TERMINAL MORAINE OF PUGET SOUND GLACIER 169 



feet, falling short a few tens of feet of reaching the summit. No 

 till has been found in the valleys of any of the south-flowing streams 

 of the region. 



Summit Lake lies in the upper part of a preglacial valley, the 

 lower southern portion of which bears a drift rilling. The ice 

 sheet certainly overrode the divide at the northeast of Summit 

 Lake but it brought over no drift. Farther south, however, the 

 valley opens into a larger one trending east and west, and from 

 both directions in this, till was carried into the Black Hills. Again 

 the relation of agriculture to the drift is illustrated in the occurrence 

 of several small farms on the broadened valley floor produced by 

 drift filling while elsewhere the region is covered with primeval 

 forest or the waste of logged-off land. 



At least two distinct valley trains cross the western part of the 

 Black Hills to the Chehalis River, the larger of these being a filling 

 so complete that several rock hills rise like nunataks from the 

 gravel plain. This enters the Chehalis valley at Elma, in the 

 vicinity of which it is deeply incised by creeks, its structure being 

 thus plainly revealed. A feature of the gravel is the prevailing 

 reddish color, fairly uniform throughout the mass. The freshness 

 of the pebbles and the youthfulness of drainage on the plain, 

 however, show this staining to be due to some other cause than 

 age. The Vashon till near the head of this valley train is also 

 deeply red while its pebbles are fresh. The explanation is thought 

 to be found in the incorporation of residual material from the 

 basalt rocks of the Black Hills. 



The country lying between these hills and the Olympic Moun- 

 tains is practically a great gravelly waste. The forest is thin over 

 large areas and open prairies occur in the region south of Hood's 

 Canal. The moraine hills when found are often largely buried in 

 outwash and the extreme limit of the ice as mapped is consequently 

 only approximate, being based on the occurrence of till outcrops 

 above the gravel plain. No definite ridging tangential to the ice 

 margin was observed in the till hills seen, though their occurrence 

 forms a zone a few miles wide, whose outer margin has been indi- 

 cated as the limit of Puget Sound ice to the west. 



The character of the till, where exposed in railroad cuts and 



