ALASKA GLACIERS 
138 
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 realty 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 
