720 - ROLLIN D. SALISBURY 



and berg deposits, having their source in the northeastern ice, 

 overHe the till laid down at an earlier time by the mountain 

 glaciers. 



4. The valley glaciers belonged to a recent epoch. They 

 were certainly not earlier than the Iowa epoch, and probably as 

 recent as the Wisconsin. 



5. The drift of the northeastern ice sheet is of Wisconsin, 

 possibly late Wisconsin age. 



6. So far as the evidence gathered shows, the length of time 

 which elapsed after the deposition of the Rocky Mountain drift, 

 and before the deposition of the drift of the ice sheet from the 

 northeast, was not great. 



7. The time since the last glacial epoch, as shown by several 

 lines of evidence in the area studied, seems to have been geo- 

 logically short. 



8. The Sweet Grass Hills, situated just south of the 49th par- 

 allel and about thirty miles back from the edge of the ice sheet 

 from the northeast, were not covered by the ice. The hills stood 

 as three great nunataks, the highest reaching about 2000 feet 

 above the surface of the ice. 



9. The slope of the surface of the continental ice sheet 

 between its edge and a point 25 miles back from its edge was 

 estimated at about 50 feet per mile. This determination was 

 made in the vicinity of the Sweet Grass Hills. The slope of the 

 surface of the ice in various valleys was also determined. 



10. The existence of a long narrow lake in front of the edge 

 of the Continental ice sheet, and between it and the mountains, 

 was proved, and its extent determined. 



11. Considerable changes in drainage were effected by the 

 ice. Some data were gathered which throw light on the former 

 courses of the Missouri, the Teton, and the Two Medicine rivers, 

 and of Buck, Muddy, and Cut Bank creeks. 



Besides these conclusions touching glacial problems, some 

 other observations were made : 



12. The region studied shows at least three periods of ero- 

 sion, when the land stood at different levels. 



