L'Od CARBONIFEROUS FORMATIONS AND FAUNAS OF COLORADO. 



of tlic Ivocky Moiiiilain pro\ iiirc, and wliicli cuiTies Ti-iassic \i'rtol)ratcs. If, how- 

 (>\('r. tin- pah-ontoloyic cN-kU'iicc procluced by Knight and by l)art()n, wbicli is by no 

 means unassailablo, be admitted, it is evident that the two series are not the same. 

 However, it has alreadj' been remarked that the Wyoming beds appear to be absent 

 in the Crested Butte quadrangle and generally over the southern end of the Elk 

 Mountains, the Mosquito Range, and the Sangre de Cristo Kange, so that its absence 

 in the San fluan is not unanticipated; vrhile that area is geograptical Ij' so related 

 to the Colorado Canyon and Uinta Mountains, where Triassic beds are found, that 

 the presence there of the Triassic need not be an objection, even if the series is 

 absent over the rest of the State, as it must be if the Wyoming beds are really 

 Carboniferous. 



On the whole, however, the evidence seems to me stronger that the "Red 

 Beds" of Colorado are reallj^ Triassic, and represent the Shinarump, Vermilion, and 

 White Cliff groups of the Uinta section, or parts of them. The appai-ent absence 

 elsewhere in Colorado of the "Upper Coal Measures" of the latter area can be 

 accounted for in another way. 



if the Maroon formation represents the upper portion of the Uinta sandstone 

 and the Wyoming formation the Triassic of the Uinta Mountain section, where the 

 Wyoming beds rests upon the Maroon, as in the Leadville and Tenmile districts, or 

 when the Jurassic occupies a similar position, as it does in the Crested Butte district, 

 it is evident that the Upper Coal Measure series of King must be absent. Many 

 observers agree that the Wyoming formation succeeds the Maroon in apparently a 

 perfectljr continuous manner, and the same with their supposed coiTelates in different 

 parts of the State. Yet along the Front Range and in southwestern Colorado the 

 supposed Triassic series overlaps upon the Archean and indicates important isostatic 

 readjustments in which the conduct of the strata in northwestern Colorado may find 

 a rational explanation. Furthermore, the faunal break in the San Juan region 

 between the Rico and Dolores, in which Permian and probably portions of Carbon- 

 iferous and Triassic time are apparently missing, together with the variability seem- 

 ing to exist, such that the upper division of the Maroon formation, 2, .500 feet thick 

 in the Crested Butte quadrangle, is reduced to 300 feet (Rico formation) in the San 

 Juan region and is entirelj^ absent in the Dolores River region, are indications of an 

 uncomformity, or at least of vevy abnormal conditions of deposition. There is some 

 evidence, however, that the Upper Coal Measure series is represented in Colorado. 

 Both the fauna itself, while no correlation can be based upon it, and the lithologic 

 association with reddish sandy limestones and white sandstone of the fossils cited 

 by King from Ute Peak, in the eastern end of the Uinta Mountains, are suggestive of 

 the fossiliferous horizons in the Red Beds as they occur on the flanks of the Front 

 Range, just north of the Colorado line. The similarity in a general vfny of the fauna 



