GLACIATION IN THE CRAZY MOUNTAINS 561 



ber creek and Swamp creek, for moraines from these canyons overspread their 

 valley sides and combine. Possibly the north fork of Big Timber may have 

 contributed to this piedmont sheet, but the region between the two forks of 

 Big Timber was not studied. 



In his previous report on the Crazy mountains Professor Wolff estimates the 

 elevation of strife as 500 or even 1,000 feet above the present- stream beds.' 

 The observations of the present writer confirm that estimate. The elevation 

 of striae, the height of cliffed slopes along the edges of glacial troughs, and the 

 altitude at which side troughs now hang above the main trough floors go to 

 show that the main glaciers must have had a thickness of between 500 and 

 1,000 feet. 



Living Glaciers 



Glaciation in the Crazy mountains is not yet extinct. At the head of the 

 west branch of the north fork of Big Timber creek, facing to the northeast, 

 there is a small cliff glacier at an altitude of 9,000 to 9,500 feet. The length 

 of the glacier, including its snow field, is probably not more than an eighth of 

 a mile, while its width is about one-fourth of a mile, giving an area of about 

 20 acres. This glacierlet was discovered by the Harvard Summer School party 

 on July 31, 1907. The failure of previous observers to note its true character 

 was doubtless due to the fact that it is generally covered with light snow that 

 effectually conceals its structure. The general features of the glacier are 

 shown in plate .35, figure 1. In the midst of what appears to be an ordinary 

 snow patch is seen a mass of dirty ice, showing distinct banding and con- 

 tortion with shearing. Miniatui-e crevasses, extending obliquely backward 

 from near the east side, show the characteristic greenish blue color of glacier 

 ice. The morainic material seen in the foreground of plate .35, figure 1, lies 

 at least In part upon dirty, banded ice. The convex front of the ice changes 

 gradually into the concave surface of the snow field, and, at the back of the 

 latter, cracks in several places indicate the presence of the hergschrund. The 

 walls of the enclosing cirque rise sheer .500 to TOO feet to the ridges and peaks 

 above. The melting snow and ice drains into a lakelet on tlie floor of the 

 trough below. A recent letter from ]\Ir E. C. Russell, forest supervisor at Liv- 

 ingston, Montana, states that in September of this year large blocks of ice. 

 that had broken off the glacier, had fallen into this lakelet. 



Near the head of the south branch of the south fork of Sweetgrass canyon, 

 where it heads against the east fork of Cottonwood (Pine) ci'eek, there is a 

 large snowfield that is believed by the writer to conceal another small glacier. 

 This snowfield lies at an altitude of nearly 10,000 feet and faces northeast. 

 It was not visited by the party, but, seen from a distance, it presents the same 

 convexo-concave slope noted in the case of Big Timber glacier. Several cracks 

 were observed at the head of the snowfield, and an obscure oblique structure 

 running downward from west to east was noted in the snow, as if the latter 

 only partly concealed banded ice. No other snow patches seen displayed such 

 characteristics, save only that containing the Big Timber glacier. 



A third glacierlet in the head of Rock creek is reported by Forest Assistant 

 R. B. Wilson in an unpublished manuscript. He does not specify the position 

 of this glacier except by general reference. The creek lias two well defined 



s Op. cit, p. 446. 



LI — Bull. Geol. See. Am,. Vol. 19, 10O7 



