﻿SHERZER] GLACIAL STUDIES IN CANADIAN ROCKIES 495 



rock slide for an explanation. Proceeding thus b) a process oi 

 elimination the conclusion seems forced upon us thai there is here 

 evidence of a double seismic disturbance of the entire regi< >n. ( '< >arse 

 fragments, more or U^s weathered to start with, were shaken loose 

 from the overtowering cliffs and peaks and dropping into the neve, 

 or upon the ice, were not ground into fragments as they ordinarily 

 are when they descend into the valley. The protection afforded the 

 ice by this material brought about a halt in the frontal retreat then 

 in progress and the blocks were concentrated into two moraines 

 more or less separated. As soon as the bulk of the material, result- 

 ing from each disturbance, had been deposited the glacier then n 

 sumed its slow retreat. 



If this is the correct explanation then it may be predicted that 

 glaciers favorably situated for receiving such loads, as the Dawson, 

 Geikie and many others, will show similar block moraines, providing 

 they have not been overridden, or destroyed by later advances of the 

 ice, as is partially true in the case of the Wenkchemna. Remnants 

 of ice streams, which at the time of the disturbances were tributary 

 to other main trunks, would in no case have independent moraines 

 of such a tvpe. Neglecting the differences in the time of transporta- 

 tion, due to the varying velocities of the several glaciers as well as 

 the different distances that the material must lie transported, these 

 moraines in the various valleys may be correlated in time. If the 

 approximate age of any one set can be determined we shall have the 

 data for estimating the average rate of recession of all those glaciers 

 having such moraines, as well as ascertaining the approximate date 

 of the seismic disturbances. The oldest trees found growing upon 

 the vounger of the two moraines in the Illecillewaet and Lake Louise 

 valleys are 447 and 400 years of age respectively. In the Asulkan 

 valley a rough estimate would be obtained by adding to 250 years, 

 the time required for the glacier to retreat about i^ miles at the 

 average rate of 30 ft. a year. This would give about 500 years, the 

 excess over the preceding estimates probably being required for the 

 formation of sufficient soil to allow the trees to start their growth 

 upon such coarse moraines. The younger of the two block moraines 

 may lie regarded as between 500 and 600 years old and, allowing 

 for the transportation of the material, the earthquake, if such really 

 occurred, probably happened during the thirteenth century. The 

 outer moraine is probably 150 to 200 years older than this inner. 



Through the kindness of Mr. Frank B. Taylor the writer's attention was 

 called to a rather remarkable earthquake which seems ti> have severely 

 affected Canada and the adjoining portions of the United States in 1663. 



