CHANNELED SCABLANDS OF THE COLUMBIA PLATEAU 647 



this has been named the Spokane glaciation.^ It assuredly is not an 

 early phase of the Wisconsin glaciation. That is recorded by pro- 

 nounced moraines on the plateau west of Grand Coulee, in Columbia 

 Valley north of the mouth of Spokane River, and in Colville Valley 

 north of Spokane River. The Spokane ice left no terminal moraine 

 and very little ground moraine. The reverse relation exists regard- 

 ing the glacial waters of the two glaciations, for the Spokane glacial 

 waters were of prodigious quantity and the Wisconsin waters of little 

 consequence. Furthermore, a long time elapsed between the two 

 glaciations as shown by the relative volume of talus accumulations 

 in tracts swept by glacial streams of the two epochs. Post-Spokane 

 talus in almost all places stands three-fourths to four-fifths of the 

 total height of the basalt cliffs, post-Wisconsin talus stands about 

 halfway up on the cliffs of Grand Coulee.^ 



For the absence of a terminal moraine along the southern 

 edge of the area reached by the Spokane ice sheet, the writer has as 

 yet no satisfactory explanation. It seems clear, however, that a 

 morairie never was deposited, rather than that it was once built 

 and subsequently removed. The functioning of some scabland 

 tracts absolutely required glacial ice against the north slopes of the 

 unglaciated hills at their heads. Floated granite erratics among 

 some of these hills also require blocking of valleys by glacial ice. 

 Yet there is no evidence of lateral drainage along the ice front in 

 contact with the unglaciated hills, to which might be ascribed the 

 removal of a terminal moraine. 



The Spokane glaciation cannot be dated very far back in the 

 Pleistocene, else the scablands should have a soil mantle of eolian 

 sand and dust and disintegrated basalt, and the hundreds of lakes 

 in the old channels should have been destroyed. 



Leverett has suggested that a pre-Spokane till beneath loess at 

 Cheney is of Kansan age.^ If it is, and if the post-Spokane glacia- 

 tion is correctly ascribed to the Wisconsin epoch, the Spokane 



' J H. Bretz, "Glacial Drainage on the Columbia Plateau," Bulletin of the Geological 

 Society of America, Vol. XXXIV (1923), pp. 573-608. 



^ This question of differentiating Pleistocene epochs by talus accumulation will be 

 discussed more fully in a separate paper. 



3 Frank Leverett, Bulletin of the Geological Society of America, Vol. XXVIII (1917), 

 P- 143- 



