262 CARBONIFEROUS FORMATIONS AND FAUNAS OF COI.OKADO. 



the Crested Butte district is not iviiown, ;iikI those of th<' niidiUc ^^^■hl■l■, Robinson 

 limestone, and Maroon formation of the Leadville and Tenniile districts !ir(> very 

 imperfectly known. 



A comparison of tiic sections of these three areas without the aid of pah'on- 

 tolog-ie evidence would indicate that the Hermosa foi-mation, and possibly the Molas 

 of tlu' San Juan and the Weber and Maroon formations of the Crested Butte and 

 Leadville districts, are in a general way equivalent. The correctness of this correla- 

 tion is borne out bj' the distribution and range of species shown in tlie table. The 

 species which characterize the lower Hermosa are present in the Crested Butte and 

 Leadville districts, in the Weber formation of the one and the lower Weber or 

 Weber shale of the other. The agreement in range of individual sjiecies with that 

 in the San Juan is, as might be anticipated, somewhat greater in the case of the 

 Crested Butte district than in the Leadville district. This may be entirely due to 

 geographic separation, or it may be partly owing to a possible mixing in the Lead- 

 ville collections of specimens from different geologic horizons. The evidence for 

 suspecting that this may have occurred consists in the fact that several, and in some 

 cases a large number, of different localitj^ labels were found with single lots of 

 fossils. 



Thei-e seems to be evidence for believing that the lowest Pennsylvanian deposits 

 in the San Juan, Crested Butte, and Leadville areas were essentiall}' synchronous. 

 It also seems to be true that essentially the same fauna occui's in the Hermosa forma- 

 tion of the San Juan region, the Weber and lower Maroon formations of the Crested 

 Butte, and the Weber shale and Weber grits of the Leadville district. Of the fauna 

 of the upper Maroon in the Crested Butte district and of the Maroon in the Leadville 

 district we know nothing in one case and very little in the other. I have entertained 

 the hypothesis that the Rico formation of the San Juan region is equivalent to the 

 upper Maroon formation of the Crested Butte, but unfortunately no paleontologic 

 evidence exists to prove or disprove this conjecture, as has just been .said. The 

 Maroon formation of the Leadville district corresponds in its position in the section 

 to the upper division of the Maroon in the Crested Butte. Only one determined 

 species, Prodnctus cora, is known from the Maroon formation of the Leadville area, 

 and it occurs in both the Hermosa and Rico formations. In the Robinson limestone, 

 which is taken as the base of the Maroon formation, or as the dividing line between 

 the Maroon and Weber grits, five species are known: Spirifev roclcymontanun^ Squa- 

 mularia jjerplexa, Seminula subtilita, StrophoHtylus remex^ and jBellerophon crassus. 

 Of these, Stropkostylus remex is found in the Rico but not in the Hermosa, Seminula 

 subtilita a.nd JSellerophon crassus in both Rico and Hei'mosa, and Spirifer rorky- 

 montanus and Squamularia perplexa ow\y in the Hermosa formation. The case stands 

 then somewhat against my hypothesis, but the evidence can not be regarded as con- 



