19(> CARHONIFKKOIIS KORMATIONS AND FAUNAS oK COLORADO. 



ha\i' iiiiilcil witli it, is nci'v iiuicli lliickcr than the I lei'iiio.sa roriiiatiou. This may 

 1)1" duo to the rciHin'iiizcil iiiicourofinity hy which the Hernio.sa (or the Hermosa phis 

 tho Mohis formation) was procedod, l)ut it may r(>siilt from an unconformity by 

 which I suspect it was followed. The sharp faunal l)reak between the Hermosa and 

 the Kico formations sugj>-ests an unrepresenied time interval between them. This 

 fact, the greatly increased thickness in the Dolores Kiver region, and the fauna from 

 the upper beds there, which is unlike that of the Eico and still different from that of 

 the Hermosa. all favor the hypothesis, if not of an unconformity between the 

 authentic Hermosa and Kico formations, at least of a period of nondepositiou during 

 which, in areas adjacent, as in the Dolores River region, sedimentation was going on. 

 The possibility of the Rico being represented by the series referred by Peale to the 

 Carboniferous is so remote, from the evidence at hand, as to need no discussion. 



The fact that the upper portion of the "Permian" is described by Peale as 

 overlapping upon the Ai'chean serves as a Warrant at the same time for subdividing 

 the beds grouped by him and for correlating the upper portion with the "' Triassic" 

 Red Beds overlapping elsewhere in Colorado. 



Compared with the Crested Butte section, Peale's Upper Carboniferous seems to 

 equal the lower member of the Maroon conglomei'ate, the upper member of which 

 may have no equivalent in the Dolores River region. Almost the same difficulties 

 here arise as in the suggested correlation with the San Juan Carboniferous, and the 

 same facts must be used to meet them, though their application rests upon the 

 correctness of my correlation of the upper and lower Maroon with the Rico and 

 Hermosa formations, respectively. If the Dolores Carboniferous equals both 

 the lower and upper Maroon, wholly or in part, my correlation of the Maroon 

 with the Rico and Hermosa formations will probably be in error, the slender 

 evidence at hand for the correlation of the Dolores and Crested Butte areas will 

 have been misinterpreted, and the lithologic character of the Maroon will have 

 proved very variable, but its general thickness more constant. 



In addition it must be pointed out that while the upper Maroon seems to be 

 absent in the Dolores River region, the Red Beds of the latter (including most of 

 Peale's Permian and most of his Trias) are wanting in the Crested Butte region. 

 Peale's Jurassic, with probably the upper members of his Triassic, are the equiva- 

 lent of the Gunnison formation, and while they show somewhat reduced dimensions 

 in Peale's area, the discrepancy is not so great as when compared with the equivalent 

 formations in the San Juan region. 



The geology of the Uinta Mountains is described chiefly in two reports, one by 

 Emmons, the other bj^ Powell. King also recapitulated and rearranged Emmons's 

 account in his general geologic discussion of the area covered by the survey' under 

 his charge. Powell's survey was conducted along the Green and Colorado rivers; 



