138 ALASKA GLACIERS 



are in part low, but include also hills and bluffs. While 

 this estuary is much larger than those of Chehalis and 

 Willapa rivers, it is small in relation to the Columbia 

 River, which carries a great volume of water, and the val- 

 ley whose submergence it records was of very moderate 

 dimensions. This valley was of course formed while the 

 river ran at a lower level, but the erosive work accom- 

 plished at that level was surprisingly small. As the con- 

 tinental shelf is narrow along this part of the coast, the 

 river may be supposed to have promptly graded its chan- 

 nel to harmony with the depressed base-level, and the 

 conditions would seem to have been favorable for the 

 development of a broad and branching valley like that 

 submerged in Chesapeake Bay. The fact that no such 

 development took place seems to indicate either that the 

 lowering of base-level was small or that the period of low 

 base-level was short. Despite the great volume of the 

 river, the valley developed by the discharge at lower level 

 was quite insignificant in comparison with the fiords and 

 channels of the neighboring glaciated coast. 



These features would have an important bearing on 

 the question of low base-level in the district of the inside 

 passages if we could be sure that the history of the 

 Columbia estuary was really pre-Pleistocene; but there is 

 reason to suspect that the Columbia has somewhat re- 

 cently come into possession of the lower part of its valley. 

 After passing the Cascade Mountains it turns northward 

 in the great structural valley which farther south contains 

 Willamette River and farther north holds Puget Sound. 

 Then at the mouth of the Cowlitz it again turns westward, 

 and traverses a low range of mountains or hills in a some- 

 what narrow passage. Close to the river these mountains 

 have a height of 1,000 feet or more. From the mouth of 

 the Cowlitz northward to Puget Sound the country is 

 comparatively low, and the summits are occupied by 



