GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 35 



part of the glacier, in early July, showed that a differential movement between 

 adjacent strata seemed to be taking place (plate x, figure 4) , the upper layers being 

 pushed beyond the lower. There was not enough foreign matter in the layers to 

 explain the phenomenon by differential melting. In the case of the South Point 

 and other Greenland glaciers Prof. T. C. Chamberlin observed a jutting of the 

 upper stratum which was apparently due to the more rapid melting of the under 

 layer, owing to its heavier load of dark-colored debris and consequent more rapid 

 absorption of the sun's heat. Upon the same glacier, however, he found verj- 

 conclusive evidence that the upper stratum may be pushed bodily over the lower, 

 giving rise to a shearing action between the adjacent strata.' In August, 1903, 

 Prof. I. C. Russell found a similar phenomenon on one of the small glaciers 

 visited on the Three Sisters, Oregon. In this case he thought the evidence con- 

 clusive that the jutting of the upper stratum was due to differential melting.^ 

 In order to ascertain vvhether or not this was a similar case of shearing, a place 

 was selected 50 to 52 feet above the base of the ice and heavy spikes driven into 

 the ice until their heads were flush with the surface. Three were placed in the 

 base of the upper stratum, about three feet thick, and three corresponding ones 

 in the upper part of the subjacent layer, which had a thickness of about two feet. 

 July 21 the upper layer projected beyond the lower 19.7 inches at the place selected 

 for observation. Two days later it was evident that the melting was greater 

 upon the upper layer, in spite of which it now projected 24.4 inches beyond the 

 lower. The spikes were now visited regularly for 10 days, July 25 to August 3, 

 the amount of melting measured, as well as the amount of projection of the two 

 layers, and the spikes reset. These measurements were necessaril}" rough, but 

 they showed each day that the melting was greater upon the upper stratum, 

 the average amount for each spike being 1.76 inches, while that for the lower 

 stratum was 1.53 inches, or nearly I inch less. Some sand and fine gravel, 

 washed down from above, daily accumulated in the lee of the projecting upper 

 layer and gave the appearance of a concentration of dirt in the upper part of the 

 lower stratum. When this dirt was small in amount it was observed that melting 

 was accelerated; when greater in amount, that the melting was retarded. The 

 upper stratum continued to gain slowly, but irregularly; reached a maximum 

 of 26.6 inches and closed at 25.6 inches, or about 6 inches more than at the begin- 

 ning of the observations. The results are tabulated below for inspection. Time 

 did not permit the verification of the results at other points where the same 

 thing appeared to be taking place, but there seemed to be no question tha t the 

 upper layer was moving bodily over the lower. This movement represents a 

 shearing of the body of the glacier, the shearing-plane lying between the adjacent 

 strata, but not a shearing of the ice itself. Knowing how readily iron absorbs 

 heat it may be supposed that six-inch spikes might induce melting sufficiently 

 to render their use unsatisfactory. Lying in the ice horizontally there was con- 

 siderable melting about the outer half of the spike, allowing it to sag and slide 



'Journal of Geology, vol. iii, 1895, p. 676. 



' " Glacier Cornices," Journal of Geology, vol. xi, 1903, p. 783. 



