UB B. WILLIS—DRIFT PHENOMENA OF PUGET SOUND. 
ered with the heaviest virgin forest of this luxuriantly forested region. 
It is allied in form and materials to the deltas that have already been 
described, and, if such be its character, must be attributed to the initial 
epoch of retreat from the maximum advance of the Vashon glacier. The 
elevation of the water in which this delta accumulated is about 1,000 feet 
(300 meters) above the level of the plateaus a few miles to the north, 
and the ice must have had a thickness of more than 1,000 feet to have 
formed the requisite dam. 
The three high level deltas described have been mentioned in their 
sequence from the latest to the earliest. They all represent a condition 
when the northern ice-sheet ponded the waters accumulating along its 
face and held them against the hills to the south and east. The topog- 
raphy of the region was favorable to these local developments at high 
levels. No similar deltas are found toward the southwest, since in that 
direction there are no heights to confine the waters against the ice-front, 
and none have been observed further to the north, although it is quite 
probable that they exist in the favorable positions. The dense forest 
renders the discovery of isolated features a task of extreme difficulty. 
Kame terraces.*—When a glacier shrinks within its banks a stream 
develops on each side of it. Such a stream flows between the ice or 
lateral moraine on one side and the hill slope on the other. It may 
degrade or agerade its channel and may bury ice-blocks in its bed. Flow- 
ing from the glacier into a lateral channel, the waters may farther on dis- 
appear beneath theice. Their courses on the rock surface have no head 
nor any end at a local baselevel. When the ice has vanished their beds 
remain as terraces along the slope. Such streams may be seen on mount 
Rainier, adjacent to the stagnant ends of the glaciers, but they there have 
torrential falls. 
An interesting result of corrasion by streams lateral to a former glacier 
is to be seen about 26 miles (42 kilometers) southeast of Seattle, in the 
upper valley of Issaquah creek. The valley is about one-quarter of a 
mile (.4 kilometer) wide and is divided along the middle by a line of 
low hills of drift material. Issaquah creek flows along the southern 
side. A row of swamps occupies an old channel on the northern side, 
and they drain across the valley by gulches through the central hills into 
the southern channel. The interpretation of these relations is that two 
streams developed in parallelism on the northern and southern sides of 
a shrinking glacier. As the ice disappeared they persisted and cut their 
*This description of certain terraces had been written when my attention was called to Salis- 
bury’s definition of kame terraces in the Annual Report of the State Geologist of New Jersey for 
1893, pp. 152 to 156. The definition applies to the terraces here described and the name is accord- 
ingly adopted, without change of statement, 
