GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 47 



the valley. This being the region of accumulation, rather than melting, the 

 rock debris is almost completely enveloped in snow and remains temporarily 

 covered (plate v, figure 2). As the neve" is pushed beyond the snow-line upon 

 the glacier, surface melting begins and the rock fragments begin to make their 

 appearance at the surface. As this action continues the rock rubbish is con- 

 centrated more and more, forming an almost complete veneering over the lower 

 third of the glacier, completely obscuring the ice except where it has been incised 

 by the drainage streams. The most of this material is sharp and angular, con- 

 sisting of irregular fragments .of quartzite, sandstone, limestone, dolomite, and 

 quartz and argillaceous schists; in the main of Cambrian age. The ice lying im- 

 mediately to the west of the medial moraine has come from the Lefroy side of the 

 valley and being less well covered with de"bris has experienced more surface 

 melting. This depression thus formed, shown in the cross-section along the line of 

 plates (page 30), determined the position of the main drainage stream, previously 

 described. The effect of this debris, in general, is to retard surface ablation 

 and recession about the nose, so that the glacier attains a lower altitude than 

 would otherwise be possible for it under the present climatic conditions. So 

 far as we may judge from the ice front, the walls of the tunnels, crevasses, mou- 

 lins, and drainage streams, the Victoria is not carrying much englacial material. 

 A portion of this is in the position originally deposited in the neVe" and a portion 

 has worked down from the surface by means of the crevasses, as shown in plate 

 xm, figure 4. 



b. Lateral moraines. Along the margins of the upper Victoria and Lefroy 

 conditions are especially favorable for the reception of rock detritus, both from 

 the action of the ice avalanches and from the various weathering agencies that 

 are operating upon the overtowering cliffs. Material derived from the cliff walls 

 will ordinarily be sharp and angular, but may rarely show a single glaciated 

 face, produced when in its original position during an earlier stage of glaciation. 

 Most of this has been pried loose by the water in the seams and joints expanding 

 in the process of freezing. The material carried by the hanging glaciers is almost, 

 if not entirely, subglacial and has been subjected to severe abrading action 

 between the ice and its rocky bed. Boulders, cobbles, and pebbles have had their 

 corners and edges partially rounded, have had their faces bruised, gouged,. and 

 irregularly scratched, and are embedded in glacial sand and clay, of a bluish gray 

 color. This ground-morainic material, mixed indiscriminately with that from 

 the cliffs, is heaped up along the neVe" margins, embedded in snow and ice. 

 Moved slowly along, very slowly compared with the central portions of the ne"ve", 

 the quantity is augmented and by the time the snow-line is reached there is 

 formed a thick band of this debris covering the margin of the ice. Protected 

 from the action of sun and rain more effectually than the general surface 

 of the glacier, in spite of its debris covering, the ice beneath melts less rapidly 

 and the marginal material is gradually elevated, with reference to the general 

 surface. About the sides of this marginal ice ridge the debris slides and rolls 

 down, allowing the less well protected ice above to melt into a sharp crested 



