GEOLOGICAL SUEVEY OF THE TEREITOEIES. 249 



region. Here the Big Horn, Yellowstone, Madison, Snake, and Green 

 EiVers liave their origin. From this mountain center a number of 

 short ranges run northward, giving direction to a number of streams,, 

 and appearing like evidences of the abortive efforts of the elevating 

 force to keep up its direct course. Along the southern border the Snow 

 Mountains — the northern extension of the Big Horn Eauge — penetrate 

 for a short distance into the Territory, compelling the Yellowstone to 

 make a grand detour in order to sweep around the northern flank. In 

 the central portion are the Belt, Judith, and High wood Mountains, 

 forming an irregular group of short and broken ranges, around whicli 

 the Missouri sweeps to the northward before entering upon its long, 

 eastward stretch. These also have a central nucleus situated in the 

 western part of Meagher County, where the Musselshell, Judith, Deep, 

 and Shields Elvers take their .rise. North of the Missouri Eiver the plain 

 is interrupted only by Bear's Paw, the Little Eockies, and occasional 

 Tetons. 



As a general thing the mountains of this section are less rugged than 

 in the Colorado group ; although here and there are sharp, angular peaks, 

 yet as a general rule, instead of the rocky, jagged sides and serrated^ 

 crests, there are smootli slopes and rounded outlines. The elevation of 

 both mountains and valleys, as will be seen from the list of elevations 

 presented below, is much less than that of the great mountain belt of 

 Colorado and Wyoming, and even that of New Mexico, Utah, and Nevada. 

 But before presenting these statistics, I would call attention to the re- 

 markable bend of the chief range at the southwest angle of the Terri- 

 tory. Traversing as it does three sides of a trapezium, it gives both to 

 the eastern and western basin the form of a ciil de sac, the one inclosing 

 the head-waters of Clark's Fork of the Columbia, and the other the trib- 

 utaries of the Jefferson. The former descends as we move to the north- 

 west, while the latter descends toward the northeast. The dividing 

 range, growing lower and lower from its entering angle, does not resume 

 its usual altitude until it approaches the northern boundary of the Ter- 

 ritory. 



The following list of elevations, chiefly along aline running east and 

 west near the middle of the Territory, will enable us to form a pretty good 

 idea of the general elevation. 



ELEVATIONS ABOYE THE LEVEL OP THE SEA. 



reet. 



Fort Union, at the mouth of the Yellowstone 2, 022 



Trading Post, on Milk Eiver. 2, 388 



Fort Benton 2^ 780 



Forks of Sun Eiver 4, 114 



Lewis and Clark^s Pass 6, 519 



Blackfoot Fork, near the mouth of Salmon Trout Creek 3, 966 



Blackfoot Fork, near its junction with Hell Gate Eiver 3, 247 



Missoula Eiver, near the mouth of St. Eegis de Borgia 2, 897 



Summit of Coeur de Alene Mountains, at Ooeur de Alene Pass . . 5, 089 



Fort Owen, in Bitter-Eoot Yalley 3, 284 



Deer Lodge City, in Deer Lodge Yalley 4, 768 



Prickly Pear Yalley, near Helena 4, 000 



Little Blackfoot, or Mullen's Pass 6, 283 



From this list we see that the western or intermontane basin reaches 

 a depression less than 3,000 feet above the level of the sea ; and that 

 the least altitudes of the eastern slope range from 4,000 to 2,022 feet 

 above the level of the sea. Comparing these with the altitudes of the 



