706 W. C. A'LDEN PRE-WISCONSIN GLACIAL DRIFT IN MONTANA 



sions of these valleys into the mountains have been correspondingly 

 deepened since the deposition of this drifts we must refer a considerable 

 part of the sculpturing of the mountains to Pleistocene time, for the 

 contours marking the levels of the tops of this drift extend far up toward 

 the heads of the mountain valleys, in most cases nearly or quite to the 

 cliffs below the upper cirques. 



Discussing the "Kennedy gravels," under the heading "Pleisto- 

 cene ( ?)," Mr. Willis^^ wrote in part as follows: 



"Gravels are widely spread on the highest tables of the plains north of Cut- 

 bank River and between the forlvs of Milk River. Their position suggests a 

 correlation with the Kennedy formation. On the other hand, the gravels of 

 the plains are composed chiefly of quartzite and presumably have lost the more 

 soluble constituents, which still occur in the Kennedy formation. From this 

 distinction greater antiquity -may be argued for the high-level gravels of the 

 plains. 



"Salisbury in summarizing the results of Calhoun's investigations in 1901, 

 in this region, says :" 



"The high-level quartzite gravels on the plains east of the mountains are 

 believed to be deposits made by streams at the close of the first epoch of base- 

 leveling recorded in the present topography. 



"If this belief be confirmed, the high-level gravels of the plains and the 

 Kennedy formation are alike in genesis and derivation from the Lewis Range. 

 They may, nevertheless, belong to widely different stages of uplift and erosion. 

 The characteristics of the gravels and the physiographic record of the moun- 

 tains may decide the relation on closer study." 



Inasmuch as we have shown that both the gravels on Kennedy Eidge 

 and those on a considerable part of Milk River Ridge contain glaciated 

 material, the relation to the "quartzite gravels" farther east is probably 

 somewhat different from what Mr. Willis had in mind, yet it is possible 

 that they do belong to "widely different stages of uplift and erosion." 

 A part of the "quartzite gravels" may be pre-glacial stream gravels, as 

 believed by Calhoun, and much of the dissection of the Blackfoot pene- 

 plain and the correlated deepening of the mountain valleys may have 

 been accomplished prior to the deposition of the high-level glacial drift. 

 Mr. Campbell has suggested that instead of issuing from the mountains 

 onto an undissected plain the earlier glaciers may have extended down 

 valleys already cut in the plain, though to less depth than at present, 

 and have spread laterally over the higher tracts on either side, leaving 

 the thick drift largely as lateral moraines from which outwash deposits 



" Op. cit., p. 329. 



" R, D. Salisbury: Glacial work in the western mountains in 1001. .Tournal of Ge- 

 ology, vol. ix. November-December. 1001. p. 721. [Incorrectly cited by Mr. Willis as 

 from .Januarj', 1902, number of this journal.] 



