South of this domain of northern cold, North America divides itself, by its climate, soil, and topographical reliefs, into the following fairly distinct regions: (1) The eastern lowlands lying between the shore and the Appalachian range; these shade southwardly into (2) the lowlands of the Gulf States, which is the only part of North America in the immediate control of the Gulf Stream. These Gulf lowlands pass northwardly into (3) the great plain of the Mississippi Valley. Between these lowlands of the centre of the continent and the Atlantic sea-coast lie (4) the table-lands and mountains of the Appalachian system. West of the Mississippi Valley lie (5) the region of the Cordilleras of North America; and finally on the western shore we find (6) a narrow region of low mountains, forming a slender fringe of shorelands.
The mountains of the Appalachian system are composed of two parallel series of elevations, an old eastern range of peaks which are worn down to mere shreds; so that in place of being as high as the Alps, as they once were, they have no peaks that rise seven thousand feet above the sea. This outer range is traceable from Newfoundland to Alabama; but it only rises above six thousand feet in the White Mountains of New Hampshire and the Black Mountains of North Carolina. In form these mountains are steep and rugged. Their steep sides hold the little untillable land that exists east of the Mississippi; their actual area is small, for the chain is very narrow, not exceeding a score or so of miles in width, except in the Carolinas and in the White Mountains, where it is somewhat wider. The total untillable area in this chain does not exceed twelve thousand square miles. West of this, the old Appalachian mountain system, separated from it by a broad, elevated, somewhat mountainous valley, lies the newer Alleghany range. This valley intermediate is one of the most fertile and admirably situated in the world; it extends from New Jersey to Georgia, with an average width of about forty miles and a length of about six hundred, having an area of over twenty thousand square miles. The Alleghany Mountains on the west are composed principally of round, symmetrical ridges, often like gigantic works of art, so uniform are their arches; none of them rise to more than five thousand feet above the sea, and their surfaces are so little broken that they generally afford tillable though as yet generally untilled land. Practically no part of this great range, which extends from near Albany to Alabama, is completely unfit for the uses of man, and it includes some of the most fertile valleys of America. The most important feature connected with this double mountain system of the Appalachians is the great area of table-lands which it upholds; these bordering uplands are found all around the mountain system. The greater part of the States of New York, Pennsylvania, Virginia, West Virginia, the Carolinas, Georgia, Tennessee, Kentucky, and Ohio owe the considerable elevation of their surfaces to the table-land elevations bordering the Appalachian mountain system. Taken altogether, this mountain system is perhaps the finest region for the uses of man that the world affords; its great length, of more than fifteen hundred miles from north to south, gives it a range of climate such as would be had in Europe by a mountain chain extending from Copenhagen to Rome. The total area of this Appalachian district, mountains as well as table-lands, is about three hundred thousand square miles. This is an area equal to near thrice the surface of Great Britain.
The Appalachian table-lands fade gradually into the Mississippi Valley. Their distinct character continues to near the borders of that stream where it unites with the Ohio. As we come upon the table-land system of the Cordilleras, soon after we pass west of the Mississippi, this great valley may be considered as made up of the table-lands of two great mountain systems, with only a relatively small area of alluvial matter between the mouth of the Ohio and the Gulf. Unlike the Ganges, the Amazon, and most other great rivers of the first class, the Mississippi River has a small delta section: not over twenty to thirty thousand square miles has this character. By far the greater part of the basin is really table-land, and is thus free from the evil of low countries to a degree equalled by no other very great river basin. Its valley is characteristically a table-land valley, with a general surface of rolling plain, varying from three hundred to five thousand feet above the level of the sea. Outside of the Cordilleras and the Appalachians, this valley has few mountain folds within its ample space. The absence of included mountain systems is almost as noteworthy a feature as the small amount of delta. There are only two or three patches of mountains that lie far beyond the limits of the great mountain systems of the east and west; and only one of these, the Ozark Mountains of Missouri and Arkansas, is at any distance from the main ranges. This is an insignificant group of low hills having considerable geological but no geographical importance.
On the western border of the Mississippi Valley rise the vast ridges of the Cordilleras. This great mountain region is, next after the mountainous area of Central Asia, the most extensive region of great altitude in the world. From Mexico northward this system of mountains widens, until, in the parallel of forty degrees, it has a width of about one thousand miles. This system is made up of many ridges lying upon an elevated table-land. The valleys of the lesser streams are generally over seven thousand feet above the sea; the main peaks, to the number of many hundred, rise over twelve thousand feet above the sea level; many of them attain to about fourteen thousand feet of altitude. Its table-land extends east to near the Mississippi River. The great height and width of this mountain system produce a very marked effect upon the climate of the vast area that it incloses, and upon the country which lies within a thousand miles to the east of its mountain walls. The winds from the Pacific are to a great extent drained of their moisture in the western or Sierra Nevada section of these mountains, and have little moisture to give to the central and eastern chains; and when these winds emerge on to the western plains, they are as dry as those that blow over the Sahara.
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.
The climate of North America south of the divide which separates the streams flowing toward the Arctic Circle from those entering the Atlantic south of Labrador may be said to resemble that of Europe in all important respects. The winters are far colder; but the summer seasons, which determine the usefulness of the soil to man, are as warm and quickening to plants as are those of the Old World. The more considerable cold of winter is a disadvantage, inasmuch as it limits the work of agriculture to a smaller part of the year, and requires a greater expense in the keeping of livestock. This is a considerable evil, especially in the regions north of the parallel of forty degrees; but the cold is not greater than in Northern Germany or in Scotland. There can be no doubt that the body and the mind receive certain advantages from the tonic quality of the winters which compensate for this loss.