This swell, starting from the eastern base of the Rooky mountains in about i lat. 50° N., runs eastward, separating the waters which fall into the Arctic ocean and Hudson bay from those which find their way into the gulf of Mexico. So gradual is the rise that we can define its summit only by noticing whether the general course of the streams is northward or southward. This low swell divides the continent of North America east of the Rocky mountains into two nearly equal parts the northern half of which is almost all incapable of cultivation. A little west of the head of Lake Superior this swell divides. One branch sweeps southeastward, the other northeastward, forming between them the basin of the lakes whose waters pass through the St. Lawrence into the Atlantic. So slight is the elevation of the southeastern watershed that a canal with no cutting of more than 100 feet would open an outlet for the waters of Lake Superior, Michigan, Huron, and Erie into the Mississippi, and thence to the gulf of Mexico, instead of into Ontario, and through the St. Lawrence into the northern Atlantic. The lake basin of North America is thus closely connected with that of the Mississippi. Between the eastern slope of the Rocky mountains and the western slope of the Appalachian range lies the basin or valley of the Mississippi. This is in some respects the most notable on the globe.

Its area is about 1,250,000 sq. m., being only exceeded in extent by the valley of the Amazon. Latitude, elevation, and rainfall combine to render every part of it capable of supporting a dense population. Next to it in this respect comes the basin of the Plata in South America. The most striking physical feature of the basin of the Mississippi is its uniform plain-like character. From the mouth of the river to its sources there is nothing like a mountain. At its junction with the Missouri it is but 381 ft. above the level of the sea; at its source in Lake Itasca it is 1,680 ft., the average descent for the whole distance being less than eight inches to the mile. Its great affluent, the Missouri, from Fort Benton to the junction, falls only ten inches to the mile. The Ohio, from Pittsburgh to its mouth, falls less than five inches to the mile. The Red river falls a little more than a foot, the Arkansas not quite two feet to the mile. Except on its exterior rim, the basin drained by the Misissippi and its main branches falls less than six inches to the mile. The consequence is that there are no rapids to obstruct navigation, each river being navigable as far as the depth of water will permit. The entire navigable length of these rivers is about 40,000 m.

The hydrography of the remaining regions of North America is of little consequence, the Rio Grande being the only other river of any importance upon the eastern side. - With the exception of purely tropical productions, North America has nearly every species of grain, fruit, and vegetable. It has given to the eastern continent maize, which next to rice is the cereal which enters most largely into human consumption, directly as an article of food, and indirectly as sustenance for animals. - North America is rich in nearly every valuable mineral. Iron is so widely diffused, especially within the United States, that it may be considered universal. Copper is found in many localities, the most abundant deposits being in the region of Lake Superior. Gold and silver have been found in every part of the Rocky mountain and Appalachian chains, the deposits in Mexico, California, and the adjacent regions probably exceeding those of all the rest of the globe. Lead is found in various parts, the main locality, probably the most productive in the world, being in Illinois, Iowa, Missouri, and Wisconsin. Quicksilver has hitherto been found chiefly in Mexico and California, where the mines equal in productiveness those of Austria. Zinc has been found only within a limited area, mainly in New Jersey and Pennsylvania. Tin is the only valuable metal which does not occur in large quantities.

The coal fields of North America comprise more than seven eighths of all known to exist. Those already explored exceed the entire area of Great Britain. Salt is widely diffused, the principal saline springs being in New York, Virginia, and Michigan. Petroleum, which may properly be classed among mineral substances, abounds within a comparatively limited area, the central point being in northern Pennsylvania, thence extending northward and westward. - Politically North America is divided into British America, the United States, and Mexico. British America occupies the whole northern half, with the exception of Alaska, the extreme northwestern angle, formerly Russian America, but now by purchase belonging to the United States. It is bounded N. by the Arctic ocean, E. by Davis strait and the Atlantic, S. by the United States, and W. by Alaska and the Pacific (where its shore line is very narrow, only about 350 m.). Its entire area is about 3,500,000 sq. m.; but with the exception of a border on the St. Lawrence and the lakes, and a very narrow strip on the Red river, and a portion on the Pacific, the whole of British America lies north of the line of cultivation. The population is 4,455,000, of which the larger part are of European descent.

Nearly all of habitable British America is now consolidated as the Dominion of Canada. - The United States occupy the central part of North America, from the Atlantic to the Pacific. They are mainly bounded N. by British America (Alaska occupying an isolated position), S. by Mexico, E. by the Atlantic, and W. by the Pacific. The total area, including Alaska (580,107 sq. m.), is about 3,600,000 sq. m. The population by the census of 1870 is 38,558,371, of whom 33.589,377 are white, 4,880,000 colored, 63.254 Chinese, and 25,731 settled Indians. - Mexico is bounded N. by the United States, E. by the gulf of Mexico and the Caribbean sea, W. by the Pacific, and S. by Central America. It has an area of nearly 800,000 sq. m., and a population estimated in 1808 at 9,173,052, of whom more than half are set down as Indians, and only about 1,000,000 whites, the remainder being of mixed blood and negroes.