PRESENT MINOR. TOPOGRAPHIC FORMS. 125 
The alluvial cone and deltas of the White River system, filling the 
Duwamish valley and extending to the Puyallup valley, are thus seen 
to be indicative of stability of sealevel during the epoch of their develop- 
ment. This epoch is postglacial. Its duration may perhaps be estimated 
within fairly close extremes if the rate of delta expansion shall be deter- 
mined for both Elliott and Commencement bays. There is independent 
evidence which might appear to contradict the inferred stability of sea- 
level, and which consists in cut terraces and small deltas of brooks occur- 
ring atsome height above sea. These features were pointed out by Rus- 
sell, who at the time interpreted them as records of post-Pleistocene 
submergence and uplift marked by two terraces, one at approximately 80 
feet (20 meters), the other at 20 feet (6 meters) above the present sea- 
level. Observations made subsequently in the Duwamish valley indicate 
that the terraces above 60 feet (18 meters) are records of ponded waters 
which gathered during the epoch of latest glacial retreat. I shall discuss 
them more fully in that connection. The terrace at 20 feet above sea is 
probably wave-cut and records an uplift of that amount. 
Sea-cliffs and benches—The shores of the Sound generally present bold 
profiles, which in some instances result from landslides, but more exten- 
sively are sea-cliffs. The heights of the cliffs are functions of the steep- 
ness of the original slopes in which the facets are cut. They vary from 
10 feet (3 meters) to 300 feet (90 meters). The bench extending from 
the bases of the cliffs out below tide is defined by the steeper grade, 
which begins at a depth of 1 to 2 fathoms (1.8 to 3.6 meters). It varies 
in width from 150 feet (45 meters) abreast of the promontories to 1,000 
feet (300 meters) or more in the little bays. Off the headlands the bench 
is probably for nearly its full width cut into the drift slope; in the bays 
it is largely or wholly built out. Spits and bars of characteristic forms 
also occur along the shores, but the great depth of the waters and the 
slight power of the waves render the growth of such features extremely 
slow. 
FEATURES OF THE EPISODE OF LATEST GLACIAL RETREAT 
Nature of glacial accumulation.—Before proceeding to any description of 
the drift phenomena it is necessary to state a conclusion which follows 
unequivocally from several lines of evidence. The Puget Sound basin 
was repeatedly occupied by glaciers flowing from three directions, nam ely, 
from the east, from the west, and from the north. The western system 
descended the short eastern slope of the Olympic range, and havine but 
a limited area of accumulation was probably of least volume of the three. 
The eastern system occupied the valleys in the western slope of the Cas- 
cade range from the Skagit valley to the Cowlitz valley. It was larger 
in area than the western system and included the glaciers of mount 
ee 
