THE GLACIAL LAKE MISSOULA^ 



J. T. PARDEE 

 U. S. Geological Survey, Washington, D. C. 



The object of this paper is to show that in comparatively recent 

 time an ice-dammed lake filled a large part of the drainage basin of 

 the Clark Fork in northwestern Montana. 



To prove the existence of the lake is set forth what evidence has 

 been found in the literature of this region together with a contribution 

 by the writer, whose observations, made at odd times during the 

 past decade, were confined mainly to the Missoula and Bitter Root 

 valleys. 



Belief that the lake was ice-dammed was sugggested by certain of 

 the phenomena of this area, but is based mainly on information derived 

 from the writings of others, from which also the probable location of 

 the dam is determinable. 



The writer is indebted to Mr. F. C. Calkins, of the United States 

 Geological Survey, for suggestions and criticism. 



As long ago as 1885 Professor Chamberlin^ noted a curious phe- 

 nomenon in the Flathead lake region that he aptly describes as " sl series 

 of parallel watermarks of the nature of exceptionally slight terraces 

 sweeping around the sides of the valley and encircling the isolated 

 hills within it, like gigantic musical staves." 



In the vicinity of Missoula similar phenomena have been observed 

 by Professor Salisbury^ and are noted by Douglass-^ who mentions that 

 "in the Missoula and Bitter Root valleys on the mountain sides and 

 along the foothills are level lines or small terraces, evidently shore- 

 lines, formed by the dashing of the waves"; and a brief reference to 



1 Published by permission of the Director of the United States Geological Survey . 



2 T. C. Chamberlin, "Administrative Report," U. S. Geological Survey, Seventh 

 Ann. Kept., 1885-86, 78. 



3 Personal communication. 



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

 Montana University, 1899, 10, 11. 



376 



