700 5. R. CAPPS AND E. D. K. LEFFINGWELL 



topographic form and physical constitution, with the character of 

 the surface upon which the deposits were laid down, and with the 

 material which the ice had to handle. In the Evergreen Lakes 

 glacier, for example, the drift has a characteristically new appear- 

 ance, both in respect to its materials and its topography. The mate- 

 rial of the drift of the Lake Fork glacier, on the other hand, looks 

 very old. There are few large bowlders at the surface, and most 

 of the rock material in the drift is notably decayed. But the topog- 

 raphy of even this moraine is new, and it was, without question, con- 

 temporaneous with the newer appearing drift of the Evergreen 

 Lakes moraines. 



The difference in the material in these two cases is to be explained 

 by the difference in the condition of the rocks over which the two 

 glaciers moved. Even now the bed-rock in the upper part of the 

 valley of Lake Fork is deeply decayed, showing that the glacier 

 did not clean out even all the decayed rock. The upper part of the 

 area out of which the Evergreen Lakes glacier moved is of hard 

 fresh rock, showing that the ice of the glacier removed not only all 

 decayed rock, but also some of the fresh rock beneath. The fresh- 

 ness of the drift deposited by this glacier shows that much undecayed 

 rock was worn away by the ice. 



The glaciers terminated in two classes of situations, and their 

 terminal deposits stand in a somewhat definite relation to the position 

 of the ends of the glacier. The ice in the valleys of Homestake and 

 Rock Creeks, and in the valley west of Mitchell, never reached a 

 Piedmont plain upon which they could deploy, but ended in the 

 narrow mountain valleys. Under these conditions there was no 

 opportunity for the terminal deposits to accumulate in great terminal 

 moraines, since the abundant water from the melting ice carried the 

 drift away about as fast as the ice left it. No terminal moraines of 

 consequence occur at the ends of these glaciers. 



The other larger glaciers of this region sent their ice beyond the 

 confines of the narrow valleys, and deployed to some extent on the 

 valley plain beyond, building great terminal moraines. These two 

 types of termini and of terminal accumulations are well shown by 

 the glaciers of Homestake Creek, on the one hand, and those of Lake 

 Fork, Clear Creek, and Half Moon Creek, on the other. The absence 



