GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



tween the rate of movement of center and sides must open marginal crevasses. 

 In the rock scorings seen near the nose of the Illecillewaet, the frontal and lateral 

 grooves about the knobs and trails suggest very strongly a plastic condition 

 of the ice. In the case of the same glacier, but farther up between the ice and 

 the left lateral moraine, the ice was seen moving over a knob of bedrock not 

 fully exposed in 1904. Transverse crevasses formed above while the ice melted 

 below and there were formed strips of ice, 20 to 25 feet long, supported at either 

 end. Moving downward these strips were suspended in the air, and in 

 the course of ten days in September one bar had sagged so as to be very no- 

 ticeable to the eye, without forming any crevasse large enough to be noticed, or 

 to permit of the destruction of the ice bar itself. This phenomenon seemed to 

 indicate that the ice could, to some extent, yield to a tensional stress. 



Now that the question of the plasticity of granular ice has been settled by 

 experiment, what objections are there that may be urged against its application 

 to the glaciers ? Crevasses and faultings indicate simply that there is a limit to 

 its plasticity, as indeed there is to the most typically plastic solid. The tendency 

 to flow must be greater in the basal layers, but it does not necessarily follow that 

 with the friction of the bed to combat, the velocity here will be greater than or even 

 equal to that of the upper layers. The hold which glaciers have upon rocks in 

 their basal layers is probably not a firm one. It seems to the writer that the 

 chatter-marks, crescentic gouges, the shape and often sudden termination of 

 the coarse striae, as well as the faceted condition of the boulders in the ground 

 moraine, all indicate that the glacier was persistent, rather than firm, and that 

 it very often lost its grip. All of the phenomena of rock scoring, the subglacial 

 fluting of the ice, the compression of the ice at the base of a slope, the phenomenon 

 of shearing, and the mounting of reversed slopes prove that portions of the ice 

 move bodily under the influence of a more or less rigid thrust from behind. This 

 necessary amount of rigidity in the ice is not inconsistent with the degree of plas- 

 ticity ascribed to it. When the flow is not sufficiently rapid at any point the 

 ice must be thrust forward bodily. The most forcible argument against this 

 modification of the viscous theory of glacial movement is brought forward by 

 Chamberlin. It would seem that the granules should be distorted noticeably in 

 the direction of flow. That this distortion is not more apparent may be due to 

 the complete mechanism of granular growth. It may be disguised by the shear- 

 ing of the granules in the direction of the basal planes and their later dry union 

 by the principle of Hagenbach-Bischoff. 



9. COLOR OF ICE AND GLACIAL WATER. 



The exquisite richness and variety of coloring seen in glaciers and glacial 

 lakes constantly arouses the wonder and admiration of those privileged to gaze 

 upon them. The colored photograph fails to reproduce it and it eludes the 

 brush of even the most skilful artist. An explanation of the cause of this color- 

 ation can scarcely fail to be of interest. In 1904 a study was made of several 



