THE GLACIAL LAKE MISSOULA 381 



Creek, and elsewhere in the eastern half of the Bitter Root Valley 

 but in no case at a greater elevation than that recorded. 



These bowlders are clearly seen to be erratics, not only from their 

 haphazard distribution, but from the fact that their parent rock is not 

 to" be found anywhere in their vicinity nor even in the mountains 

 that form the valley's eastern wall from Skalkaho Creek north. 



A strikingly similar rock is, however, the prevailing type of the 

 opposite Bitter Root range.' 



South of Hamilton in front of the canyons of Lost Horse, Rock, 

 and other creeks heading in this range, moraines extending down to 

 4,000 feet elevation are found, ^ It is perhaps needless to add that 

 elsewhere the Bitter Root Valley has not been glaciated. 



The foregoing phenomena as a whole seem explainable only as 

 the records of an extinct lake or sea. The old "buffalo trails" are 

 the existing remnants of its wave terraces. Its high level was approxi- 

 mately 4,200 feet above sea. At this stage the site of the present city of 

 Missoula was 1,000 feet under water, and glaciers from the Bitter 

 Root range south of Hamilton reached the lake, setting bowlder- 

 laden icebergs afloat upon it. One of these bergs grounded on the 

 prominent cape formed by the Cowell buttes. 



During the lake's halt at this level its waves worked considerable 

 fine material into the head of the small bay or cove between the 

 buttes, the remnant of which is still to be found in the upper course 

 of the ravine descending from the saddle. Sediments that settled 

 from this lake are believed to be the main source of the soil referred 

 to on p. 378, to which the agricultural value of the "bench lands" is 

 due. The gravel fiats observed by Mr. Calkins in some tributary 

 valleys of the Clark I ork are explainable as delta deposits in a lake. 

 The lake receded gradually, recording many brief halts and a com- 

 paratively long one at 3,700 feet. 



Douglass^ suggests "that the water cut with comparative rapidity 

 through its barrier in geologically recent times." 



I Waldemar Lindgren, "A Geological Reconnaissance across the Bitter Root 

 Range and Clearwater Mountains in Montana and Idaho," Professional Paper, U. S. 

 Geol. Survey, No. 27, 42-47. 



= Ihid., 51-55, and Plates I and X. 



3 Earl Douglass, The Neocene Lake Beds of Western Montana, published by 

 Montana University, 1899, 11. 



