The Humboldt and Mexican currents aid the coastwise trade. Thus, by the converging winds and currents, this great intertropical sea seems to be designated by nature as the future commercial center of the world. The two American seas have been styled by Lieut. Maury as the heart of the continent. Its two compartments have been compared to the auricle and ventricle of the human heart, through which, in regular pulsations, by unceasing systole and dyastole, the ocean currents find constant entrance and exit, and circulate through all the world-arteries their vivifying influence. Pursuing the analogy, the two continents, from their general shape and the alimentary part they perform, may not inaptly be compared to the lungs, which convert the blood of commerce into the nutrient and productive elements which contribute to the health and growth of the nationalities of two continents. The rivers having their natural outlet in the Caribbean Sea and the Gulf of Mexico, bring into commercial union two regions producing all the commodities of the globe. The rivers of North America bear to the Gulf the successive harvests of the temperate zone, and receive in return the fruits, woods, dyes, drugs, spices, coffee, cotton, and tobacco of intertropical America. No part of the globe combines so many natural advantages as are found united around this body of water. Its shores present every advantage of soil, climate, vegetation, and convenient harbors likely to attract an enterprising and commercial people. The table lands of Mexico, Yucatan, Guatemala, Honduras, and Columbia afford the most salubrious climate, scenery of the rarest beauty and sublimity, equable temperature, and an endless succession of fruits and harvests. Mountains of perpetual snow look down on plains of unceasing verdure. All that is requisite for the support of life grows spontaneously. The descriptions of Humboldt represent the table lands as suitable to the highest development of the race. One wonders that the tide of immigration, guided by the rational instinct for superior advantages, has not filled every bay and estuary and overspread the plains; or, sweeping down from the north, the Anglo-Americans have not taken possession, as the hardy races of the North of Europe overran the degenerate mixture of nations which overspread the northern shores of the Mediterranean. Those portions of the world which possess the finest climate, whose soil returns the largest yield from the least amount of labor, are held by degenerate and effete representatives of a moribund civilization. In America no alpine barrier interrupts communication with the interior, but an indefinite expanse of plains, prairies, and table lands stretch away to the north, or form broad plateau, as in Central and South America.