COMPARISON AND EXTENSION OF TWO MEDICINE GLACIER o43 



The difference in elevation between the average height of the rim of 

 the northern basin and that of the remnants of the highest plains, in 

 which is the old drift, within 45 miles of the divide, is about 2,750 feet. 

 In the area of the Two Medicine Glacier the difference between the aver- 

 age elevation of the rim of the catchment basin and the elevation of the 

 undulating plain over which the piedmont glacier spread is about 3,400 

 feet. 



From this comparison it is seen that while the areas of the two catch- 

 ment basins are approximately the same, the difference in average eleva- 

 tions between the rims and the plains to be glaciated is about 650 feet 

 greater in the case of the Two Medicine Glacier than in the case of the 

 earlier northern glacier. From this it might be concluded that even if 

 the tributary mountain gorges and the main trough of Saint Mary Valley 

 had not then been excavated below the level of the crest of Saint Mary 

 Eidge, so that that ridge did not then stand as an obstruction diverting 

 the glacial flow from spreading freely northeastward onto the Blackfoot 

 peneplain, yet no such piedmont extension of the ice as characterized 

 Two Medicine Glacier at the Wisconsin stage would have occurred. 



The southern catchment basin has not been wholly explored by the 

 writers, but an inspection of the topography as delineated on the Marias 

 Pass topographic sheet shows that on the whole there was much more 

 obstruction to ready outflow of the ice from that basin than there would 

 have been from the northern basin were Saint Mary Valley so much 

 shallower that Saint Mary Eidge did not form a diverting dam. 



The rise from lower Two Medicine Lake to the plain on the east is 

 about 750 feet, yet the ice ascended this slope and spread eastward along 

 the south side of Two Medicine Eidge to the gap traversed by the Great 

 Northern Eailway, and then deployed freely over the undulating plain 

 about Browning. The outlet of Marias Pass east of Lubec is obstructed 

 by transverse rock ridges 500 to 700 feet in height, and farther south, 

 with the exception of Badger Creek Valley, there are no gorges opening 

 directly northeastward from the divide, and even tins valley is much 

 constricted at the mountain front. The marvel is thai a piedmont glacier 

 heading in this catchment basin should have extended so far onto the 

 plain as did Two Medicine Glacier. Considering all things, it appears 

 that if the Saint Mary Valley were not so deep a diverting trough nor 

 Saint Mary Eidge so high an obstructing dam, conditions would have 

 been about as favorable for the extension of a pre-Wisconsin piedmont 

 glacier onto the Blackfool peneplain from the northern catchment basin. 

 as they were in the ease of 'Two Medicine Glacier o\' (he Wisconsin Btage. 



From this point in the discussion it is but a step to the assumption 



