THE OAliUUMlKJfOL.S AUD THE IGNEOUS TEAKS. 129 



boon tunied up, and its limostonos, unchanged, are found resting upon the 

 Potsdam, and standing in phices in a nearly vertical position. The change 

 from the normal horizontal position is sudden, and a few hundred feet 

 away they lie so nearly flat as to give no evidence of their near proximity 

 to a great cone of eruptive rock. 



In a similar manner the Carboniferous is found encircling the volcanic 

 peak or ridge northeast of Inyan Kara, but here the underlying Potsdam 

 was not found exposed. The Carboniferous rocks are tilted at a high angle, 

 and in their elevation are conformably accompanied by the Red Beds, which 

 are represented most conspicuously by the purple limestone. This lime- 

 stone wraps the lower part of the elevation, and rises in a gentle slope 

 some distance upon its sides. Its arching uplift seems like an excrescence 

 or large bubble upon the main slope, which descends from the Carbonifer- 

 ous plateau on the east to the valley of the Red Beds. 



The only remaining outcrop of the Carboniferous is that which encir- 

 cles the Warren Peaks, forming the foothills of the Bear Lodge range. It 

 is the largest of the minor exposures, and like the other minor exposures it 

 is associated in origin with large masses of volcanic rock. 



Though geographically the peaks and elevations of the Bear Lodge 

 range appear to form a distinct system of mountains, geologically they 

 belong to the same system as the main range of the Hills. They pertain 

 to the same epoch of elevation and igneous eruption in which were formed 

 the numerous volcanic peaks of the northern end of the Hills, and they are 

 closely identified with them in the character of their rocks and in their 

 structure. They exhibit, however, a greater localization of the eruptive 

 force, and the mass of igneous matter is much greater than in any of the 

 other peaks. The Carboniferous is tilted up on every side just as it is 

 around Crow Peak, but in several places its beds have become somewhat 

 metamorphosed by proximity to the igneous rocks. In some localities the 

 trachyte is found to penetrate between its strata. The strata are also se- 

 verely dislocated, frequently in an intricate manner. 



It is greatly to be regretted that the Carboniferous of the Black Hills 

 is so loth to yield up its biological record. Consisting almost entirely of 

 limestone, it is presumably constructed of the very ruins of the life of its 

 9bh 



