EESTJME OF LITEKATUEE. 71 



The Parting quartzite was not recognized as a distinct formation in the Crested 

 Butte quadrangle, but seems to be represented there in the upper part of the Yule 

 formation. Spurr states:-' '"Mr. Eldridge has described what is also evidently the 

 equivalent of these beds in the Crested Butte area thus: The upper division, 60 to 90 

 feet thick, consists mainly of green, yellow, red, and white shales, with more or less 

 arenaceous and calcareous layers, the latter passing into thin limestones. The per- 

 sistence of its general lithologic character renders this horizon easilj^'recognizable." 



The Leadville limestone is proportionally much thicker in the Crested Butte 

 quadrangle than at Asj^en, while the Weber formation is, on the other hand, much 

 thinner. The Maroon formation is about the same in each, being a little thicker in 

 the Crested Butte quadrangle. It is possible that the discrimination between the 

 Weber and Maroon formations was not made at precisely the same horizon in the 

 two areas, and at all events the combined thickness of these formations is in close 

 agreement, being 5,000 feet near Aspen and from rt,600 to 5,060 feet in the Crested 

 Butte cjuadrangle. 



Spurr seems to feel satisfied that the beds which he calls Gunnison formation in 

 the Aspen district are the equivalent of those bearing the same name in the Crested 

 Butte quadrangle. The described character and occurrence of the two series tend 

 to corroborate this view. A similar probability surrounds the correlation of the 

 Maroon formation in the two areas. In the Crested Butte quadrangle the Maroon 

 conglomerate is suct'eeded by the Gunnison formation with an unconformity between. 

 In the Aspen region, however, beds having the character of the Maroon pass upward 

 without apparent break into a series otherwise somewhat similar in character, but 

 colored a brighter red. It is this formation which at Aspen is followed by the Gun- 

 nison preceded by its unconformity, as in the Crested Butte quadrangle. It seems 

 from this that we have at Aspen a series of considerable thickness which is not rep- 

 resented in the Crested Butte region, a fact to which Spurr calls attention.' Its 

 absence in the Crested Butte quadrangle can hardly be accounted for in any other 

 way as satisfactorilj- as by ascribing the conditions there prevailing to the uncon- 

 formity owing to which the Gunnison formation in that area, we are told, rests some- 

 times upon the Maroon conglomerate and in some cases upon older formations. It 

 is possible, however, that this series may actually' occur in the Crested Butte region, 

 but so changed by metamorphism as to be unrecognizable. In the southern part of 

 the region, however, where the upper portion of the Maroon is thinner and has not 

 been altered, its absence is nearly certain. 



Aside from the Anthracite-Crested Butte folio, but little has been written about 

 the geology of the Elk Mountains which closely concerns the subject in hand. 



Perhaps the earliest account of geologic exploration in this region was that pub- 



aU. S. Geol. Surv., Mon., vol. 31, 1898, p. 20. Mbid., p. 38. 



