," the most 

 conspicuous feature in tlie distribution of the Carboniferous is a discontinuous band 

 stretching from the northwest corner of the State to the center of its southern 

 border. This is too large a tract to be conveniently considered without subdivision, 

 especially as the geologic section is not uniform throughout. 



The northwestern portion of this band of Carboniferous outcrop is formed bj' 

 the eastern end of the Uinta Mountains; and as it is separated bj' a considerable 

 extent of Mesozoic and Tertiary beds from the remainder of the Carboniferous 

 outcrop to the southeast, it can appropriately be considered as a distinct area, under 

 the name of the Uinta Mountain region. 



Southeast of the Uinta Mountains is a large area of Carboniferous having a very 

 irregular outline, which is chiefly exposed along the White and Grand rivers and 

 their tributaries. No single topographic feature seems to be preeminently distinctive 

 of this area, but 1 have distinguished it as the Grand River region, giving it the 

 name of the river which divides it in the middle. 



Connected with this to the south, and reall}' forming a part of it, is the area 

 produced by the upturned beds of the Elk Mountains. I will, however, speak of 



aV. S. Geol. Geog. Surv. Terr., Atlas Colorado, etc., 1877. 



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