12 



GUIDEBOOK OF THE WESTERN UNITED STATES. 



Pacific line by way of Woodinville, a trip of 54 miles, or by ferry across 

 Lake Washington to Kirkland and thence by automobile, a route 

 that, for small parties, is generally preferable. At the falls Snoqualmie 

 River plunges over a great mass of lava underlain by fossiliferous 

 sediments 



of the Eocene coal-bearmg formation. 



In the immediate vicinity of Squak Mountain and Sammamish 

 Lake there are a number of large channels cut and then abandoned 

 by streams from the former glaciers. They may be reached by either 



the sound, spread over the elevated plains 

 between the valleys, and extended from 

 the foot of the Olympic Mountains on the 

 west to the base of the Cascade Range on 

 the east. On the south it reached to and 

 covered much of the plains south of 

 Olympia. The ice of this glacier was 

 pjobably coalescent on the east with that 

 descending the slopes and valleys of the 

 Cascades, to which the name Osceola 

 glacier has been applied by geologists. 



Tliese glaciers, on melting, left deposits 

 of clay, sand, gravel, and bowlders (the 

 Yashon and Osceola drift) on the elevated 

 tracts between and around the troughs of 

 the sound, but the deep depressions wore 

 unfilled, so that after the ice melted they 

 were occupied by marine waters. 



This later drift lies upon stratified sands 

 and gravels (called the Douty gravel, Pu- 

 jrallup sand, and Orting gravel) deposited 

 by waters from the melting of earlier 

 glaciers. Buried in these deposits are 

 beds of lignite, formed from vegetation 

 that grew upon the sands and gravels. 



One view as to the origin of the deep 

 troughs composing Puget Sound may be 

 stated briefly as follows: The Admiralty 

 ice sheet occupied and overflowed deep 

 valleys which had been cut when the land 

 stood higher. ^Hxen this ice melted the 

 hilly tracts between the valleys were un- 

 covered first, and the washing in of sand 

 and gravel leveled these up into what are 

 now the elevated intervalley plair.s . The 

 final melting of the tongues of ice left the 

 troughs to be occupied by mariTio water. 

 Later came the ice of the Yashon glacier, 

 and this, on melting, again left the main 

 depressions unfilled. 



According to another view the disap- 

 pearance of the Admiralty glacier left the 

 clay, sand, and gravel spread in a con- 

 tinuous sheet over the Puget Sound basin, 

 burying, in large part, the older valleys 

 and ridges. Afterward the land rose 

 about 1,000 feet and streams cut deep val- 

 leys in these soft deposits. Then the 

 basin waa depressed about to its present 

 level and the ice of the Yashon and Os- 



Tliese older sands and gravels are in places ceola glaciers filled the valleys and over- 

 much weathered and eroded; they were topped the intervening tracts, and, on 

 evidently exposed during a long inter- melting, left the area thinly mantled with 



glacial stage before they were overridden j drift and the depressions unfilled, 

 and covered by the deposits of the Yashon 



and Osceola glaciers. 



Beneath all these deposits lies a laj'cr 

 of stiff blue clay, mostly stratified but in 

 places showing no bedding and crowded 

 with Bubangular stones and large bowlders. 

 This deposit (known to geologists as the 

 Admiralty till) is supposed to have been 

 formed at a still earlier stage of glaciation, 

 when the Puget Sound basin was occupied 

 by a lobe of the Cordilleran ice sheet, as it 

 waa later by another lube at the Yashon 

 subsfa^e. Some phenomena suggest that 

 glaciers occupied the basin still earlier. 



As the main outlet of the Puget Sound 

 basin is to the north, ice-dammed fresh- 

 water lakes were for a time held in the 

 troughs at each stage of advance of the 

 ice front. ^\lien the outlet was at last 

 opened the troughs were filled with 

 marine water, which finally reached the 

 level at which we now find it. 



Marine shells found at various levels up 

 to 290 feet above tidewater show that 

 since the disappearance of the glacier of 

 the Yashou substage the ba^^in has been 

 further depressed and submerged and 

 then reelevated. 



