LAKOTA SANDSTONE 389 



the Morrison shales appear to lie on the Sundance shales, there must be 

 an intervening unconformity representing Unkpapa time. 



LAKOTA SANDSTONE 



This sandstone gives rise to the crest and upper slopes of the hogback 

 ranges forming the outer encircling rim in the Black hills. The rocks 

 are mostly hard, coarse grained, cross bedded, and massive, with part- 

 ings of shale of no great thickness. Locally there are beds of coal in 

 the lower portion of the formation, which, about Cambria and on Hay 

 creek, are mined to some extent. The thickness is usually from 200 to 

 300 feet, excepting far to the northward, where the amount diminishes 

 to 100 feet or less. The Lakota sandstone lies unconformably on the 

 Morrison shales to the north and west and on the Unkpapa sandstone, 

 where the Morrison is absent to the southeast, but without discordance 

 of dip. The amount of unconformity between the Lakota and Morrison 

 is probably very slight, or no more than is usually exhibited where 

 coarse sands have been deposited on clays. The unconformity with 

 the Unkpapa is more profound and contact usually presents consider- 

 able channeling. 



Excepting petrified wood, which is abundant, fossils are rarely found 

 in the Lakota formation. Near Buffalo gap there were found some 

 bones of a stegasaurus of advanced type, such as might be expected in 

 the early Cretaceous time. Plants of Lower Cretaceous age appear east 

 of Hot Springs and in the Hay Creek region,* and pine needles are 

 abundant in some of the coaly layers. Numerous cycads have been 

 found, notably in the southern and eastern parts of the uplift, and re- 

 cently Professor O'Harra has observed one far to the north. This geol- 

 ogist also discovered 3 miles north of Piedmont the following fossils, 

 which were determined by Dr T. A. Stanton : A new isopod crustacean, 

 probably of the family iEgidse ; an Estheria, fish scale of a gar, Lepi- 

 dosteus, and a crocodile tooth — all fresh-water forms. 



MINNEWASTE LIMESTONE 



This formation overlies the Lakota sandstone in the southern portion 

 of the uplift, with a maximum thickness of only 25 feet. It is a nearly 

 pure, light gray limestone and was not found to contain fossils. It is, 

 however, of Lower Cretaceous age, for the next succeeding formation 

 contains distinctive fossil plants. One of its most extensive exposures 

 is at the falls of Cheyenne river, which are due to a ledge of this lime- 

 stone. 



FUSON FORMATION 



This is a thin sheet of clays lying between the Lakota and Dakota sand- 



*The Lower Cretaceous of the Black Hills, by L. F. Ward, U. S. Geological Survey. Nine- 

 teenth Annual Report, pt. ii pp. 521-946. 



