344 J. S. Newberry — Surface Geology of the country 



tains. It flowed out to sea by the Strait of Fuca, but this 

 channel was far too narrow for it and it spread x>ver all the 

 southern portion of Vancouver's Island, planing off, rounding 

 over or deeply scoring the rocks in its passage. As the glaciers 

 retreated they left behind a sheet- of drift several hundred feet 

 in thickness, partly water-worn and stratified, partly unstratified 

 bowlder clay with striated pebbles, of which the surface was 

 nearl} 7 level. In process of time the draining streams had cut 

 in this plaifi a series of valleys all tributary to one which led 

 out through the Strait of Fuca to the ocean. After perhaps 

 some thousands of years, during which the excavation of these 

 valleys progressed, a subsidence of the land or rise of the ocean 

 caused the water to flow in and occupy the main valley and all 

 its tributaries up to the base of the mountain slopes. 



Such in few words is the history of the formation of this 

 remarkable system of inlets. They are simply the flooded val- 

 leys of a great river and of the branches that formerly joined 

 it but now empty into the extremities of the finger-like inlets 

 that have partially replaced them. 



There are but few localities in Puget's Sound basin where 

 'the rocky substratum rises so as to be visible above the water 

 level. Along the northern and western 'margin on Vancou- 

 ver's, Sucia, Orcas and Whidby Islands, and at Chuckernut's 

 and Sohome the rock appears, but at Tacoma, Steilacoom, Seattle, 

 Port Madison, Port Townsend, and it may be said generally 

 about the Sound, the shores are steep bluffs, 100 to 150 feet in 

 height composed of drift alone. From the cliffs at Port Town- 

 send and Tacoma, I took sub-angular scratched and ice- worn 

 pebbles as characteristic and convincing as any to be found in 

 the bowlder clays of the eastern States. 



The subsidence which caused the sea water to flow into the 

 subaerially excavated valleys of Puget's Sound also filled the 

 channel of the Columbia, the Cascades and the system of fiords, 

 of which these are representatives, that fringe the northwest 

 coast. We have evidence, too, that the area occupied by the 

 sea was at one time much more extensive than now, for all the 

 country immediately about 'Puget's Sound is marked with a 

 series of marine terraces which Mr. Bailey Willis, who studied 

 them carefully when connected with the Transcontinental Sur- 

 vey under Professor Pumpelly, tells me can be traced to a 

 height of 1600 feet above the present ocean level. These ter- 

 races are conspicuous on the low divide which separates the 

 valley of the Cowlitz from the basin of Puget's Sound ; and 

 here, as over much of this region, the ground is covered with 

 pebbles and water-worn bowlders, the product of the long con- 

 tinued dash of the shore waves on a slope composed of drift 

 materials. In the advance and recession of the shore line, the 



