544 PKE-WISCOXSIK GLACIAL DBIFT IX MOXTAXA 



that the glaciation of the Blackfoot peneplain occurred at a time when 

 Saint Mary Valley had not been eat down to so great a depth by some 

 hundreds of feet, and that dissection of the plain to the east had not 

 proceeded so far as the development of the second set of plains. 



It is not necessary, however, to suppose that Saint Mary Yalley was not 

 cut at all below the level of the adjacent plain, nor that the Blackfoot 

 peneplain was as yet relatively little dissected for any considerable dis- 

 tance to the north and south beyond the limits of the Browning quad- 

 rangle. 



Let a generalized profile be drawn approximately along the line of 

 axial flow through Marias Pass and out across the plain of Two Medi- 



fo:o 



3XG 



: 



Figcke 5. — Profiles from Gmnmight Pass and Bear Creek Y alley 



Number 1. — Profile from a point near Gunsight Pass fA) down Saint Mary VaUey to 

 the foot of the upper lake, <Bi and thence northeastward across Saint Mary Ridge and 

 other drift-covered remnants of the Blackfoot peneplain. 



Somber 2. — Profile from upper part of Bear Creek Valley near Fielding (A), north- 

 eastward through Marias Pass and over the hills (B) east of Lubec, and thence across 

 that part of the plain overridden by Two Medicine Glacier at the Wisconsin stage of 



cine Glacier (figure 5, number 2), and a like profile be drawn from the 

 divide near Gunsight Pass, down Saint Mary Yalley to the foot of the 

 upper lake, and thence northeastward across Saint Mary Bidge and the 

 remnants of Blackfoot peneplain (figure 5, number 1). Superposing 

 one on the other, it appears that were Saint Mary Valley about 1,000 

 feet less deep than now, the obstruction interfering with the extension 

 of ice directly northeastward from the northern catchment basin would 

 not be greater than were the obstructions in the path of Two Medicine 

 Glacier. 



Judging from the exposures seen in 1911 and 1912, the upper . 

 feet or more of the highest part of Saint Mary Bidge is pre-Wisconsin 



