and on the Age of the Cascade Mountains. 169 
Nor is this thickness very exceptional for the lava of the 
Cascade Range. We have already said that the higher points 
of the lava cliffs of the Columbia cafion for near fifty miles 
are not less than 2,0U0 feet. But, in order to make this clearer, 
we will take another section which we examined, at some dis- 
tance both from the axis of the range and from the Columbia 
River, viz: the Des Chutes River section. 
The Des Chutes River is a large tributary of the Columbia, 
which, rising in southern Oregon, flows northward, parallel to 
the Cascade Range on the east side and at a distance from its 
axis of at least fifty miles. The region lying between the crest 
of the Cascade and the Des Chutes River is mountainous; but 
this mountainous region stops suddenly at the river, and 
beyond stretches, as far as the eye can reach, a nearly level luva- 
covered plain. Right along the line of contact between the 
mountain and the plain, the river has cut for itself, for more 
than 100 miles, a deep, extremely narrow gorge (fig. 1, a, }, c) 
Des Rae Hill. see 
m 
whole height, from the river bed to the top of Des Chutes hill, 
the edges of lava layers outcrop. I do not know the precise 
height of this hill above the river, but it cannot be less than 
1000 feet. I believe it is nearer 3,000 feet. Here then we 
ave again, at a point 50 miles distant from the axis of the 
Tange and 80 miles from the Columbia River, a clear section 
of pte lava 2,000 to 3,000 feet thick, and the bottom not yet 
rece, 
Beyond the Des Chutes, a nearly level lava plain, covered 
only with northern drift, stretches awa eastward for 30 or 40 
miles. This plain is intersected in Aid directions with deep, 
Narrow stream-gorges, which do not reach the bottom of the 
