The Missouri _Reporter_ of the fourteenth instant contains a notice of the expedition of Lieutenant Fremont, of the United States Topographical Engineers, to the base of the Rocky Mountains, in the latitude of the Platte and Kanzas rivers, with a view to ascertain positions and localities, to explore the face of the country, and to make the government fully acquainted with that remote and important point of our extended territory now becoming of so much greater interest from the extension of our trade to the northern parts of Mexico and California, and the settlement growing up in the valley of the Columbia River. The line of communication now followed by immigrants, traders and travelers to the Columbia and California, is upon this route, and through the famous South Pass—a depression in the Rocky Mountains at the head of the River Platte, which makes a gate in that elevated ridge, passable in a state of nature, for loaded wagons, of which many have passed through. This examination of the country on this side of the Rocky Mountains comes at a very auspicious moment to complete our researches in that direction, and to give more value to the surveys and examinations of the Columbia River, its estuary, and the surrounding country, made by Lieutenant Wilkes in his recent voyage, and of which a full report has been made to the government. These two examinations will give us an authentic and interesting view of the important country belonging to the United States on each side of the Rocky Mountains; and taken in connection with the great scientific survey of Mr. Nicollet, commencing at the mouth of the Missouri River, and extending north to the head of the Mississippi, and to latitude 49°, and covering all the country in the forks of these two rivers, over an extent of ten degrees of latitude, will shed immense light upon the geography and natural history of the vast region west of the Mississippi River.—_Globe_. The following is the article from the Missouri _Reporter_: Lieutenant Fremont, of the corps of the topographical engineers, left here under orders from the war department, about ten days ago, with a party of twenty men on a tour to the Rocky Mountains. The object of the expedition is an examination of the country between the mouth of the Kanzas and the headwaters of the great River Platte, including the navigable parts of both these rivers, and what is called the Southern Pass in the Rocky Mountains, and intermediate country, with the view to the establishment of a line of military posts from the frontiers of Missouri to the mouth of the Columbia River. This expedition is connected with the proposition now before congress to occupy the territory about the Columbia River as proposed by Dr. Linn’s bill.