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.
Millions of square miles of arable lands are intersected by rivers of unrivaled extent. The Mississippi, rising in such proximity to the northern lakes as to make their shores tributary to the trade of its valley, flows through twenty degrees of latitude before reaching the Gulf of Mexico. The Amazon, nearly at right-angles with the Mississippi, developing its course chiefly in longitude, bears the varied products of its valley to the ocean, where the equatorial current makes it tributary to the Caribbean Sea. The Amazon is more directly connected with this sea by the Orinoco, with which it is united by the Rio Negro. Humboldt surveyed the channel joining the two rivers, and ascertained the feasibility of a navigable channel between them at high water.
The different positions of the main commercial arteries of the two continents—the one extending through temperate latitudes, the other through tropical longitudes—supply the greatest variety of commodities for commercial interchange. The Mediterranean system, finding its most extensive development in longitude, is limited in the variety of its products by the climatic uniformity of one zone. While American rivers flow through twenty-five degrees of latitude, the European rivers of the Mediterranean extend through but ten degrees.
Berghaus’s map supplies data for a comparison of the river system of the two great continent-bounded seas of the Eastern and Western Hemispheres:
| SQUARE MILES. | ||||
| Area of the Mississippi | basin, including the basins of its tributaries |  | 2,231,000 | |
| the Missouri,Ohio, Arkansas, Red River, etc. | ||||
| Rio del Norte | 180,000 | |||
| South American basins |  | Magdelina | 72,000 | |
| Orinoco | 250,000 | |||
| Amazon | 1,512,000 | |||
| Entire area of basins which drain into the Gulf of Mexico | ||||
| and Caribbean Sea | 4,245,000 | |||
| SQUARE MILES. | |
| European, Euxine, and Caspian | 1,890,000 |
| Basin of the Nile | 520,000 |
| Area of basins of the Mediterranean rivers | 2,410,000 |
Area of basin of the river system of the Gulf of Mexico and the Caribbean Sea is 4,245,000 square miles, a productive area nearly double that of the Mediterranean, which it exceeds by 1,835,000 square miles.
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.