130 B. WILLIS—DRIFT PHENOMENA OF PUGET SOUND. 
composed of cross stratified sands and clays with occasional boulders. 
They probably represent accumulations in channels beneath the ice. 
The absence of a delta corresponding to the Talbot delta may be ac- 
counted for by the assumption that the stream flowed out upon the ice 
and any deposits dropped as it melted. 
Benches in the hard rocks occur south of the Talbot delta and as far 
south as the outlet of Pantherlake. They antedate the terraces in glacial 
and glacio-fluvial deposits, as the latter rest upon them. In hard rocks 
in close proximity to ice gentle slopes tend to extend as flats and steep 
slopes to become precipices under the action of frost. The rocks of the 
Puget Sound basin were long subjected to such sculpture, and these 
benches may with probability be classed as effects of that phase of glacial 
carving. The presence of large blocks of Hocene lignite in till south of 
Kent shows that the Eocene rocks were exposed to glaciation. 
The evidence derived from the study of the deltas and their allied 
forms along the slope of the Duwamish valley indicates that during a 
late phase in the retreat of the Vashon glacier the valley was occupied, 
along its eastern side at least, by waters ponded by the ice. The absence 
of deltas on the western side cannot be positively asserted, but none were 
observed. Their development may have been prevented by ice along 
that bank or limited by the fact that the drainage of the plateau is away 
from the valley tothe southwest. The extent of the ponded waters has 
not been determined. It may have included the Puyallup valley and a 
section of Admiralty inlet. 
Deltas at high levels—Between White river on the northeast, South 
Prairie creek on the south, and the Puyallup river on the west is a tri- 
angular plateau mass of complicated structure, which has a general eleva- 
tion of from 500 to 600 feet (150 to 180 meters) above sealevel. Its apex 
points toward the northwest and its eastern level extends beyond White 
river northeastward. In its northwestern apex the surface of the plateau 
is diversified by long narrow ridges and lakes, which will be described as 
marginal features of the Vashon glacier, produced during a long pause 
in its retreat. They antedate that vanishing phase when it had shrunk 
to an ice-tongue in the Duwamish valley and deposited the lateral mo- 
raines already described. Across its central section from northeast to 
southwest this plateau mass is lowest and has a gentle southern slope. 
Its surface is now a swamp, underlain by till characteristic of the region 
to the eastward and attributed to a glacier which descended from the 
Cascades. This till will be referred to as the Osceola till, as that hamlet 
les in its widest expanse. Fennel creek drains these swamps. On the 
east and south the low marshy level is bounded by a well defined ter- 
race about 100 feet (30 meters) in height. The northern slope and margin 
