Thus in its main features the valley of the Amazons, like that of the Mississippi, is a cretaceous basin. This resemblance suggests a further comparison between the twin continents of North and South America. Not only is their general form the same, but their framework, as we may call it,—that is, the lay of their great mountain-chains and of their table-lands, with the extensive intervening depressions,—presents a striking similarity. Indeed, a zoölogist, accustomed to trace a like structure under variously modified animal forms, cannot but have his homological studies recalled to his mind by the coincidence between certain physical features in the northern and southern parts of the Western hemisphere. And yet here, as throughout all nature, these correspondences are combined with a distinctness of individualization which leaves its respective character, not only to each continent as a whole, but also to the different regions circumscribed within its borders. In both, however, the highest mountain-chains, the Rocky Mountains and the Western Coast Range, with their wide intervening table-land in North America, and the chain of the Andes, with its lesser plateaux in South America, run along the western coast; both have a great eastern promontory, Newfoundland in the Northern continent, and Cape St. Roque in the Southern: and though the resemblance between the inland elevations is perhaps less striking, yet the Canadian range, the White Mountains, and the Alleghanies may very fairly be compared to the table-lands of Guiana and Brazil, and the Serra do Mar. Similar correspondences may be traced among the river-systems. The Amazons and the St. Lawrence, though so different in dimensions, remind us of each other by their trend and geographical position; and while the one is fed by the largest river-system in the world, the other drains the most extensive lake surfaces known to exist in immediate contiguity. The Orinoco, with its bay, recalls Hudson’s Bay and its many tributaries, and the Rio Magdalena may be said to be the South-American Mackenzie; while the Rio de la Plata represents geographically our Mississippi, and the Paraguay recalls the Missouri. The Parana may be compared to the Ohio; the Pilcomayo, Vermejo, and Salado rivers, to the river Platte, the Arkansas, and the Red River in the United States; while the rivers farther south, emptying into the Gulf of Mexico, represent the rivers of Patagonia and the southern parts of the Argentine Republic. Not only is there this general correspondence between the mountain elevations and the river-systems, but as the larger river-basins of North America—those of the St. Lawrence, the Mississippi, and the Mackenzie—meet in the low tracts extending along the foot of the Rocky Mountains, so do the basins of the Amazons, the Rio de la Plata, and the Orinoco join each other along the eastern slope of the Andes.