The public domain north of latitude 42 deg., through which it lies, comprises about seven hundred thousand square miles,--a territory larger than England, Ireland, Scotland, France, Spain, Portugal, Belgium, Holland, all the German States, Switzerland, Denmark, and Sweden. The route surveyed by Governor Stevens runs north of the Missouri River, and crosses the mountains through Clark's Pass. Governor Stevens intended to survey another line up the valley of the Yellow Stone; and Lieutenant Mullan commenced a reconnoissance of the route when orders were received from Jeff Davis, then Secretary of War, to disband the engineering force. THE ROUTE. Recent explorations indicate that the best route to the Pacific will be found up the valley of this magnificent river. The distances are as follows:--From the Mississippi above St. Paul to the western boundary of Minnesota, thence to Missouri River, two hundred and eighty miles, over the table-land known as the Plateau du Coteau du Missouri, where a road may be constructed with as much facility and as little expense as in the State of Illinois. Crossing the Missouri, the line strikes directly west to the Little Missouri,--the Wah-Pa-Chan-Shoka,--the _heavy-timbered_ river of the Indians, one hundred and thirty miles. This river runs north, and enters the Missouri near its northern bend. Seventy miles farther carries us to the Yellow Stone. Following now the valley of this stream two hundred and eighty miles, the town of Gallatin is reached, at the junction of the Missouri Forks and at the head of navigation on that stream. The valley of the Yellow Stone is very fertile, abounding in pine, cedar, cotton-wood, and elm. The river has a deeper channel than the Missouri, and is navigable through the summer months. At the junction of the Big Horn, its largest tributary, two hundred and twenty miles from the mouth of the Yellow Stone, in midsummer there are ten feet of water. The Big Horn is reported navigable for one hundred and fifty miles. From Gallatin, following up the Jefferson Fork and Wisdom River, one hundred and forty miles, we reach the Big Hole Pass of the Rocky Mountains, where the line enters the valley of the St. Mary's, or Bitter Root Fork, which flows into the Columbia. The distance from Big Hole Pass to Puget Sound will be about five hundred and twenty miles, making the entire distance from St. Paul to Puget Sound about sixteen hundred miles, or one hundred and forty-three miles shorter than that surveyed by Governor Stevens. The distance from the navigable waters of the Missouri to the navigable waters of the Columbia is less than three hundred miles. CHARACTERISTICS OF THE LINE.