GEOLOGY OF THE LARAMIE PLAINS 



nearly 1 ,000 feet, with some gypsum outcrops in front. Gypsum 

 occurs in the Jurassic, but not so abundantly as in the Trias, 

 and only in thin layers, the thickest being two feet. 



"The Jura beds are more shaly, with some limestone layers, 

 while the Trias is essentially sandy." 



Hayden, in his report for 1870, speaks of a fine exhibition 

 of Mesozoic resting on the red syenite on Big Laramie River, 

 35 miles southwest of Fort Sanders, and for 20 to 30 miles 

 from its source the Laramie flows in a synclinal valley, the red 

 beds dipping on each side. 



In Hayden 's report, 1873, A. R. Marvin, U. S. Geo- 

 logical Survey, speaks of the Trias as coarse grits and 

 moderately coarse sandstone with sometimes fine examples 

 of cross-bedding, and with conglomerates near the base. 

 A dark red color prevails. When uptilted and eroded they 

 form curious forms, as in the Garden of the Gods and Red 

 Buttes. The Jurassic forms a narrow zone in Colorado; north- 

 wardly it increases in width. 



In the "Geology of the 40th Parallel," all the Cretaceous, 

 from the Dakota to the Fox Hills inclusive, are spoken as of 

 being well developed near the mountains, and are thus esti- 

 mated: 



Laramie — 1,500 feet. 



Fox Hills— 1,500 feet. 



Colorado, including Fort Benton, Niobrara and Pierre — 

 1 ,000 feet. 



Dakota 300 feet. 



The base of the Dakota is fine grained, passing into a brown 

 sandstone. 



In Hayden's report for 1874, he states that the Dakota 

 forms the "hog-back" of the front range and is from 200 to 400 



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