118 THE GLACIAL LAKE AGASSIZ. 



a height of 4,400 feet above the present sea-level. The Hand Hills are stated by Mr. 

 Tyrrell to be unglaciated above a height of 3,400 feet,' and as these hills are situated 

 N, 40° W. from the western end of the Cypress Hills, ^t a distance of about 150 

 miles, a line connecting the bases of the driftless parts of the two plateaus would 

 incline toward the northwest at a rale of (5.7 feet per mile, and would have an average 

 elevation above the present surface of about 1,550 feet. Drift was also observed by 

 Dr. G. M. Dawson on the West Butte [of the Sweet Grass Hills] at an elevation of 

 4,660 feet, or 1,260 feet above the level at which it disappears in the Hand Hills, 

 which are in nearly the same meridian, and 260 feet above the same point in the 

 Cypress Hills. These differences in level, divided by the difference in latitude of 

 the several elevations, afford evidence of a Post- Tertiary dejiressiou of the plains to 

 the north in this region, relatively to those in the vicinity of the forty-ninth parallel, 

 of about 7.2 feet per mile. The glacial sea or continental glacier is also shown, by 

 subtracting the elevations given above from the present level of the surface, to have 

 had a maximum depth in the plains surrounding the Cypress Hills of 2,000 feet, and 

 to have averaged about 1,500 feet.^ 



On the Rocky Spring' plateau, 25 miles west-southwest from the West 

 Butte, the upper limit of the drift is reported by Dr. Dawson to have an 

 elevation of about 4,100 feet. The descending slope of the ice-sheet thus 

 indicated for this distance is 22 feet per mile. 



In New England, as before noted, we are indebted to Prof. C. H. 

 Hitchcock for the proof that the ice-sheet enveloped the top of Mount 

 Washington, which has a height of 6,293 feet; and in Bi-itish Columbia 

 Dr. George M. Dawson finds that it covered mountains 5,000 to 7,640 feet 

 high, and he estimates that its highest central part upon that province "had 

 an elevation of at least 7,000 feet above the mean elevation of the interior 

 plateau, which would be equivalent to an elevation of about 10,000 feet 

 above the present sea-level, or probably 11,000 feet above the sea-level 

 of the time."' Between these eastern and western areas of great known 

 thickness of the ice, as determined by the height of glacial drift and striae 

 on mountains, probably the ice-sheet across the interior of Canada at one 

 time attained a thickness of a mile or more on a central belt several 



'Mr. Tyrrell, in the later Annual Report of the Ciinadian Geol. Survey, Vol. II, for 1886, 

 p. 145 E, gives this aa "about 3,200 feet." [W. II.] 



-Geol. and Xat. Hist. Survey of Canada, Annual Report, new series, Vol. I, for 1885, pp. 75 aud 

 76 C. Also see Dr. George M. Dawson's descriptions of the superficial deposits and glaciation of the 

 Bow and Belly rivers, ibid., Report of Progress for 1882-83-84, pp. 139-152 C. 



3 Trans., Roy. Soc, Canada, Vol. VIII, sec. 4, p. 28. 



