26 GEOLOGY OF THE BLACK HILLS. 



The time spent in the final preparations for a start was occupied by 

 Captain Tuttle in making observations for the latitude and longitude of 

 Fort Laramie and in rating the chronometers. By his observations the 

 flagstaff on the parade ground at the post was found to be in longitude 104° 

 32' 01" and latitude 42° 12' 30". 



All preparations having been concluded the expedition started from 

 Fort Laramie on the morning of May 25 and thence striking northeast 

 to Rawhide Creek followed up fhat creek to the east side of Rawhide Butte, 

 where it turned northward past the headwaters of the Niobrara to Old 

 Woman Fork and the Cheyenne River. It followed down the valley of 

 the Cheyenne for some miles, and then took a northeasterly course to the 

 west fork of the Beaver, and entered the Hills by the east fork. 



The geology of the region between Fort Laramie and the headwaters 

 of Old Woman Fork is, with the exception of Rawhide Butte and a few 

 less prominent ridges, very similar in character to that between Cheyenne 

 and Fort Laramie. In fact it is but a continuation northward of the soft and 

 somewhat calcareous sandstones of the great Tertiary deposit that follows 

 along the eastern slope of the Rocky Mountains. 



On the Platte and the Rawhide and their numerous dry branches there 

 are sections showing from 200 to 300 feet of these beds, and to this is to 

 be added the thickness exposed in the numerous buttes and cliffs, making 

 the entire thickness of visible Tertiary rocks about 500 feet. They consist of 

 a soft, more or less incoherent sandstone, light brown, yellow, or drab in 

 color, and generally more or less calcareous, with occasional streaks and 

 concretions of impure limestone. The latter occurrence was specially noticed 

 on the Rawhide. In some of the limestone nodules fragments of bone 

 were observed, but no well-preserved fossils were procured from them. In 

 the bluffs, however, immediately adjoining Rawhide Butte, a complete jaw 

 of Oreodon was found by Captain Burt, besides numerous fragments of the 

 bones of the same animal. So far as observed, the strata occupy a nearly 

 horizontal position, and abut against, or unconformably overlie, the ridges 

 of elevation of which Rawhide Butte is the most conspicuous. 



Rawhide Butte is situated at the head of Rawhide Creek, twenty-five 

 miles north of Fort Laramie. It is a monoclinal ridge or upheaval, chiefly 



