178 A. G. Peale—Age of the Rocky Mountains in Colorado. 



we get within about five miles of the Dolores, when Upper 

 Carboniferous strata appear, with every evidence that a 

 shore line once existed there. The outcrop of Red Beds 

 resting on the granite is exposed to view continuously 

 for more than 20 miles. The fact that the Red Beds thin 

 out and disappear as we go east, and that the Jurassic does the 

 same until the Cretaceous alone rests on the granite, points to 

 the fact that the sea was gradually encroaching on the land, 

 and there must have been a subsidence here extending into 

 Cretaceous time. South of the Gunnison River are small 

 areas of Archaean rock where trachytic flows rest upon them 

 with no sedimentaries interposed, and in others the Archaean 

 rocks project through the trachyte forming isolated granite 



In South Park, on the west side as I have already said, the 

 entire series of sedimentaries from Primordial to the top of the 

 Cretaceous is present, while on the east side the Dakota group 

 rests on the granite. Prof. Stevenson acknowledges that there 

 was subsidence during the formation of the Triassic rocks, as 

 far as the Front Range is concerned. He says, (p. 500), " In 

 this region there was a subsidence during the deposition of the 

 Trias which affected the interior little,' if at nil. for over the 

 greater portion of that area the Trias is altogether wanting." 

 Again he says, (p. 490), "In South Park the Cretaceous rocks 

 rest directly upon metamorphic rocks, and are themselves more 

 or less altered. At no locality were they seen resting upon any 

 sedimentary rocks older than themselves." I have shown that 

 Triassic rocks show at more than one locality in the interior. 

 On the east side of South Park the Dakota Croup rests on the 

 granite, with shales above it containing well defined Cretaceous 

 fossils. On the west side the Dakota Group rests on Jurassic 

 shales, beneath which are the massive Red Beds of the Trias.* 



Under the head of Carboniferous, Prof. Stevenson refers to 

 exposures of coarse sandstones and siliceous limestones on the 

 "west side of the Park extending 8 miles east of the mi 

 (p. 373), and under the head of Cretaceous he says, "In South 

 Park the Cretaceous rocks occupy a synclinal trough, lying 

 east from Fair-Play, and extending from the mountains at the 

 north to very near the southern boundary of the park, (p. 389)." 

 He does notappear to have seen the Jura and Trias between 

 the Cretaceous and Carboniferous in South Park (see Reports 

 U. S. Geol. Survey for 1873), or if he did, failed to no 

 as I can find no reference to them under his heading Triassic 

 and Jurassic, (pp. 378-382.) 



In Middle Park, Mr. Marvine found the No. 1, Cretaceous 



* Report TJ. S. GeoL Survey, 1869, p. 79, and Report for 1873, pp. 38-41 



