KAME TERRACES. 1133 
channels below its bed. A central ridge remained, but it was cut across 
by branches of the southern stream, which captured the northern. 
The following notes describe some of the benches whose characteristics 
indicate their origin as extramorainal or lateral stream terraces of this 
type, which Salisbury has called kame terraces. 
Along the eastern side of the Duwamish valley east of Kent and thence 
northward the upper margin of the slope which rises to the plateau is 
terraced at elevations ranging from 385 to 440 feet (117 to 134 meters) 
above sea. The benches extend in sections along the slope for short dis- 
tances of a mile or two. They are floored with sandy loam, which is 
sometimes gravelly. They are frequently higher along the margin next 
the valley and swampy toward the inner side. They are bounded on the 
east by a more or less abrupt slope of gravelly till 30 to 50 feet (9 to 12 
meters) high. They represent short courses of streams, which flowed be- 
side the Vashon glacier as it shrank from its expansion on the plateaus 
into the banks of the Duwamish valley. They therefore antedated the 
condition of ponded waters in the valley when the sandy deltas formed 
at lower levels. 
The vicinity of Carbonado, where occur the high level deltas already 
described, presents other terraces attributable to Carbon river, acting 
in immediate proximity to the Vashon ice-front. These terraces extend 
from Carbonado northeastward and eastward around the lobe of drift 
deposits to and beyond Wilkeson. Not only Carbon river but also 
Gale creek and South Prairie creek modelled them in conjunction with 
the ice. At Carbonado the surface is cleared of forest and details are 
laid bare. <A terrace whose upper surface is a wide flat, now at an alti- 
tude of 1,175 feet (858 meters) above sea, faces westward with a steep 
bank 25 feet (7 meters) high. It is composed of sand and coarse gravel, 
with boulders up to 2 feet (.6 meter) in diameter of rocks characteristic 
of the Vashon till. The materials are here heterogeneously mingled, 
there interstratified, and elsewhere the coarse gravel is washed clean. 
Precisely similar accumulations of gravel and sand characterizetthe upper 
valley of Carbon river, proceeding from the present glacier. The mate- 
rials forming the upper terrace at Carbonado were in part at least car- 
ried forward in the furthest advance of the Vashon glacier and subse- 
quently swept back by the river in an early stage of the retreat. The 
westward face of this terrace is steep at Carbonado, and is probably a 
cut bank along whose foot the river flowed northward. ‘he ice was 
close by on the west and north. 
At the foot of the upper terrace face is a wide flat of sandy alluvium 
under a thin veneer of pebbles and boulders. The elevation of this 
level at the depot at Carbonado is 1,150 feet (850 meters). It is there- 
— SS 
