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 cailons 

 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 fluviatile forms, every specimen collected east of the Cascades, or Sierra Nevada, 

 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 



