An Account of Expeditions to the Sources of the Mississippi, and through the Western Parts of Louisiana, to the Sources of the Arkansaw, Kans, La Platte, and Pierre Jaun, Rivers; Performed by Order of the Government of the United States during the Years 1805, 1806, and 1807, and a Tour through the Interior Parts of New Spain, when Conducted through These Provinces, by Order of the Captain-General, in the Year 1807