in great force, in various parts of the globe, is perhaps altogether unheeded by many individuals. And thus

Some souls there are that live, and breathe, and die,

Scarce knowing more of Nature's potency,

Than what they learn from heat, or cold, or rain,

Or sad vicissitude of weary pain.

Volcanos and the movements of great earthquakes are confined to certain districts of the earth, a circumstance which has led an eminent geologist to designate the tracts where they more especially occur, as volcanic regions, or volcanic bands. These volcanic regions are continuous tracts, marked by the occurrence, at intervals, of active volcanic vents, often constituting mere spots, thinly scattered over the surface of vast districts, but presenting abundant evidence that subterranean fire is at work in the intermediate spaces, by the earthquakes which from time to time take place. Gaseous vapours also are plentifully disengaged from the soil; petroleum, and other bituminous substances, sometimes issue from the ground in great abundance; whilst thermal or hot springs often occur, possessing a very high temperature, and it not unfrequently happens that the temperature of springs is raised after earthquakes, even in districts distant from active volcanos. These volcanic regions, or bands, appear to have a general correspondence with the direction of the most elevated land in the districts they traverse. Thus, in Europe and Asia, the volcanic band runs parallel to the grand mountain ranges of those regions; and in America, it extends along the line of the mighty Andes. In more scattered volcanic groups, such as the Polynesian volcanic region, we usually find one island forming a central focus; of this the island of Hawaii forms an instance.

The principal volcanic regions, or bands, are those extending from the Caspian Sea to the Azores; from the Aleutian Isles to the Moluccas; and the volcanic region of the Andes. To these may be added, though of inferior importance, the African volcanic region, and the Icelandic volcanic region.

15

CHAPTER III.

GENERAL DISTRIBUTION OF LAND AND WATER.-MOUNTAINS, VALLEYS, PLAINS.—TABLE OF HEIGHTS OF MOUNTAINS, ETC.

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 portions 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.

sea.

The remaining portion of the dry land consists of islands of various dimensions, and of various elevation above the 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 vast range. The greatest length, however, of Africa is from north to south; and although the interior of this portion of the globe, is still too much involved in obscurity for any certain conclusions to be formed, yet, from the general direction of the rivers, and from the notices of travellers, there is much reason to infer, that a range of mountains more or less interrupted, extends from Abyssinia towards the southern extremity of 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.

Whilst 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 the direction of mountain ranges usually accords with that of the greatest extension of land, in all regions where they occur, whether of large or small dimensions; the length of mountain ranges is therefore

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

C

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 enclosing between their ridges either elevated table-lands or deep valleys.

It rarely happens that both sides of mountain ranges present a similar character, one declivity being usually much steeper and more abrupt than the other, a circumstance which has considerable influence upon the temperature on the opposite sides of mountains. The declivities are generally steepest where great depressions occur, and accordingly, when mountains abut on the sea, we find their steepest slopes are most frequently presented to that side. Thus, the ridges of the Scandinavian mountains, and those of Greenland, both present their boldest escarpments to the North Atlantic Ocean. The lofty ridge of the Atlas gradually declines towards the Sahara, or Great Desert, but is very abrupt on the northern side, where

Mauritania's giant shadows frown

From mountain cliff to coast descending sombre down. The mighty range of the Andes has generally a gradual slope on its eastern declivity, but presents a series of rugged precipices to the Pacific, in some parts strikingly bold and abrupt.

Isolated or detached mountains are usually of volcanic origin. In some instances these attain a great elevation, of which Etna, Ararat, the Peak of Teneriffe, and Mowna Roa form examples; but the loftiest summits generally form parts of extensive mountain ranges; and a reference to the table at the end of this chapter will show that the most elevated mountains of Europe occur in the Alps, those of Asia in the Himalaya Mountains, and those of America in the Andes.

In describing mountain ranges, it is usual to adopt some