every citizen of the country, to open for them new and national highways. From this digression, embracing facts and views which seemed essential to an intelligent discussion of the main subject, we pass on to examine the Appalachian outlet by which the great Western empire of America may find its way to the sea. The bird's-eye view here presented will show the Appalachian mountain-chain, and the waters which thread their way along its gentle slopes eastward to the Atlantic basin and westward to the Ohio and Mississippi Valleys. The Alleghanies bear a striking geographic resemblance to the Highlands of Scotland, so famed in song and story. Like the central Grampian Hills--those majestic buttresses in whose recesses the old Caledonians found secure and impregnable asylums from the Roman legions--except that they are richer in verdure and less lofty, they form the grand natural rampart of the American Union. To use the words of Lavallee, the French military historian and statistician, "Mountains play the principal part in military operations: true ramparts of states, they interrupt the development of strategic movements, and render the greatest efforts necessary for their passage and possession. They are the poetical part of the theatre of the art of war." If the day ever comes, as come it may, when the kingly powers of the world combine to crush the republican institutions of the United States, and swarm the harbors and bays of our Atlantic seaboard with their allied navies, the defiles of the Alleghanies will prove the Thermopylaes of the Union; and against their eastern base the surging wave of invasion must be stayed, if stayed at all. Like the Scottish peaks, The grisly champions that guard The infant rills of Highland Dee, or the Spanish wall of the Pyrenean chain, on whose Sierras, in 1808, Wellington's blazing lines of Torres Vedras arrested Massena's march, the mountains that look out on our Atlantic sea-front must ever be of the highest military importance. To throw across their central ridges a great aqueduct is no mean undertaking of merely local significance, but may take rank with the old Roman aqueducts, with the magnificent roads constructed by Napoleon over the Alps, and with the more modern and now triumphant tunnels through Mont Cenis and the Hoosac Mountains, and the rapidly-progressing railway over the Andes from Callao to the Amazon Valley.