54 
GEOLOGY—THE BASIN OF THE COLUMBIA. 
LOCAL GEOLOGY. 
The trough of the Columbia at the Dalles is similar, in all its general features, to the canons 
of the streams which traverse the Des Chutes basin. The banks which bound it are less abrupt 
and further removed from the channel; but this difference is, doubtless, due to the absence of 
the thick bed of overlying trap which protects the softer marls from erosion, and forms the pre¬ 
cipitous walls which enclose the Des Chutes. Layers of trap occur, however, at several points 
in the slopes of its banks, which are very noticeable to any one descending to the stream, but 
they are of less thickness and less continuous than those of which I have spoken. 
The Dalles of the Columbia are formed by one of these beds of trap, through which the stream 
cuts in deep and narrow channels, which have received the name of Dalles. Directly opposite 
the village, the north bank of the river presents the mural edge of a layer of trap which is 
partially columnar, and continuous for some miles. Although so much modified by the erosion 
to which I have referred, the banks of the Columbia, at the entrance to the great canon which 
traverses the Cascades, are formed of sedimentary deposits, which were once continuous over all 
the area now occupied by the valley through which it flows ; and, although these strata have 
been somewhat disturbed, I think we have conclusive evidence that they have been eroded, by 
the deepening of the bed of the stream, to a point two thousand feet below their upper 
surface. The area about the entrance of the canon of the Columbia corresponds in every essential 
particular to those which are drained through the several canons of Pit river, the Klamath, and 
the Des Chutes. Whatever has been said, therefore, in reference to those areas, the sedimentary 
deposits which occupy them, and the canons formed by their draining streams, is equally appli¬ 
cable to the basin of the Columbia ; and if its structure has not at once suggested its history to 
those who have examined it, it is doubtless because, from its magnitude, it could hardly be 
viewed as a whole, and it was necessary to come to its study through similar but smaller basins, 
which could, with all their relations, be taken in at one view. 
In all these basins the sedimentary deposits, so accurately stratified over such large areas, 
prove the presence and agency of water of considerable depth. The deeply cut canons through 
which they are drained must have been worn by streams which commenced their work of erosion 
many hundred, sometimes two or three thousand, feet above their present beds. The nature of 
the sediments deposited by this water proves that it was fresh. Among the great number of 
specimens of deposits known or suspected to be infusorial, collected in Oregon or California, and 
sent to Prof. J. W. Bailey for examination, were some from Monterey,-from Shoal water bay 
in Washington Territory, and several other points on the coast. With these were represen¬ 
tatives of the infusorial marls of the different basins of Pit river, the Klamath, the Des Chutes, 
and the Columbia. 
A short time previous to the death of this eminent microscopist, he indicated to me the results 
of his first examination of these specimens ; and, although the localities were but imperfectly 
known to him, I was much interested to observe that, while the infusorial deposits of Monterey 
were marked as containing marine forms, and others on or near the coast as containing mingled 
marine and fiuviatile forms, every specimen collected east of the Cascades, or Sierra Kevada, 
was said to contain only “fresh water Diatomacece.” It is a little remarkable that, in these great 
accumulations of stratified sediments, many of them fine, and indicating the tranquillity of the 
water in which they were deposited, I was able to discover no other fossils than the infusoria 
referred to ; nor did I find any other organisms but the imperfectly preserved plants of Psuc- 
see-que creek ; the only intelligible vegetable remains being trunks of coniferous trees. From 
