GLACIAL DRIFT. 321 



land, we find that 800 miles represents the distance to central Labrador, 

 requiring a cap 7 miles higher than Mt. Washington, or over 8 miles thick 

 in all. If the movement came from Greenland, the distance is estimated 

 at 2,000 miles, and the elevation of the ice-cap at 17 miles above Mt. 

 Washington Prof. Dana, from somewhat different data, obtains smaller 

 results. Assuming the starting-point to have been on the height of land 

 between the St. Lawrence and Hudson's bay, and the descent at 15 feet 

 per mile, the sheet must have been at least 13,000 feet thick above the 

 land to carry it over Mt. Washington. These figures sound less formid- 

 able, but the slope does not seem adequate to have produced the results. 

 Prof. Torell, of Sweden, read a paper before the American Association 

 for the Advancement of Science, in 1876, advocating the source of the 

 American drift to have been in Greenland. He writes thus : * 



It has been the opinion of many distinguished American geologists that the source 

 of the eastern ice fields is to be sought in the Canadian highlands. Against this opin- 

 ion several important reasons may be urged. First : in the portions of Canada in 

 which the glaciers in question are supposed to have originated we have reason to be- 

 lieve that the rocks are rounded and scratched, phenomena everywhere recognized as 

 glacial, — but I think in no case characterizing rocks known to have been covered with 

 perpetual snow. Again : the elevation and extent of the highest portions of Canada 

 are hardly sufficient to account for the requisite accumulation of snow and ice. And 

 finally, so far as I have learned, there is not found upon the rocks of the northern 

 slope of Canada, nor yet in boulders moved by glacial force, any satisfactory evidence 

 that there had been a northward as well as southward movement of glaciers from the 

 highlands of Canada. If, therefore, the phenomena of the northern and eastern 

 United States, usually supposed to be glacial, are indeed such, and if there is not suffi- 

 cient reason for assuming the Canadian highlands to have been the source of the 

 glaciers which produced these phenomena, then the source of them must be sought for 

 elsewhere. 



I think it will be conceded by all geologists who have studied the glacial phenom- 

 ena of these regions, that both the character of the erratics and the direction of the 

 scratches upon the rocks show that this source must lie to the north-east. Following 

 the line of the glacial movement across Baffin's bay and Davis straits to Greenland, 

 we find the largest body of land in the northern hemisphere covered by ice and snow 

 to a depth of not less than 2000 feet, and at this moment sending down its icebergs as 

 far as the middle Atlantic. From the sixtieth degree of latitude to above the eightieth, 

 this vast area of land is known to be ice-covered, and from the scarcity of the icebergs 

 upon the eastern compared with the western coast of that land, it may be concluded 



* American yournal of Science, iii, vol. xiii, p. 78. 



