DISTRIBUTION AND CHARACTER OF THE PLATEAUS. 115 
ing abruptly to alluvial plains and to the waters of the sound. As benches 
along the mountain spurs they fringe the Cascade and Olympic ranges 
up to 1,200 feet (860 meters) above sea, locally. Toward the axis of the 
sound their altitudes vary from 400 to 500 feet (120 to 150 meters) above 
sea. In any one district they are approximately of uniform height, and 
viewed as a whole constitute the surface of the vast drift mass with which 
the basin is partially filled. 
There is no map which satisfactorily represents the distribution of 
these plateau-shaped masses. Their boundaries against the Cascades and 
Olympics have not beensurveyed. Their outlines as defined on the charts 
of the sound are incomplete, since the coastline extends from one mass 
to another wherever the intervening hollow is filled with alluvium in- 
stead of water. Thus Des Moines island is merged with the mainland, 
although physiographically it is isolated by the Duwamish valley, which 
is the homolog of Hood canal. The northeastern extremity of the 
Olympic peninsula is divided by a similar depression which connects 
Hood canal with the strait of Fuca. The Great peninsula is likewise 
separated into island-like masses by lowlands which connect the reentrant 
bays. 
The plateau masses between the mainland on the east and the main- 
land on the west, thus isolated by depressions filled with water or allu- 
vium, are of long and narrow forms, with major axes trending north and 
south in general. The trends are not uniform, however. On the west 
they diverge southwestward and on the east they depart southeastward, 
giving the sounds a pear-shaped form, of which the entrance to Admiralty 
inlet is the stem. 
The margins of the plateaus along the tops of the slopes are wavy, but 
in details entire, in the sense that the edge of a leaf is said to be entire. 
They are but rarely and not deeply incised by streams. The outlines 
along the slopes at water level have been modified by waves, which have 
cut away portions and built out spits. 
THE HOLLOWS, THEIR DISTRIBUTION AND CHARACTER 
Interrelations—Admiralty inlet extends from the southeastern end of 
the strait of Fuca 58 miles (93 kilometers) south by east, with an average 
width at sealevel of 3.5 miles (5.6 kilometers). Itis the trunk of an un- 
symmetrical labyrinth of hollows, which ramify 40 miles (64 kilometers) 
ina course of south by west, with a width of but 1.5 miles (2.4 kilometers). 
Duwamish valley is the southeastern member. It trends southeast and 
south 35 miles (56 kilometers), and is about 2 miles (3.2 kilometers) wide. 
It is partially filled with alluvium. Between Admiralty inlet and Hood 
canal are many hollows, locally deeper than sealevel, and elsewhere shal- 
