CHAPTER III.

GENERAL DISTRIBUTION OF LAND AND WATER.-MOUNPLAINS.-TABLE OF HEIGHTS OF

TAINS,

VALLEYS,

MOUNTAINS, ETC.

So high as heaved the hills, so low

Down sank a hollow bottom, broad and deep,

Capacious bed of waters.

MILTON.

ON referring to the map of the world, we cannot fail to be

struck with the unequal distribution of land and water on its surface, and with the large proportion covered by the waters of the ocean. The whole superficies of the globe (speaking in round numbers) is equal to 197,000,000 square miles nearly; of this the land does not occupy much more than 52,000,000 square miles, or little above one-fourth part : whilst the ocean covers an area of more than 144,000,000 square miles. We shall further observe that the proportion of dry land is much greater in the northern than in the southern hemisphere. The Antarctic regions are, however, too little known for any certain conclusion to be drawn respecting the relative proportions.

The sea occupies the cavities or depressions on the surface of the globe, separating and surrounding the more elevated portion of the earth's crust. The dry land may be arranged under two principal heads-continents and islands. The term continent has been applied to four portions of the earth, and it is common to speak of the continents of Europe, Asia, Africa, and America; but more correctly there are only two continents-two vast and detached portions of the globe-the Old World and the New World; nay, in fact, these are but larger islands, though, on account of their vast extent, and the different natural phenomena presented by continental and insular surfaces, it will be highly desirable to distinguish these divisions of the earth by the designation of continents.

The remaining portion of the dry land consists of islands of various dimensions, and of various elevation above the sea.

Australia so greatly exceeds in size all other islands, that it has been ranked as a continent, but is, perhaps, with greater propriety, included among the islands; it may, however, in conjunction with the numerous smaller islands with which the Pacific is studded, be regarded as a distinct division of the globe. This is sometimes distinguished by the appellation Oceanica.

The general disposition of the land will be observed to differ greatly in the Old and New Continents. In the Old World, especially in that portion which comprehends the divisions of Europe and Asia, the principal extension is from east to west; whilst in the New World it is from north to south. In both cases, this extension is in the direction of the principal mountain ranges. Thus, in the Old Continent, a continuous, or nearly continuous line of mountains, extends from the borders of Europe, on the Atlantic, to those of Asia, on the Pacific Ocean. In Africa, the mountain ranges are less known. The Atlas range, which stretches in the same direction as the great European and Asiatic line, is considered to form a portion of that mighty system. A chain of mountains is also supposed to extend from east to west across this vast peninsula at its greatest breadth, within a few degrees north of the Equator, whilst, to the south of that line, the mountain ranges appear to take a general direction from north to south in accordance with the form of Southern Africa.

This general correspondence between the form of the land and the direction of mountain ranges, is more strikingly exemplified in America, where the Rocky Mountains, and the elevated districts of Mexico, in the northern, and the stupendous Andes in the southern hemisphere, pursue, in a remarkable manner, the general direction of the New Continent. The same character is observable in smaller portions of land, and also in islands, the form of which usually coincides with that of their principal mountain ranges. This is well illustrated in the Dofraveldt Mountains in Scandinavia, in the Apennines in Italy, and in the islands of Japan, Sumatra, &c.

While considering the general configuration of the land,

we may further observe, that in those portions abutting on the great basin of the Atlantic, the proximate sides of the Old and New Continents appear as though they were, in some measure, mutually influenced by the forms of each other. Thus, the coast of Brazil, which forms the principal eastern projection of South America, is almost opposite to the vast African bight, or bay, which extends from Cape Palmas to Cape Negro; whilst the great western projection of Africa is counterbalanced by the basin of the Caribbean Sea and the Gulf of Mexico; and the south-western trending, or stretching out of the coasts of Europe, is answered by the receding of the opposite shores of North America.

The dry land is elevated into mountains and highlands, spread forth in plains, or depressed into valleys, all varying in extent and in elevation above the level of the sea; with one exception, however, a large area occurring in Central Asia, including the Caspian Sea and the Lake of Aral, which is below the level of the ocean.*

The immense basin, which is occupied by the waters of the ocean, is apparently diversified in its surface like the dry land, the submarine valleys forming the deep and fathomless abysses of the sea, whilst the summits of the mountains constitute islands; the shores of the latter being more or less abrupt, according to the character of the oceanic mountains rising above the surface of the waters.

We have already seen that in all mountainous regions, whether of large or small dimensions, the direction of the axis, or principal range, usually accords with that of the greatest extension of land; the length of mountain ranges is therefore generally very great in proportion to their width. They often consist of one grand central range, from which branches or ridges of inferior elevation diverge at right angles; whilst from the latter, smaller lateral branches or spurs again extend, forming hills; and these usually gradually diminish in height until they are lost in the plains. Mountain ranges of considerable elevation are also occasionally met with, running parallel with each other, and

*Recent investigations have shown that the level of the Caspian Sea is 101 feet lower than that of the Euxine, or Black Sea.