100 CARBONIFEROUS FORMATIONS AND FAUNAS OF COLORADO. 



LiiKjuh-pix sp. '. An eloiiyate form allied to L. pinnBeformiis of the Potsdam 

 sandstone of Wisconsin. 



From red calcareous sandstones, alternating with white limestone, 105 to 122 feet 

 above the Archean. 



(jilytoL'istites (?). Single plates. Cyrtolites. 



Lingula sp. undet. ; probably new. Orthoceras sp. undet. ; probably new. 



Orthis desmopleura Meek. Bathyurus simillinius Walcott (?). 

 Metoptoma new sp. 



These formations probably represent the Cambrian b(ids and Manitou limestone 

 of the Pikes Peak folio. 



For the same reason that the discussion of the geology of the Front Range area 

 was introduced with the Pikes Peak folio, I will prefer the consideration of the 

 Denver Basin monograph to accounts which preceded it in point of time. 



In 1S96 appeared Monograph XVII of the United States Geological Survey', b}' 

 Emmons, Cross, and Eldridge, describing the geologj^ of the Denver Basin. The 

 map of areal geology shows what may be taken as the limits of this area. It is 

 bounded on the south by parallel 39*^ 30', its northern boundary being 3 or 4 miles 

 north of the fortieth parallel. Its eastern boundar}' is about an equal distance east 

 of longitude 104° 40', and its western, the edge of the Archean mass of the Rocky 

 Mountains, or approximate!}^ meridian 105'-' 20' west. The oldest sedimentaries 

 recognized are the Rocky Mountain Red Beds, which are described as the Wyoming 

 formation. This consists of brilliant red conglomerates, sandstones, and shales, 

 with thin limestones and g3fpsum in the upper part. The thickness exposed in the 

 Denver Basin varies from 500 to 3,000 feet, but is generally somewhat imder 1,500 

 feet. The A^ariation, which relates chiefij^ to the lower beds, is accounted for as 

 being due to the unevenness of the ancient floor upon which the formations were 

 laid down. 



"The formation is separable about midway into a lower division of soft, friable 

 conglomerates and coarse sandstones with fine shale, and an upper one of shales, with 

 some prominent sandstone bands, narrow beds of limestone, and small local deposits 

 of gypsum."' (Page 52.) 



The lower Wyoming has below a mass, chiefl}^ red sandstone and conglomerate, 

 with a normal thickness of 1,200 feet, while the upper portion consists of the 

 "creamy sandstone" 200 to 400 feet thick. The upper Wj^oming contains in its 

 lower half bright brick-red arenaceous shales and sandstone, with important inter- 

 calations of limestone. The strata above the limestone become more and more 

 arenaceous, though still retaining in large degree their shaly nature. 



"At 150 or 200 feet below the top of the Trias the strata become more clayej' 

 and take on a varietj^ of irregularly distributed bright color.s — gray, yellow, green. 



