Captain Clarke, on quitting the central encampment at _Traveller's Rest Creek_, had marched in a southerly direction, and had traversed a distance of one hundred and sixty-four miles, to the head of _Jefferson's river_. This journey was performed, on horseback, and in six days, over a country by no means difficult; so that, in future, the passage of this elevated region will be divested of a considerable portion of its terrors. He also discovered that the communication between the _Upper Missouri_ and the _Yellow-stone river_, was attended with little trouble; for Gallatin's river, one of the tributary streams of the Missouri, approaches within eighteen miles of the Yellow-stone, and, at a place, where the latter is completely navigable. Being unable to find wood of sufficient magnitude for the formation of canoes, Captain Clarke and his men were obliged to proceed on horseback, about one hundred miles down the side of this river. At length they succeeded in constructing boats, and sailed down the remainder of this stream with great rapidity. On the 27th, at the distance of two hundred miles from the Rocky Mountains, they beheld that elevated region for the last time. The Yellow-stone being easy of navigation, they reached the place of rendezvous earlier than they had expected. The whole party being now assembled below the conflux of the Yellow-stone and Missouri rivers, they prosecuted the remainder of their voyage together; experiencing, in the prospect of home, and in the ease with which they descended the river, a compensation for all their fatigues; and receiving the visits of various tribes of Indians who resided upon its banks. The greatest change which was experienced by them, in their southward progress, was that of climate. They had passed nearly two years, in a cool, open country, and they were now descending into wooded plains, eight or ten degrees further to the south, but differing in heat much more than is usual in a correspondent distance in Europe. They were likewise greatly tormented by musquitoes. On landing at _La Charrette_, the first village on this side of the United States, they were joyfully received by the inhabitants, who had long abandoned all hopes of their return. On the 23d of September they descended the Mississippi to _St. Louis_, which place they reached about noon; having, in two years and nine months, completed a journey of nearly nine thousand miles. * * * * * At St. Louis we shall resume the narrative of Mr. Pike, who, in the month of July, 1806, set out from that place on an expedition westward, through the immense territory of Louisiana, towards New Spain. The chief objects of this expedition were to arrange an amicable treaty between the Americans and Indians of this quarter; and to ascertain the direction, extent, and navigation, of two great rivers, known by the names of Arkansaw and Red River. Eighteenth Day's Instruction. WESTERN TERRITORY CONCLUDED.