There is no line, straight or crooked, suitable for a national boundary upon which to divide. Trace through, from east to west, upon the line between the free and slave country, and we shall find a little more than one-third of its length are rivers, easy to be crossed, and populated, or soon to be populated, thickly upon both sides; while nearly all its remaining length are merely surveyors' lines, over which people may walk back and forth without any consciousness of their presence. No part of this line can be made any more difficult to pass by writing it down on paper or parchment as a national boundary. The fact of separation, if it comes, gives up on the part of the seceding section the fugitive-slave clause, along with all other constitutional obligations upon the section seceded from, while I should expect no treaty stipulation would ever be made to take its place. But there is another difficulty. The great interior region bounded east by the Alleghanies, north by the British dominions, west by the Rocky Mountains, and south by the line along which the culture of corn and cotton meets, and which includes part of Virginia, part of Tennessee, all of Kentucky, Ohio, Indiana, Michigan, Wisconsin, Illinois, Missouri, Kansas, Iowa, Minnesota, and the Territories of Dakota, Nebraska, and part of Colorado, already has above 10,000,000 people, and will have 50,000,000 within fifty years if not prevented by any political folly or mistake. It contains more than one-third of the country owned by the United States--certainly more than 1,000,000 square miles. Once half as populous as Massachusetts already is, it would have more than 75,000,000 people. A glance at the map shows that, territorially speaking, it is the great body of the Republic. The other parts are but marginal borders to it, the magnificent region sloping west from the Rocky Mountains to the Pacific being the deepest and also the richest in undeveloped resources. In the production of provisions, grains, grasses, and all which proceed from them this great interior region is naturally one of the most important in the world. Ascertain from the statistics the small proportion of the region which has as yet been brought into cultivation, and also the large and rapidly increasing amount of its products, and we shall be overwhelmed with the magnitude of the prospect presented. And yet this region has no seacoast--touches no ocean anywhere. As part of one nation, its people now find, and may forever find, their way to Europe by New York, to South America and Africa by New Orleans, and to Asia by San Francisco; but separate our common country into two nations, as designed by the present rebellion, and every man of this great interior region is thereby cut off from some one or more of these outlets, not perhaps by a physical barrier, but by embarrassing and onerous trade regulations.