58 
GEOLOGY—WESTERN SLOPE OF CASCADE MOUNTAINS. 
It will be remembered that, when speaking of the glacieal grooves on the western declivity 
of tlie Three Sisters, reference was made to two deep canons, one leading down from Mount 
Jefferson, the other from the Three Sisters, which combined to form a profound gorge leading 
westward, through which a stream flowed, supposed to he a tributary of the Willamette. This 
stream proved to he McKenzie’s fork, and, when crossing it, near its junction with the Willa¬ 
mette, Lieut. W. learned that upon one occasion, and only one, its course had been followed 
from its source. 
Three hunters, having descended to the Willamette in its bed, reported that, throughout its 
entire length, the canon of which I have spoken preserves the character which it exhibits at 
its eastern termination—a deep and narrow gorge, hounded by nearly precipitous walls, from 
which there was no exit hut at the extremities. Its inhospitable nature may he inferred from 
the fact that one of these hunters died from the hardships he encountered in traversing it, and 
the others suffered so severely that they never cared to repeat the experiment. 
This would seem to have been the channel through which the drainage from the glaciers 
had found a passage to the ocean ; and it is not improbable even, from its peculiar angular 
character, that ice occupied some portion of its length. From Mr. Anderson, who accompanied 
Lieut. Ahhot, I learned that the draining valleys leading from Mount Hood have the same 
angular character, and there, as on the slopes of the Three Sisters and Mount. Jefferson, the 
exposed surfaces of the rocks, in many places, exhibit marks of glacial action. 
The minerals brought from Mount Hood are all volcanic, trap, volcanic conglomerate, scoria, 
and ashes. The ashes are white and fine, and closely resemble the marls and tufas of the Des 
Chutes and Klamath basins. They had probably been quite recently thrown out from Mount 
Hood; showers of ashes having been discharged from this mountain several times since Oregon 
has been occupied by the whites. From Mr. Dryer, of Portland, who attempted to ascend 
Mount Hood in 1854, I learned that steam and heated gases were escaping from its summit, 
in many places, at the time of his visit. 
WILLAMETTE VALLEY. 
I was able to examine but a small portion of the Willamette valley in person, as I 
ascended the river only twenty miles from its mouth. The only rock which I saw was the 
tertiary sandstone to which I have alluded, and dark vesicular trap. The sandstone appears 
in the bed and banks of the Willamette at several points below Oregon City. The rock 
over which the river pours at the falls is trap, as are the hills in the vicinity. From the de¬ 
tailed account of the geological structure of the valley above this point, given by Prof. Dana 
in bis geology of the exploring expedition, it appears that the hills bordering the alluvial plain, 
as far south as the Calapooya mountains, are composed of one or the other of the two rocks I 
have mentioned. He represents the sandstones as being not only disturbed, but greatly eroded, 
as at the points examined by Lieut. Williamson. This is not an uninteresting fact, when taken 
in connexion with the evidences of great erosive action which I have cited, and which seem to 
be connected with the existence of glaciers, and may be, in a degree, dependant on the same 
cause. The sandstones of the Willamette valley contain no fossils at the localities where I ex¬ 
amined them, but they exhibit all the lithological characters of the San Francisco group. In 
g ome places they are highly argillaceous, and better deserve the name of'shales than sandstones, 
and not unfrequently contain laminae of gypsum. Near St. Helens, a bed of lignite has been 
discovered, which at one time was supposed to have a high commercial value, but which ha 
