MARGINAL FEATURES OF THE VASHON DRIFT. 139 
left free to push farther in this direction than it could have extended 
except in the lee of high ridges. 
From lake Tapps to Carbonado the relief of this marginal zone is not 
regular. Where Fennel creek flows southward its course is determined 
on the west by a ridge which is a lateral moraine of the ice-tongue that 
filled the Puyallup valley. Over Orting hill the drift is irregularly heaped, 
though broadly ridged on trends which descend steeply northwest. Be- 
tween Carbon river and South Prairie creek the relief presents the char- 
acter of transverse ridges, which may be called kame moraines of various 
stages of retreat. They are associated with pitted plains and delta for- 
mations and alternate with stream channels. 
West of Puyallup valley to Tacoma the Vashon drift is characteristic- 
ally heaped and ridged northeast of Steilacoom plains. West of Orting 
a notch is cut in the plateau scarp where it turns from south to southeast. 
The Vashon drift extends south to the notch and forms a ridge above 
the 500-foot contour thence southwest for 4 miles (6 kilometers). <A 
till composed of materials from mount Rainier extends northward to the 
600-foot contour. A washed gravel plain lies in a triangular space be- 
tween the two kinds of drift. From the southern limit thus defined, the 
Vashon drift extends northward in a zone .5 mile to 1.5 miles (.8 to 2 
kilometers) wide. On the east, next to the plateau scarp, its relief is 
irregular; kettleholes and mounds confusedly mark an elevated margin. 
South by west from Puyallup a depression, with strongly terraced slopes, 
extends through the marginal zone to the plains. From this hollow west 
beyond Tacoma the relief is characterized by strong gravel ridges, which 
trend from north to south. They are very conspicuous on the highland 
southwest of Tacoma. They are of the same type as those which have 
been described as occurring northwest of the Wilderness and about lake 
Tapps, and, like them, they run in a course which is transverse, not 
parallel, to the limits of the Vashon drift. 
In each of the localities in which the marginal zones with transverse 
ridges are strongly developed the Vashon driftis spread upon high ground, 
with relatively lower surfaces beyond in the direction of ice movement. 
Subglacial streams flowed longitudinally to the ice in the direction of 
the transverse ridges. It is inferred that the effect of running waters in 
modeling the under surface of the ice and in transporting drift beneath 
the ice determined the marginal drift type. 
Following Chamberlin’s genetic classification of Pleistocene glacial for- 
mations,* the marginal forms just described fall technically under two 
*T. C. Chamberlin ; ‘‘ Proposed genetic classification of Pleistocene glacial formations.”? Journal 
of Geology, vol. ii, No. 5, 1894. 
