144 B. WILLIS—DRIFT PHENONENA OF PUGET SOUND. 
though advancing. After the glaciers became confluent and rose to a 
thickness of 2,000 feet (600 meters) above sealevel, subglacial channels 
developed beneath their combined mass, and in these channels the Vashon 
osars formed. 
Osceola clays.—Blue-gray clays of the aspect and compact character of 
the Osceola till, but unlike it in being stratified, occur between 650 and 
700 feet (200 and 213 meters) above sea,in the bluffs which form the 
north bank of Carbon river, 2 to 3 miles (3 to 5 kilometers) below Car- 
bonado. The deposit is very evenly stratified in horizontal layers, which 
differ slightly in proportions of clay and very fine sand and weather out 
as ribs on the vertical face. The formation oxidizes to a deep brown 
color and assumes the aspect of a carbonaceous clay at a distance, but 
it contains no vegetal remains. It is also free from pebbles. 
This clay was deposited in quiet water. Upon its even upper surface 
the Vashon ice spread subglacial gravels. The clay apparently imme- 
diately antedated the expansion of the ice-sheet over this area. It is of 
local distribution only, and the waters in which it was deposited were 
not extensive. They could have been ponded only by an ice-front on 
the north. The character of the materials identifies it with the Osceola 
till, which was spread by the Cascade glacier at higher levels than this 
to the northeastward and subsequently at lower levels to the northward 
of this occurrence. ‘Thus this clay is correlated with that stage of advance 
of the Vashon and Cascade ice-sheets when they enclosed a water body 
between their fronts and the hills to the south and southeast. 
Along the plateau face on the east side of Duwamish valley beds of 
blue stratified clay underlie the Vashon drift. The highest exposure 
was noted 3.5 miles (5 kilometers) north of Kent, at an elevation of 310 
feet (94 meters) above sea; the lowest was seen 5 miles (8 kilometers) 
south of Auburn, 105 feet (82 meters) lower, or 205 feet (62 meters) above | 
sea. It is not to be inferred that there isa uniform sheet of glacial clay 
100 feet (80 meters) thick extending over a wide area. In the advance 
of the Vashon glacier waters were ponded at various levels, and the sep- 
arate ponds received similar sediments successively. Of these the south- 
ern occurrence on Carbon river is probably the latest. Sand and gravel 
deposits formed contemporaneously with these clays and may occur at 
the same horizons. 
Similar clays occur at much lower levels and are correlated with the 
preceding or Admiralty epoch of glaciation. 
Douty gravels.—Beneath the Osceola clays in the section exposed in the 
northern bank of Carbon river is a deposit of gravel between 600 and 655 
feet above sea. This may be designated the Douty gravels, the station 
of Douty in the canyon near Carbonado being the nearest point having 
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