AUG. 31.--Capt. Lewis, during the absence of his brother-officer, had succeeded in procuring from the Indians, by barter, twenty-nine horses,--not quite one for each man. Capt. Clarke having now rejoined us, and the weather being fine, we loaded our horses, and prepared to start. We took our leave of the Shoshonees, and accompanied by the old guide, his four sons, and another Indian, began the descent of the river, which Capt. Clarke had named Lewis's River. After riding twelve miles, we encamped on the bank; and, as the hunters had brought in three deer early in the morning, we did not feel in want of provisions. On the 31st of August, we made eighteen miles. Here we left the track of Capt. Clarke, and began to explore the new route recommended by the Indian guide, and which was our last hope of getting out of the mountains. During all day, we rode over hills, from which are many drains and small streams, and, at the distance of eighteen miles, came to a large creek, called Fish Creek, emptying into the main river, which is about six miles from us. Sept. 2.--This morning, all the Indians left us, except the old guide, who now conducted us up Fish Creek. We arrived shortly after at the forks of the creek. The road we were following now turned in a contrary direction to our course, and we were left without any track; but, as no time was to be lost, we began to cut our road up the west branch of the creek. This we effected with much difficulty. The thickets of trees and brush through which we were obliged to cut our way required great labor. Our course was over the steep and rocky sides of the hills, where the horses could not move without danger of slipping down, while their feet were bruised by the rocks, and stumps of trees. Accustomed as these animals were to this kind of life, they suffered severely. Several of them fell to some distance down the sides of the hills, some turned over with the baggage, one was crippled, and two gave out exhausted with fatigue. After crossing the creek several times, we had made five miles with great labor, and encamped in a small, stony, low ground. It was not, however, till after dark that the whole party was collected; and then, as it rained, and we killed nothing, we passed an uncomfortable night. We had been too busily occupied with the horses to make any hunting excursion; and, though we saw many beaver-dams in the creek, we saw none of the animals.