TERMINAL MORAINE OF PUGET SOUND GLACIER 173 



Evidence of the lack of vigorous movement near the frontal 

 margin of the glacier is shown in the occurrence of deeply decayed 

 material overridden by the ice. Shale strata, profoundly decom- 

 posed, are exposed east of Little Rock. Though slightly crumpled 

 and in one case bearing an intruded arm of the till, this incoherent 

 and rotted shale has been but little eroded by the ice, though it 

 is two or three miles back from the moraine front. West of Little 

 Rock, where Vashon till is found at its farthest southern extent 

 along the Black Hills, a knob of old red till is exposed beneath it. 

 Depth of weathering and staining are the same on the slopes as 

 on the summit of this knob, hence the inference that no erosion 

 of the projecting softened till was produced by Vashon ice. 



The accompanying map indicates only the extra-morainic out- 

 wash. Great areas lie within the moraine limits of essentially the 

 same character and age. In the case of all outwash deposits, the 

 discharging water was received by the Chehalis valley largely 

 on the east or west side of the Black Hills. Extensive tracts are 

 rendered as worthless for agriculture by these outwash plains as 

 though in an arid country. For example, the road through the 

 sparse forest extending from Lake Nahwatzel to Shelton crosses but 

 one stream bed and this carries water only during the very rainy 

 winters and no valley has been cut. As already noted, the moraine 

 across the low area between the Black Hills and the Olympic foot- 

 hills has been partially buried in the flood of gravel and its relief 

 much reduced. 



The question of contribution from valley glaciers in the border- 

 ing Cascades and Olympics cannot be adequately treated in our 

 present state of knowledge. Valley glaciers in these mountains 

 on the Soundward slopes debouched into a great mass practically 

 filling the depression from rim to rim. That they would perform 

 much erosion under such conditions is not to be expected. Willis 

 has found the till sheet of a Cascade piedmont glacier on the eastern 

 part of the Tacoma quadrangle, a part of which is indicated on 

 the accompanying map. The relative insignificance of the Skoko- 

 mish glacier whose lower extremity occupied the basin of Lake 

 Cushman has been shown. No evidence has yet been found that 

 tributary glaciers north of these two produced any perceptible 



