The great River Platte is the most direct line of communication between this country and the mouth of the Columbia, and that route is known to be practicable and easy. It therefore becomes important to ascertain the general character of that river and the adjacent country, and the facilities it will be likely to afford in prosecuting contemplated settlements in Oregon. This Southern Pass, or depression in the Rocky Mountains, is near the source of the extreme branch of the River Platte, and affords an easy passage for wagons and other wheel carriages, which have frequently passed over the mountains on that route without difficulty or delay; and it is important that the latitude of this point should be ascertained, as it is thought that it will not vary much from the line established between the United States and Mexico by treaty with Spain, 1819. If this pass should fall south of that line (the forty-second degree of north latitude) it may become necessary to examine the country north of it, the line of the Yellowstone and south branch of the Columbia would, it is thought, afford the next best route. Lieutenant Fremont, though young, has had much experience in surveys of this kind, having made the topographical survey of the Des Moines River, and having assisted the scientific Mr. Nicollet in his great survey of the Upper Mississippi. He is well supplied with instruments for making astronomical observations; for fixing the longitude and latitude of important points; and a daguerrotype apparatus for taking views of important points and scenes along the route; and, if not obstructed in his operations by large bands of wild, wandering Indians, which sometimes trouble small parties passing through that region, may be expected to impart much valuable information to the government and to the country. Since the attention of the country has been directed to the settlement of the Oregon Territory by our able senator (Doctor Linn), and by the reports of those who have visited that region in person, the importance of providing ample security for settlers there, and of opening a safe and easy communication from the western boundary of Missouri to the Columbia River has been universally admitted.