30th.--Our journey to-day was short. Passing over a high plain, on which were scattered cedars, with frequent beds of volcanic rock in fragments interspersed among the grassy grounds, we arrived suddenly on the verge of the steep and rocky descent to the valley of the stream we had been following, and which here ran directly across our path, emerging from the mountains on the right. You will remark that the country is abundantly watered with large streams, which pour down from the neighboring range.
These streams are characterized by the narrow and chasm-like valleys in which they run, generally sunk a thousand feet below the plain. At the verge of this plain, they frequently commence in vertical precipices of basaltic rock, and which leave only casual places at which they can be entered by horses. The road across the country, which would otherwise be very good, is rendered impracticable for wagons by these streams. There is another trail among the mountains, usually followed in the summer, which the snows now compelled us to avoid; and I have reason to believe that this, passing nearer the heads of these streams, would afford a much better road.
At such places, the gun-carriage was unlimbered, and separately descended by hand. Continuing a few miles up the left bank of the river, we encamped early in an open bottom among the pines, a short distance below a lodge of Indians. Here, along the river the bluffs present escarpments seven or eight hundred feet in height, containing strata of a very fine porcelain clay, overlaid, at the height of about five hundred feet, by a massive stratum of compact basalt one hundred feet in thickness, which again is succeeded above by other strata of volcanic rocks. The clay strata are variously colored, some of them very nearly as white as chalk, and very fine-grained. Specimens brought from these have been subjected to microscopical examination by Professor Bailey, of West Point, and are considered by him to constitute one of the most remarkable deposites of fluviatile infusoria on record. While they abound in genera and species which are common in fresh water, but which rarely thrive where the water is even brackish, not one decidedly marine form is to be found among them; and their fresh-water origin is therefore beyond a doubt. It is equally certain that they lived and died at the situation where they were found, as they could scarcely have been transported by running waters without an admixture of sandy particles; from which, however, they are remarkably free. Fossil infusoria of a fresh-water origin had been previously detected by Mr. Bailey, in specimens brought by Mr. James D. Dana from the tertiary formation of Oregon. Most of the species in those specimens differed so much from those now living and known, that he was led to infer that they might belong to extinct species, and considered them also as affording proof of an alteration, in the formation from which they were obtained, of fresh and salt-water deposites, which, common enough in Europe, had not hitherto been noticed in the United States. Coming evidently from a locality entirely different, our specimens show very few species in common with those brought by Mr. Dana, but bear a much closer resemblance to those inhabiting the northeastern states. It is possible that they are from a more recent deposite; but the presence of a few remarkable forms which are common to the two localities renders it more probable that there is no great difference in their age.