GLA CIA TION IN THE BIGHORN MO UNTAINS 2 I 7 



Existi7ig glaciers. — Five small glaciers, all less than \y(^ miles 

 in length, still exist in the mountains in the vicinity of Cloud 

 peak at elevations exceeding 11,200 feet. In view of the fact 

 that the annual snowfall is not great, while the altitude of the 

 range is moderate, the highest point having an altitude of 13,165 

 feet, the persistence of these glaciers is probably due primarily 

 to th^ exceptionally deep and narrow cirques in which they are 

 situated, and by whose precipitous walls they are partially shel- 

 tered from the sun, and from desiccating winds. 



Drift of the last glacial epoch.— The work of the latest series of 

 glaciers in the Bighorns was similar to that which has been 

 described from other ranges in the western mountains. They 

 affected a tract about 45 miles long and 20 miles wide, extend- 

 ing from the head of the South Fork of Tongue river on the 

 north to the head of the southernmost tributary of Clear creek 

 on the south. The glaciers were, for the most part, of the simple 

 valley type, though in many cases the glaciers of several tribu- 

 tary valleys united into one, in the main valley below. Nowhere 

 was there a well-developed ice-cap, though the expanse of ice in 

 some of the valleys was considerable. In length the glaciers 

 varied from i to 14 miles, and the largest of them crossed the 

 plateau above which the sharper part of the range rises, but in 

 no case did they reach the plains beyond. 



The altitude necessary for the development of glaciers was 

 rather more than 10,000 feet in most of the valleys, but one gla- 

 cier (South Fork of Tongue river) was developed at an elevation 

 of little more than 9,000 feet. In this case there was a favor- 

 able catchment basin on a north slope, protected against warm, 

 drying winds. 



About forty-five well-developed cirques are shown on the 

 Cloud peak quadrangle. All of them were occupied by glaciers 

 of the last glacial epoch, and all but two of the late Pleistocene 

 glaciers had their sources in cirques, and were concerned in their 

 formation. The exceptions were the feeble tongues of ice at 

 Dome lake, and at the head of the South Fork of Tongue 

 river. 



Not counting the small feeders of larger glaciers, the deposits 



