LOW BASE-LEVEL 
137 
the streams to accomplish. The questions whether the 
broader channels of the archipelago were merely outlined 
by river gorges or were widely opened, whether the low 
peneplain was only trenched or was largely replaced by a 
peneplain at a level now submerged, whether the grading 
of river beds was restricted to the coastal district or was 
carried far into the interior, are not answered by any facts 
in my possession. 
To escape the confusion arising from the glacial re¬ 
modeling of water-wrought topography, it is natural to 
turn to the region just outside the glacial district. This 
region may be assumed to have shared the same oscilla¬ 
tions of base-level, so that whatever history may be derived 
from it can be transferred to at least the neighboring parts 
of the glacial district. The glaciation of what may be 
called the inner coast has its southern limit in Puget Sound. 
As the Olympic Mountains, separating the sound from the 
outer coast, contained Pleistocene glaciers, the outer coast 
also may have been modified by ice in that latitude. But 
farther south the coast was not directly affected by glacial 
ice. Between the Olympics and the mouth of Columbia 
River are two shallow bays, partitioned from the ocean by 
sand spits. The more northerly, Gray Harbor, receives 
the Chehalis River, a stream of moderate size, but the 
map gives no indication of a delta. Willapa Bay receives 
two small streams, Willapa and Nasal rivers, and these 
also are without deltas. It is evident that the bays are 
estuaries, or submerged portions of the river valleys, and 
they indicate a recent change in the relation of sea and 
land, the sea rising or the land sinking. 
Columbia River also ends in an estuary, its banks grad¬ 
ually separating, until near the sea they are ten miles 
apart. The estuary is shoal, and it is a matter of observa¬ 
tion that the parts protected from the current are being 
rapidly filled by the abundant silt of the river. The banks 
