5o6 / HARLEN BRETZ 



extent than, and different genesis from, those resulting from the 

 weight of an ice sheet. In this respect it differs notably from the 

 Champlain submergence of northeastern America. 



This h3^othesis of a hinge line along the Cascade axis can be 

 most satisfactorily framed in terms of lesser re-elevation west of 

 the range, after the submergence. It is strengthened by the 

 existence of the drowned and alluvium-filled stream valleys of 

 Puget Sound, ^ of the Columbia west of Portland, and of the smaller 

 Chehahs and Willapa valleys. The Columbia east of the Cascades 

 is on a rock floor in many places as far downstream as The Dalles, 

 Oregon. 



On the map of the Columbia submergence (Fig. 2) Willamette 

 Sound is assumed to have reached a maximum height of 400 feet. 

 Enough of the valley has been topographically mapped to show 

 that in such a submergence a narrow strait must have existed just 

 south of Portland, and probably another at Salem. Through these 

 straits all the Willamette Valley drainage moved northward. 



Diller reports foreign bowlders about Corvallis, south of both 

 straits. It seems impossible that bergs in the Columbia Valley — 

 could have been drifted southward through both straits against 

 the northward flow which must have existed in them. This 

 situation is very strongly suggestive of a submergence in the 

 Willamette Valley even greater than that shown in Figure 2. 



When one plots the approximate extent of this submergence in 

 the Columbia Valley on a map, he finds that there were two 

 broadened portions, one on each side of the Cascade Range, con- 

 nected by a narrow strait in the gorge, and the whole joined to the 

 Pacific by another strait across the Coast Range. If we were 

 dealing with an existing water body of such outline and magnitude 

 we would almost surely find different names applied to such 

 portions. It is therefore proposed to redefine the names "Willam- 

 ette Sound" and "Lake Lewis," as outlined in this paper, and to 

 continue their use; to recognize the existence of two elongated 

 straits, one across the Cascade Range, the other across the Coast 

 Range; and to consider the whole as " The Columbia Submergence " 

 of the Champlain epoch. 



^ J H. Bretz, "Glaciation of the Puget Sound Region," Wash. Geol. Surv. Bull. 8 

 (1913), chap. viii. 



