178 OAJiHONlFKUOUS FOKMATIUNS AND KAUNAS OF OOLOKADO. 



t\w Wobor t'oriuatioii " corresponds in a [rcnoral way to the Weber (juartzitc of the 

 Wasatch JMouiilaiii section and to the Lower Aubrey of the Cok)rado Canyon 

 section" (Tenniili' I'olio.) 1 iiavo elsewhere stated more fully jny own tentative; 

 (■(ii'rcialion of these beds. The Weber grits, together witii the Maroon formation, 

 as detined by Enuuons, which he seems to exclude from the correlations expi'essed 

 above, I would assign to the Uinta sandstone, which Emmons at an earlier date 

 correlated with the Weber quartzite. According to my view the Aubrey sandstone 

 is stratigraphically above the horizon of the AVebcr quartzite and its equivalents. 



The corresponding beds in the Leadville district bear the names of Weber shale, 

 ^^''el)cr grits, and Upper Coal Measures. The Weber grits are extremely variable 

 in iithologic character and thickness, consisting of argillaceous and calcareous shales 

 alternating with quartzitic sandstones. Impure limestones are sometimes developed, 

 and they are abundantly fossiliferous. A large fauna of Upper Carboniferous 

 species is cited in the Leadville monograph. The Weber grits, whose upper and 

 lower limits are not sharply defined, have a thickness of 2,500 feet, and consist 

 mainly of coarse sandstones, passing into conglomerates. The typical rock is a coai'se 

 white sandstone. A small Upper Carboniferous fauna is cited from a tolerably pure 

 limestone occurring near the middle of the formation. The Upper Coal Measures 

 are like the Weber grits, but in the Mosquito Range contain more calcareous and 

 argillaceous beds (Tenmile folio). They consist of alternating calcareous and siliceous 

 beds, the latter not being distinguishable from those of the W^eber grits at the base, 

 but passing upward into reddish sandstones, which in their turn are sometimes 

 difficult to distinguish from the overlying red sandstones of the Trias. The lower 

 limit is taken at the Robinson limestone. The calcareous beds below the Robinson 

 are all more or less dolomitic, while the Robinson limestone itself is a pure limestone. 

 The upper sandstones of this group are distinguished from the overlying Triassic 

 beds by a deeper color, approaching a Venetian red, whereas in the latter the color 

 is rather of a light brick red. A large fauna of Coal Measure type is known from 

 this horizon. The corresponding formations in the Tenmile folio, which have already 

 been briefly described, are too obvious to require special citation. In lithology and 

 thickness thei"e is a close correspondence. 



In the South Park region south of the Leadville district the Maroon formation 

 seems to be continuouslj^ present, and still further to the south it forms the mass of 

 the Sangre de Cristo Range in Colorado. Its occurrences in this area have been 

 described in a cursory manner by Stevenson and also by Endlich and Peale, but no 

 detailed sections are given. It was in this connection that Endlich used the name 

 Arkansas sandstone. 



While the persistence of the Leadville limestone has caused it to be often men- 

 tioned by those who have written of the geology of Colorado, the Maroon formation 



