54 



STEPHEN R. CAPPS 



Feet 



tion at the top of a 1,600-foot hill just east of the boundary. The 

 glacier also covered the ridge of which Ping Pong Mountain is the 

 west end. Unlike the ice-fields which occupied the Nabesna and 

 Chisana valleys, this one was not fed by tributaries from both sides 

 of its valley, but only from the valleys of the high mountains to the 

 south and west. 



The severity of the glacial erosion upon the valley walls is well 

 shown by the abrupt triangular faces of the spurs opposite the mouths 

 of North Fork and Solo creeks. 



Solo Creek gravels. — ^North and west of Solo Creek there is a broad, 



flat area covered with 

 outwash gravels, which 

 were laid down under 

 much the same condi- 

 tions as were those east 

 of the Chisana Glacier. 

 Here the receding ice 

 in the White River Val- 

 ley left bare a broad 

 area which normally 

 drained into the White 

 River. The drainage 

 was here impeded by 

 the valley glacier, which 

 must have occupied the 

 valley long after the higher area to the north was deglaciated. During 

 this period of obstructed drainage extensive gravel beds were laid 

 down, which abutted against the ice to the south, and spread north- 

 ward and filled the old drainage channels. The filling went on to 

 such an extent that some of the streams found a lower outlet to the 

 northeast, and still flow in that direction. Solo Creek has now cut a 

 considerable gorge through the gravels and into the underlying rock, 

 and is gradually recapturing for the head of the White River the drain- 

 age lost during early glacial times. 



Ptarmigan Lake gravels. — ^Between North Fork and Ping Pong 

 Mountain, a broad flat has a gravel covering due to the same causes 

 as those which brought about the deposition of the Solo Creek gravels. 



i5'G/ac/a/ till 



8'Grave/ ibeds contorted 

 bij overriding ice 



27' Coarse, rudel^i 

 stratif/ed ^rQ.ve!s 

 and sa/idg. 



Fig. 12. — Section of terrace on White River, 

 showing glacial till above, and gravels below. The 

 upper portion of the gravel beds has been distorted 

 by the over-riding ice. 



