I subjoin an analysis of the soil in the river bottom near Fort Hall, which will be of assistance in enabling you to form some correct idea of its general character in the neighboring country. I characterize it as good land, but the analysis will show its precise properties.
Silicina ----------------- 68.55 Alumina ------------------- 7.45 Carbonate of lime --------- 8.51 Carbonate of magnesia ----- 5.09 Oxide of iron ------------- 1.40 Organic vegetable matter -- 4.74 Water and loss ----------- 4.26 ______
Our observations place this post in longitude 112° 29' 54", latitude 43° 01' 30", and the elevation above the sea, 4,500 feet.
Taking leave of the homeward party, we resumed our journey down the valley, the weather being very cold, and the rain coming in hard gusts, which the wind blew directly in our faces. We forded the Portneuf in a storm of rain, the water in the river being frequently up to the axles, and about 110 yards wide. After the gust, the weather improved a little, and we encamped about three miles below, at the mouth of the Pannack river, on Lewis's fork, which here has a breadth of about 120 yards. The temperature at sunset was 42°; the sky partially covered with dark, rainy clouds.
23d.--The temperature at sunrise was 32°; the morning dark, and snow falling steadily and thickly, with a light air from the southward. Profited of being obliged to remain in camp, to take hourly barometrical observations from sunrise to midnight. The wind at eleven o'clock set in from the north-ward in heavy gusts, and the snow changed into rain. In the afternoon, when the sky brightened, the rain had washed all the snow from the bottoms; but the neighboring mountains, from summit to foot, were luminously white--an inauspicious commencement of the autumn, of which this was the first day.
24th.--The thermometer at sunrise was 35°, and a blue sky in the west promised a fine day. The river bottoms here are narrow and swampy, with frequent sloughs; and after crossing the Pannack, the road continued along the uplands, rendered very slippery by the soil of wet clay, and entirely covered with artemisia bushes, among which occur frequent fragments of obsidian. At noon we encamped in a grove of willows, at the upper end of a group of islands about half a mile above the _American falls_ of Snake river. Among the willows here, were some bushes of Lewis and Clarke's currant, (_ribes aureum_.) The river here enters between low mural banks, which consist of a fine vesicular trap-rock, the intermediate portions being compact and crystalline. Gradually becoming higher in its downward course, these banks of scoriated volcanic rock form, with occasional interruptions, its characteristic feature along the whole line to the Dalles of the Lower Columbia, resembling a chasm which had been rent through the country, and which the river had afterwards taken for its bed. The immediate valley of the river is a high plain covered with black rocks and artemisias. In the south is a bordering range of mountains, which, although not very high, are broken and covered with snow; and at a great distance to the north is seen the high, snowy line of the Salmon river mountains, in front of which stand out prominently in the plain the three isolated rugged-looking mountains commonly known as the _Three Buttes_. Between the river and the distant Salmon river range, the plain is represented by Mr. Fitzpatrick as so entirely broken up and rent into chasms as to be impracticable for a man even on foot. In the sketch annexed, the point of view is low, but it conveys very well some idea of the open character of the country, with the buttes rising out above the general line. By measurement, the river above is 870 feet wide, immediately contracted at the fall in the form of a lock, by jutting piles of scoriaceous basalt, over which the foaming river must present a grand appearance at the time of high water. The evening was clear and pleasant, with dew; and at sunset the temperature was 54°. By observation, the latitude is 42° 47' 05", and the longitude 112° 40' 13". A few hundred yards below the falls, and on the left bank of the river is an escarpment from which we obtained some specimens.