American geography may be said to have had three important problems to solve, in modern times. The first and second of these, related to the source of the Missouri, and to the course and termination of the Columbia. Both, were substantially resolved by the expedition of Lewis and Clark, under the administration of Mr. Jefferson. It is to be borne in mind, however, that but one of the three forks, up to which the Missouri was traced, has been explored, that its two northwestern branches have not been ascended, and that, consequently, we do not actually know, which of its primary tributaries is the longest, or brings down the greatest volume of water. The true source of the Mississippi, which forms the third topic of inquiry, was brought into discussion at the same period. And immediately after the acquisition of Louisiana, the American government sent an officer, with a suitable body of men, to determine it. Lieut. Pike, who was selected for this service (who, nine years afterwards lost his life as a general in the service, at the taking of York) did not, however, set out early enough in the season (1805) to accomplish the object. After the selection and purchase of the site, on which the fort near the Falls of St. Anthony, is now situated, he encountered delays in ascending the rapids characteristic of that part of the Mississippi. Winter overtook him before reaching the junction of the De Corbeau. He prepared for its severities by erecting a block house, for the security of his provisions and men. He then proceeded with a small detachment, on snow shoes to Sandy Lake, and Leech Lake; two points of central influence, which were then occupied by the North West Fur Company. As the partners of this company consisted of foreigners, and their operations were continued after the legal transfer of the country to the American government, Lieut. Pike would have been justified in making a seizure of the valuable furs then in their possession. He did not, however, adopt this course, and exhibited a magnanimity in relation to it, which is in accordance with his subsequent acts of disinterested intrepidity. He collected the geographical data, which are embodied in his published map and journal, and returned from his wintry station, on the opening of navigation in the spring.