CHAPTER VI. 

 GEOLOGY OF THE SOUTHERN END OF THE SNOWY RANGE. 



By Walter Harvey Weed. 



GENERAL DESCRIPTION. 



The northeastern' part of the Yellowstone Park embraces a small por- 

 tion of the great range of mountains which extend northward to the low- 

 lands of the Yellowstone River, a chain known as the Snowy Range. 

 Within the limits of the Park only the extreme southern end of the range 

 occurs, the much accidented and rugged country to the southeast con- 

 necting these mountains with the northern part of the eastern mountain 

 range of the Park. The eroded sedimentary rocks of this area are con- 

 tinned beneath the great accumulations of volcanic materials which have 

 been heaped up to form the Absaroka Range. 



The Snowy Mountains constitute the western portion of a high moun- 

 tainous tract which includes the great peaks of the Beartooth Range, the 

 highest mountains of Montana. This mountainous area is terminated on 

 the west by the broad mountain valley of the Yellowstone River, the 

 region being divided by the deep valley of the Bowlder River into two 

 parts, of which the westernmost, between the Bowlder and Yellowstone 

 valleys, forms the Snowy Range proper. The general structure of this 

 entire mountain tract is that of a broad anticlinal uplift, the central portion 

 of which has been denuded of its former covering of sedimentary rocks 

 and variously modified by faulting, especially at the southwestern end, near 

 the Yellowstone Park. The greater part of the region shows the core of 

 crystalline schists, gneisses, and granite which form the central plateaus. 



The central portion of the mountains is a broad, flat-topped mass, whose 

 surface constitutes a plateau 10,000 feet above sea level, deeply cut by 

 canyons 3,000 to 4,000 feet deep. Above this plateau the peaks rise a 



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