In the extent of its navigable rivers, the difference is proportionately large. The Mississippi and its tributaries constitute a continuous channel for steam navigation of 12,000 miles in extent, which would be nearly doubled by reckoning the length of the navigable channels at the period of high water. The river system of the Mediterranean, Euxine, and the Caspian, to which may be added that of the Nile, will not together exceed 5000 miles, or less than half the length of navigable channels of the American system. The natural advantages of the Mediterranean of America may be summed up as follows: with double the productive area, it has capacity for a greater variety of products, by reason of its variety of climate; it has double the extent of navigable rivers, which pour their bounties into the same sea; and not only are the rivers and continents tributary to this region, but the ocean currents and winds, converging at the same point, bring the products of the Orient to exchange for those of the New World. In a letter addressed to Mr. Rockwell, M. C., at that time secretary of the special committee to whom was referred a resolution of Congress, asking for information respecting routes to the Pacific, Lieut. Maury has, with signal ability and in not too glowing language, sketched the future of the American Mediterranean, (which is destined to surpass its European prototype,) whose fine harbors will become the marts of an opulent trade and the centers of a higher standard of civilization. These desirable ends will be greatly accelerated by the intermarine canal between the two seas, by which the trade of China and Japan may meet the commodities of Europe— “Argosies of stately sails, Pilots of the purple twilight, dropping down with costly bales,” and the products brought down by the Mississippi and the Amazon into the Gulf of Mexico. CHAPTER IV. Effect of the Canal on the Interest of the Valley of the Mississippi—Pacific Railroad as a Rival of the Isthmean Canal—Rates of Freight on Ocean, Lakes, Rivers, Canals, and Railroads—San Francisco and the Trade of China and Japan—Considerations of General Interest—Probable Revenue.