THE GLACIAL LAKE MISSOULA 385 



idea of the great depth near the 49th parallel of the one that flowed 

 south through the Rocky Mountain trench may be gained from the 

 fact that here it overflowed eastward across the continental divide 

 through Ahern and other passes at the head of Belly River. ^ 



The eastern or upper Kootenai Valley held another great south- 

 flowing glacier.^ At Kalispell, about sixty-five miles south-southeast 

 from the boundary at the point just referred to, the ice was 3,000 feet 

 deep, or its surface nearly 6,000 feet above sea, and came from the 

 north-northwest.3 



This lobe, probably reinforced by that of the upper Flathead 

 Valley, flowed southward across the Flathead lake region, reaching, 

 as indicated by the observations of Professor Elrod,'^ to the Jocko 

 Valley. A deep glacier flowed south through the Purcell trench, 

 extending at least to the southern end of Lake Pend d' Oreille. -'^ At 

 the north shore of this lake, ice is shown by Calkins'" to have been 

 about 2,500 feet deep. 



The same author has also noted the glaciation of Clark Fork 

 Valley above Lake Pend d' Oreille in the vicinity of Bull River, ^ 

 and his observations, with those of Wood,^ indicate the ice to have 

 been at least 2,000 feet deep. Bull Lake trench probably supported 

 another deep ice-stream^ that may have been a branch from the 

 Purcell lobe at Bonners Ferry. There is also evidence to indicate 

 that south-flowing ice occupied the Kootenai Valley above Libby,'° 

 and also the Plains-Jennings depression." 



1 G. E. Culver, "Notes on a Little-known Region in Northwestern Montana," 

 Trans. Wis. Acad. Set., VIII (1891), 204. 



2 R. A. Daly, Can. Geol Survey, Summary Report, 1904, 95. 



3 R. D. Salisbury, "Glacial Work in the Western Mountains in 1901," Jour, of 

 Geol., IX, 724. 



4 M. J. Elrod, "The Physiography of the Flathead Lake Region," Bull. Univer- 

 sity of Montana, No. 16, 202. 



5 T. C. Chamberlin, Seventh Ann. Rept. U. S. Geol. Survey, 1888, Plate VIII, 

 178, 179, and Fig. 15; ibid., "Administrative Report," 1885-86, 78; and Bailey 

 Willis, "Changes in River Courses in Washington Territory, Due to Glaciation," 

 Bull. U. S. Geol. Survey, No. 40, 8. 



6 F. C. Calkins, op. cit., 31. ^ Ibid. 



8 H. R. Wood, "Glaciation in Western Montana," Science, XX (1902), 162. 



9 F. C. Calkins, op. cit., 31, and unpublished field notes. 



1° R. D. Salisbury, op. cit., 723, 724. " H. R. Wood, loc. cit. 



