PLEISTOCENE SUBMERGENCE IN COLUMBIA VALLEY 501 



overlie the lake beds, the gravels having been carried down Grand 

 Coulee from the Okanogan Lobe during the subsiding stages of the 

 submergence. 



The situation of these deposits near the ice and at the northern 

 extremity of the submergence, and the presence of intercalated 

 gravelly strata make a strong case for their origin in Lake Lewis. 

 If the interbedded gravels were known to contain material of 

 glacial derivation, the case would be clear. Schwennesen and 

 Meinzer think that this lake was local, and that it discharged to the 

 present valley of the Columbia over two abandoned cataracts south 

 and a little west of Quincy. They apparently do not accept the 

 hypothesis of a Lake Lewis as enlarged and set forth by Russell. 



Gravel terraces in the Columbia Valley. — Russell and others have 

 noted the presence of several terraces of gravel at different levels 

 in the Columbia Valley from Chelan upstream. The Great 

 Terrace, as Russell called it, appears to be the highest gravel bench 

 in this part of the Columbia Valley. Its altitude near the down- 

 stream termination is 600 to 700 feet above the Columbia according 

 to Russell. The Columbia at the mouth of Chelan River is 670 

 feet A.T., and the surface of the terrace therefore is 1,270 to 1,370 

 feet A.T. If the Great Terrace is a delta built in Lake Lewis, as 

 Russell thought, and if the present termination is the original delta 

 front, the submergence stood between 1,270 and 1,370 feet in this 

 part of Washington. 



The high line of drifted debris is not known to reach above 

 1,283 feet A.T., though of course the highest bowlders may not 

 have been found. At any rate the close approximation in altitudes 

 strengthens Russell's case for the delta origin in Lake. Lewis of the 

 Great Terrace. If top-set beds on fore-set beds are ever found in 

 this terrace their presence will settle the matter affirmatively, and 

 the altitude of their contact will give the precise upper limit of the 

 submergence in this part of the state. If Russell were correct about 

 this, there should also be deltas correlative with the Great Terrace 

 in such tributary valleys as carried glacially fed, and therefore 

 actively aggrading, streams at this time. 



The Columbia Valley contains gravel terraces at intervals from 

 the Great Terrace to Portland. Too little is known of these to 

 attempt their interpretation here, but thfe upper limit of each 



