In the treaty of amity and commerce, eleven years afterward, it was agreed that a line drawn from Lake of the Woods overland to the source of Mississippi should be the boundary. But, alas! the sources of the Mississippi for fifty years afterward proved as difficult a problem as the source of the Nile. In the first decade of this century it was impossible to draw the southern line of Rupert's Land. The United States during this period evinced some anxiety in regard to this boundary, and, as we shall see, a number of expeditions were despatched to explore the country. The sources of the Mississippi naturally afforded much interest to the Government at Washington, even though the convention of London of 1818 had settled the 49 deg. N. as the boundary. The region west of the Mississippi, which was known as Louisiana, extended northward to the British possessions, having been transferred by Spain to the United States in 1803. A number of expeditions to the marches or boundary land claim a short notice from us, as being bound up with the history and interests of the Hudson's Bay Company. LEWIS AND CLARKE'S EXPEDITION. Of these, a notable and interesting voyage was that of Captains Meriwether Lewis and William Clarke, of the United States army. This expedition consisted of nearly fifty men--soldiers, volunteers, adventurers, and servants. Being a Government expedition, it was well provided with stores, Indian presents, weapons, and other necessary articles of travel. Leaving Wood River, near St. Louis, the party started up the Missouri in three boats, and were accompanied by two horses along the bank of the River to bring them game or to hunt in case of scarcity. After many adventures the expedition, which began its journey on May 14th, 1804, reached the headquarters of the Mandan Indians on the Missouri on October 26th. The Mandans, or, as they have been called, the White Bearded Sioux, were at this time a large and most interesting people. Less copper-coloured than the other Indians, agricultural in habit, pottery makers, and dwelling in houses partly sunk in the earth, their trade was sought from different directions. We have seen already that Verendrye first reached them; that David Thompson, the astronomer of the North-West Company, visited them; that Harmon and others, North-West traders, met them; that fur traders from the Assiniboine came to them; that even the Hudson's Bay Company had penetrated to their borders. The Mandans themselves journeyed north to the Assiniboine and carried Indian corn, which they grew, to Rupert's Land to exchange for merchandise. The Mandan trail can still be pointed out in Manitoba.