24 GEOLOGY OF THE BLACK HILLS. 



labor and care, and while, perhaps, it has not been persistently followed, 

 it is the opinion of many of those best capable of judging that though with 

 great pains hardy vegetables may be cultivated, the usual cold nights of 

 this high and dry altitude are serious drawbacks. ' Besides, it may be said 

 that grazing requires so much less labor and produces so much greater 

 returns, that agriculture offers few charms to the settler. 



From Cheyenne to Fort Laramie, and in fact northward to the South 

 Fork of the Cheyenne River, the country is underlaid by the beds of the 

 White River Miocene Tertiary, consisting of gray and yellowish sandstones 

 and sandy clays and marls. These are the deposits from the ancient Ter- 

 tiary fresh-water lake which overspread so large an area of the Great 

 Plains, and they are found to cover unconformably the truncated strata of 

 the Cretaceous, Trias, Jura, and Carboniferous. These older rocks were 

 nowhere seen on our road to Fort Laramie, as their outcrops are along the 

 immediate base of the mountains, fifteen miles to the westward, but their 

 character and occurrence have been repeatedly examined. (See Hayden's 

 report for 1870.) Frequent exposures of the composing beds of the Tertiary 

 are presented in the different valleys, and especially in the cuttings of the 

 Chugwater, while isolated ridges and buttes on the Plains indicate their 

 composition, and bear witness to the enormous thickness of material that 

 has been removed by denudation. The lowest observed rock of the Ter- 

 tiary is a heavy sandstone, sometimes locally calcareous, with occasional 

 bands of impure limestone, but more frequently arenaceous and loosely 

 aggregated, crumbling and weathering rapidly. This is best exhibited in 

 the Chugwater Valley and on the road between the Chugwater and Fort 

 Laramie. On the Chugwater it has a thickness of 150 to 250 feet, and 

 borders the creek valley on both sides like a wall, though often cut up and 

 weathered into castellated forms like those of the Bad Lands. 



Above this soft rock occurs a coarse conglomerate. This is noticeable 

 on Crow Creek south of Cheyenne, and on Lodge Pole and Horse Creeks, 

 and on the Chugwater it becomes a very prominent feature in the geology. 

 Capping the underlying soft rocks, it has protected them from rapid weath- 

 ering, and where it is wanting, the whole character of the landscape changes, 

 rounded and rolling hills taking the place of abrupt cliffs and escarpments. 



