534 FBE-WISCONSIN GLACIAL DRIFT IX MONTANA 



Badger and Blacktail creeks, where again there is an area drained by 

 streams which do not head in the mountains. 



Blackfoot Peneplain axd Cycles of Erosion 



The remnants of the high plain and the deposits thereon in the Brown- 

 ing quadrangle and adjacent northwest part of the Blackfoot quadrangle 

 are thus very significant in the interpretation of the physiographic and 

 glacial geology of the region. 



Calhoun 4 pointed out evidence of several cycles of erosion noted during 

 the course of his observations in this area. Our interpretations are some- 

 what different in details, but much the same in general. The remnants 



s>> „ ^,v -■, - ^/C 



:- — c — ^-. .jif; 



^'-.1'iL.Jfc.- 



Figure 2. — Tieic northeastward from Broicning-Baoo Stage Road on the Crest of Milk 



Biver Ridge 



Showing the relations of the second peneplain (in foreground) to a remnant of the 

 first or Blackfoot peneplain in background, i From photograph, partly diagrammatic in 

 foreground.) 



of the high-level plains in the Browning and Blackfoot quadrangles in- 

 stead of representing a single peneplain appear to represent two plains or 

 sets of plains. The name "Blackfoot." proposed by Mr. Willis for the 

 peneplain, if it is to be applied to the initial physiographic features of 

 tins part of the plains, as he indicated, should be limited to the plain rep- 

 resented by the highest and oldest surfaces on these ridges. The locations 

 and extent of these tracts are shown on plate 13. On Milk Biver Ridge 

 this peneplain includes only the higher parts of the ridge immediately 

 north of North Fork of Cutbank Creek and an isolated high plateau in 

 township 35 north, range 11 west, If miles northeast of the head of the 

 main part of the ridge. This head of the ridge is in township 33 north, 

 range 13 west, and has an elevation of 5,900 feet above tide. From the 

 flat top at this elevation a steep slope, apparently due to cutting down 



* F. H. H. Calhoun : The Montana lobe of the Keewatin ice-sheet. Professional Paper 

 No. 50. U. S. Geol. Survey. 1906. pp. 8 and 9. 

 s Bull. Geol. Soc. Am., vol. 13, p. 310. 



