Although these Cordilleras of North America afford access by their dislocations to a great supply of mineral substances, they are on the whole a curse to the continent. By the cold and dryness which their height entails, they reduce one third of the continent to sterility. Though here and there in their valleys we find oases of fertile land, and many regions of limited area may be made fertile by the use of irrigation, at least nineteen-twentieths of their lands are irretrievably barren. When their resources of precious metals are exhausted, as is likely to be the case within a hundred years, they will probably be to a great extent abandoned by man. Only the extreme northern section and a part of the central and border lands afford any other attractions to settlers than is found in their mineral wealth.
West of the Cordilleras of North America we have a narrow and mountainous coast region that is abundantly watered by the moisture from the Pacific, which penetrates some distance into the land over the lower ridges that border on them. Although this belt of fertile country cannot be compared in populationsustaining power with the Atlantic coast region, it is of great fertility, and has a climate of surpassing excellence.
On the borders of Mexico, within the limits of the United States, the mountains sink down to much less extreme heights, and the climate becomes less strenuous. This region is better fitted for the permanent occupation of man; but only a small part of the land is arable,—probably not one-tenth of its surface is or ever will be fit for the plough.
In Mexico proper we have a country that retains the character of the Cordilleras so far as its general elevation is concerned, but loses the lofty ridges which we find farther to the north. The loss of these barriers, combined with the narrowing of the space between the Atlantic and the Pacific waters, and its more southern position, increases the temperature and the rainfall; so that the fertility of the country augments in a rapid way as we go southwards, until finally in the isthmic part of the continent we have a tropical luxuriance of life. The lowland borders of the country gain upon the width of the table-land, until south of the Tehuantepec Isthmus the whole region is essentially unfit for the uses of our race.