1906.] NATURAL SCIENCES OF PHILADELPHIA. 577 



fact that the glacier at one time covered the entire bottom of the 

 valley, and that the medial moraines which are now noted between the 

 several sections of the glacier were at that time carried entirely on its 

 back down the valley and deposited far below, without leaving any trace 

 of the route which had been originally taken. 



It has been known for a number of years that some portions of the 

 Wenkchemna Glacier were advancing, or rather that from time to time 

 masses of moraine which had rested almost upon the limit of the ice 

 had been shot down upon and partly or completely covered living trees 

 of the forest, which in places comes directly up to the ice wall. A 

 comparison of photographs taken in previous years with the condi- 

 tions as they were found in July, 1906, indicated that at the points in 

 question no material advance of the ice could have taken place, and yet 

 at these very points there was evidence of masses of moraine being 

 projected on the ground below. The fresh rock was thrown beyond the 

 limit of the ice, which to all observation had not changed recently. 

 The base of the glacier close to the ground gave evidence of not having 

 changed for a number of years, but from the ice slope above masses of 

 rock were and had been precipitated over and beyond the older rocks 

 and upon the grass and trees. 



A careful consideration of these unusual conditions seemed to offer 

 but one satisfactory solution. The ice forming this glacier, or rather 

 composite glacier, is largely contained in a hollow or basin, from the 

 bottom of which drainage is provided to the lake below. The ice 

 extends above the edges of the basin, in many places covered deeply 

 with moraine. The pressure upon the ice from behind causes a slow 

 but steady motion of the upper strata towards the edges, which sets up a 

 shearing action of one layer of ice on that below. The result is that the 

 upper part of the moraine, very thin and unable to withstand the pres- 

 sure, is pushed outward by the ice till it falls over the edge of the lower 

 and more stable portions and upon the green grass or forest beyond the 

 limits of the basin. It is evident that this action is much more active 

 at certain points than at others, and an attempt was made to determine 

 whether the position of the edge had anything to do with it, without 

 satisfactory results. 



Wliatever may finally be determined as to the cause of change in tne 

 ice edge, a tramp over the glacier surface gave many evidences of great 

 and continued shrinkage. The moraines everywhere showed that 

 though they had been recently formed the ice was then many feet 

 thicker, and a series of very beautiful rock cones, which rested on the 

 solid ground but were surrounded by ice, bore silent witness to the 



