GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 23 



out beyond the base of the cliff. Upon the western or Lefroy side of the upper 

 half of the Mitre Glacier, there is thus heaped up a mass of pulverized ice, which 

 is compacted by freezing into strata. This mass constitutes a new glacier, 

 since the structure of the original one must have been destroyed by the plunge, 

 with the exception of the granules and their fragments. Such a glacier is said 

 to be "reconstructed," or "regenerated." Furthermore, this new glacier 

 rests upon the back of the Mitre; is nourished differently; is of a different form; 

 has its own distinct set of strata, unconformable with those of the Mitre; moves 

 across the valley instead of lengthwise of it, and is accomplishing a totally 

 different geological work. This glacier, for which the term Lefroy is appro- 

 priate, is one of the best known examples of what Forbes termed a "parasitic 

 glacier," 1 far better, indeed, than the type itself. It is parasitic in the sense 

 that it is carried by its host, the Mitre, and in that it is nourished entirely by 

 snow and ice which would be otherwise available for the host. 



Just what is the structural relation of the Lefroy to the Mitre, the parasite 

 to its host, can only be conjectured, since the contact was not observed and the 

 plane of separation may not be at all distinct. There is, however, a very 

 evident, deep-seated motion down the valley and an equally evident 

 superficial motion across from the base of Lefroy to the foot of Aber- 

 deen. The result of the latter motion is to carry most of the ground-morainic 

 material, such as clay, sand, bruised and scratched pebbles and boulders, which 

 has been manufactured beneath the hanging glacier of Lefroy, entirely across 

 the valley and dump it in a great heap upon the eastern or Aberdeen side 

 of the Mitre (plate vin, figure i, and plate xv, figure i). The front of the 

 parasitic Lefroy being parallel with the side of the Mitre, some of the ground- 

 morainic deposit is arranged in ridges parallel with the side of the latter, in 

 which form it is being dealt out to the Victoria. Until the above stated relations 

 were discovered it was a serious puzzle to ascertain how a glacier could get its 

 ground moraine upon its own back and arrange it in ridges parallel with its side 

 (see plate xv, figure i ) . That the material could not have come from Mt. Aberdeen 

 was evident from the fact that it does not support a hanging glacier upon its 

 western face, as shown in plate vui, figure 2, although there is a buried mass of 

 stagnant ice upon the northern shoulder. Avalanches of snow and the ordinary 

 processes of weathering have brought down considerable angular material from 

 Aberdeen which covers most of the ground-morainic deposit from the opposite 

 side of the valley. While this ground-morainic material is being moved east- 

 northeast by the Lefroy for a distance of i ,800 to i ,900 feet, it is also being carried 

 north -north west for a distance of about 3,800 feet by the underlying Mitre and 

 the resultant motion is somewhat east of north. This will be made clear from 

 an inspection of the map, plate in. 



Opposite the large debris cone seen in plate iv, figure 2, upon the western 

 side of the Lefroy Glacier, there is a marked depression in the surface of the 

 ice and also across the entire tributary where it joins the Victoria, giving good 



1 Travels through the Alfs of Savoy, James D. Forbes, Edinburgh, 1845, p. 201. 



