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 



