70 DESCRIPTIVE GEOLOGY. 



but they were soon abandoned, tlie lime made from the Carboniferous rocks 

 at Granite Caiion proving much more desirable. 



An analysis of the Cheyenne limestone yielded Mr. K W. Woodward 

 the following : 



Silica- 1.49 1.52 



Ferric oxide 0.37 0.31 



Manganous oxide 0.15 0.15 



Lime 54.16 54.18 



Magnesia 0.15 0.15 



Carbonic acid and water 43.68 43.69 



100.00 100.00 



North of Crow Creek, along the bluffs of Lodge Pole and Horse 

 Creeks, the beds retain much the characteristics of those already described, 

 being light-colored, fine-grained sediments, largely arenaceous, with beds 

 of marls and calcareous grits. The prevailing color of the sandstone is 

 either ash or lavender, many of the beds suggesting fine pumice. 



Near the mountains, between Lodge Pole and Chugwater Creeks, both 

 the Tertiary and Cretaceous rocks have undergone considerable erosion, 

 producing longitudinal valleys shut in by the Laramie Hills on one side 

 and abrupt walls of Pliocene Tertiary on the other. North of Horse Creek 

 these walls, which are quite regular, and have been designated as Shelter 

 Bluffs, rise from 250 to 300 feet in height. They consist of the same light- 

 colored marls as found upon Crow Creek. Li places they are filled with 

 small concretions of the same material, although harder, and carry thin beds 

 of sandstone. 



The Chugwater is, perhaps, the most characteristic valley, which cuts 

 through the Tertiary basin, the stream running for over 50 miles through 

 a nearly continuous line of bluffs, offering exposures of marls, grits, and 

 clays capped by the hard sandstones. Every few hundred yards the bluffs 

 are cut at right angles by ravines and gullies, which offer considerable 

 diversity in form and outline, suggesting the "Mauvaises Torres" of Dakota. 



All through the marls and calcareous grits, but more especially abund- 

 ant in the bluffs along the Chugwater, occur irregular segregations and 



