GEOLOGY-LOWER COLUMBIA-WILLAMETTE VALLEY. 
57 
of the wood is very well preserved, and, upon microscopic examination, seems identical with 
that of the Douglass spruce now growing on the same surface. 
Below the Cascades, and on the western skirts of the Cascade mountains, the river is in some 
places bordered by tertiary strata, which I had no opportunity of examining. The hills and 
mountains adjacent to the stream below seem to be still, as above, composed of trap and meta- 
morphic slates. 
THE COUNTRY BORDERING- THE LOWER COLUMBIA. 
GENERAL FEATURES. 
The parallelism between the valleys traversed by the Sacramento and the San Joaquin and 
that traversed by the Willamette and Cowlitz has been before alluded to. This parallelism is 
much more complete than might be inferred simply from the general similarity of figure. If, 
as seems inevitable from the facts that have been stated, the Sierra Nevada and Cascade range 
form portions of the same mountain chain, the two great valleys—those of Oregon and Cali¬ 
fornia—are bounded on the east by the same wall. The Coast mountains of Oregon, as has 
also been stated, exhibit a remarkable similarity in their physical features and in geological 
structure with those of California, and we have every reason to believe that they form a continu¬ 
ation f the same chain. The sandstones and shales, which, with trap, are the only rocks 
exposed on the lower Columbia, and that portion of the Willamette valley which I examined, 
contain but few fossils, resembling in that respect, as well as in their lithological features, the 
sandstones and shales so characteristic of the coast ranges in the vicinity of San Francisco. 
Near the mouth of the Cowlitz they contain beds of lignite of greater thickness than in any 
part of California which I visited ; and the sandstones near Astoria have yielded a large number 
of fossils, which have been described by Mr. Conrad in the geology of the exploring expedition, 
and pronounced by him to be of Miocene age. 
LOCAL GEOLOGY. 
WESTERN SLOPE OF CASCADE MOUNTAINS. 
While I descended the Columbia, two detachments of our party crossed the Cascades to the 
Willamette valley. Of these one, under the command of Lieutenant Williamson, passed south 
of the Three Sisters, crossing the summit something more than 150 miles south of the Columbia, 
following down the middle fork of the Willamette to its junction with the main stream. 
The other, under command of Lieutenant Abbot, crossed by a pass discovered by him just south 
of Mount Hood. From the gentlemen connected with these parties I received much valuable 
information, and specimens illustrative of the geology of that portion of the range which they 
traversed. From Lieutenant Williamson I learned that the entire mass of the chain at the 
point where he crossed it is composed of the same trappean and metamorphic rocks that have 
been noticed as constituting the geology of the region about the Three Sisters. No stratified 
rocks were met with before reaching the lower portions of Willamette valley, where the tertiary 
sandstones are largely developed, and by erosion have formed hills several hundred feet in alti¬ 
tude. These sandstones, with masses of vesicular trap, were the only rocks which he noticed 
in traversing the valley. 
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