48 



//. F. Held — Studies of Muir (Jlacier. 



been overturned so that it could not have arisen vertically out of 

 the water. 



Let us picture to ourselves what takes place at the end of the 

 glacier, noting first that there are three ways in which the ice 

 breaks away : (a) a piece may break off and fall over — this is the 

 usual way with small pinnacles ; (b) a piece may shear off and 

 sink into the water — this is the usual way with the larger masses ; 

 or, again, (c) ice may become detached under water and rise to 

 the surface. The diagrams in figure 2 illustrate what I conceive 

 to be successive forms of the ice-front. They show how, after a 

 number of pieces break off from above, one large piece will break 

 off" from below, but, in all probability, not from near the l)ottom. 

 The broken line shows where the break occurs. The dotted lines 

 show the form of the front just after the last break. 



FniURE 2 — End of a Tide-ivater Glacier. 



In addition to waste by breakage, thfere is the -waste by nj cit- 

 ing. Above the water surface this is unimportant, for there 

 the cjuantity of ice floated aAvay is much greater than that 

 melted; but near the bottom of the glacier, where the motion is 

 very slow, the melting is the principal, probably the only, cause 

 of waste, for the ice is in contact with water which is probably 

 not very cold* and is, moreover, salt. That the ice does melt 



* Professor Wright found the surface water in Muir inlet to be 40° F. 

 I did not take the temperature, but I was once much astonished on 

 putting my hand into the water to find it not at all cold, although there 

 was a large amount of ice floating about. This high temperature must be 

 due to the tides and warm winds ])revailing here, and to the compara- 

 tively warm sea near by. 



