Glacial Phenomena in Washifigton. — Daivson. 205 
ence to the country rocks. The rocks of the great Cascade 
upheaval, so far as now observable in Okanogan county, west 
of the Okanogan river, are almost entirely crystalline. These 
rocks compose the west bank of the Columbia* river from 
Wenatchee to the mouth of the Okanogan. The east bank, 
on the contrary, throughout this course, presents an un- 
broken escarpment of basalt rising 2000 feet high, which ter- 
minates the big bend plateau on the west. This is the edge of 
the lava sheet; and although the crystalline rocks do at places 
crop out from beneath on the east bank, they are always cov- 
ered thickly with the basalt capping. The river, wliose former, 
more direct course lay far to the eastward, was pushed over 
against the granite by the advancing lava flood, and its future 
course was prescribed by the western limits of the lava; and, 
as Bailey Willis has well pointed out, the course from old 
Ft. Spokane to the mouth of the Okanogan was determined 
by the resultant line of depression between the north-bound 
flow of the Big Bend region, and the south-bound flow, which 
covers the present Colville Indian reservation. 
Then as to its minor topographical features: we find in 
this county, and especially in the lower mountain ranges, a 
numbei of peculiar valleys, deep and narrow, called coulees 
commonly pronounced "cool'ies." This name is applied to 
such valleys, whether short or extensive, as are unoccupied, 
or at least not adequately occupied by running water, and 
have comparatively level floors. Toat's coulee, with its de- 
pendencies in the northern part of the county; x\ntoine coulee, 
from the Methow to the Columbia; Knapp's and Navarre's 
coulees, which cut through the range between lake Chelan and 
the Columbia, may be cited as examples. The problem of 
coulee formation ofifers one of the most inviting subjects 
which we shall attempt to discuss in this paper. 
Scarcely less noteworthy features of this region arc the 
terraces which line the principal streams. Those along the 
Columbia river are about 300 feet above the stream, and at 
favorable points along the river present a surface of several 
square miles. The Okanogan river, likewise, is terraced 
throughout its length. The terraces of the more rapid streams, 
owing to the varied character of their gorges, are more ir- 
regular and infrequent. 
