134

PAST AND PRESENT CONTINENTS.

[CHAP. washed the northern bases of the Alps; then a much lower and narrower chain than it now is. The site of the present Himalaya was long occupied by the ocean, up to early Tertiary (Eocene) times. The Caspian and the Sea of Aral in Asia are the last remnants of a sea which once occupied a considerable part of Central Asia, and connected these seas with the Black Sea; and the great desert of Sahára in North Africa appears to be the bed of a sea now dried up. Quite recently Mr. W. T. Blanford has shown that the Persian deserts have had a similar history. On the other hand, there are good grounds for believing that the islands dotted so abundantly over the Central Pacific Ocean, and now known as Polynesia, represent the last remnants of a great tract of land, probably a continent, that once occupied that part of the globe and is now submerged; and the same may be affirmed of a part of the Indian Ocean, viz. that which is occupied by the groups of coral islands referred to in Chapter VI.

The greater part of the land of the globe is distributed in five great continental masses, viz., Europe-Asia, regarded as it really is, as a single continent; Africa, North and South America, and Australia. The forms of all are mainly determined by the direction and position of their mountain ranges, which form, so to speak, their skeletons, the plains and table-lands around and between them being regarded as appendages to the mountains. The direction and relative position of the principal mountain ranges of Europe-Asia on the one hand, and of the Americas on the other, are strikingly contrasted. In the former continent, the great mountain system and the table-lands that it includes run almost east and west, and occupy the southern part of the continent; while, to the north, extends a great plain, but little elevated above the sea, and indeed in part lying at a lower level. In America, on the other hand, the principal mountain system, that of the Rocky Mountains and the Andes, runs north and south along the western margin of the continents; and from its foot, great plains extend to the eastward, abutting against lower chains near the east coasts

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MOUNTAIN SYSTEMS OF CONTINENTS.

135

of the broader parts of the continents. In both cases the mountains are the older land, and the plains are sea bottoms which, in part, have been elevated in more recent geological times. Some additions to these plains have been subsequently made by rivers, but these are comparatively unimportant.

The structure of Africa is less well known, though much has been added to our knowledge in late years, more especially by Dr. Livingstone, whose death while perseveringly exploring the still unknown regions of the interior, civilizing the people, and endeavouring to redeem them from the shameful traffic in slaves, has added one more illustrious name to the long list of martyrs in the cause of science and philanthropy. On its northern margin the form of Africa is determined by the Atlas range, which runs parallel to the great mountain system of Europe; but on the east coast it is bounded by a chain of mountains and table-lands running north and south, and on the west coast are lesser systems having a similar direction; an elevated but generally plain country lying between.

Australia is too little known to allow of any general description. The chief mountain range borders the east coast; but this is far inferior in height to the great mountains of the larger continents, and includes but one peak, Mount Kosciusko, that ranges above the snow line. On the north and west coasts are hills of inferior elevation, while a great plain extends along the greater part of the south coast.

The great mountain system of the Europo-Asiatic continent, having then an east and west direction, it is to be observed that the continent itself extends farthest in that direction. As far as this great system has yet been examined, (the Alps and Pyrenees in Europe and the Himálaya in Asia), it appears to date from the early part of the Tertiary epoch, and at several subsequent periods it has undergone repeated disturbance, up to late Tertiary times. The low northern plain is of later date, while those inferior chains that lie to the north of the main system, and are distinct from it, the Scandinavian and British mountains, the Thurin

136

STRUCTURE OF EUROPE AND ASIA.

[CHAP.

gian hills, Erz-gebirge and Riesen-gebirge of Germany and the Ural of Russia, are all of earlier origin, in some cases very ancient. To the south of the great mountain axis, a number of peninsulas run out, viz. Spain, Italy and Greece in Europe, and Arabia, India and the Malay peninsula in Asia. Each of these has its mountain ranges; and while certain of them, for instance those of Italy and the Grecian peninsulas, are no older―in part, perhaps, more recentthan the Alpine and Himálayan chains, others, such as India, are of very high antiquity. The present peninsula of India indeed has probably been in the condition of land, or chiefly so, from a very early period, and has doubtless formed part of a continental mass of land, stretching to the south-west and connecting it with Madagascar and Tropical Africa, during ages in which the site of the present Himalaya was covered by the sea. During the earlier part of this period it was also connected with Australia.

The great mountain system of Asia, like that of America, consists of several chains, for the most part parallel to each other or nearly so, enclosing extensive tracts of mountainous land and elevated plains; which, being at a great height above the sea, are termed table-lands. The loftiest of these is Tibet, bounded by the Himálaya on the south, and by a little-known chain, termed on Chinese maps the Kuen Lun, on the north. From the foot of this last, the great sandy desert of Gobi or Shamo, the western and more fertile extremity of which forms the now independent kingdom of Yárkand, extends to the Thian Shan range, and averages 2,000 or 3,000 feet above the sea level. Further to the west, the great low plain of Northern Asia stretches farther south; being separated from Yárkand by the Pamir range or Bámi-dunya, which runs north and south, connecting the western extremity of the Thian Shan with the Himálaya and the Hindu Kho. The plain terminates at the foot of the latter range on the east, and at that of the Elbrouz on the west, in the neighbourhood of the Caspian Sea. To the south of these ranges lies another series of table-lands and elevated plains, viz. the table-land of Afghánistán, with the lower

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PLATEAUX. INLAND SEAS. RIVERS.

137

Seistan plain on the east, and the arid desert plains of Iran or Persia on the west. Proceeding farther in this latter direction, we next come to the lofty plateau of Armenia, 7,000 feet above the sea, extending from the valley of the Kara, at the foot of the Caucasian chain, to the mountains of Kúrdistán, which overlook the upper waters of the Tigris and the low alluvial plain of Mesopotamia. This plain, as Mr. Loftus has shown, was once an extension of the Persian Gulf, and has been formed by the alluvial deposits brought down through many centuries by the above-named river and the Euphrates. Lastly, the peninsula of Asia Minor is formed by the elevated and mountainous plateau of Anatolia, lying between the Taurus on the south along the coast of the Mediterranean, and the Anti-Taurus range on the north, along the margin of the Black Sea.

The upraising of these great plains and plateaux has evidently taken place at the same time as that of the mountain ranges that bound them. The Gobi desert and the plains of Persia and Seistan were for a long period occupied by great lakes or inland seas, like the Caspian and Sea of Aral at the present day. Indeed these two seas, as I have already mentioned, are but the remnants of a far more extensive sea which once occupied the steppes of Southern Russia; but unlike the plains of Persia and Gobi, they lie in a depression of the continent, the surface of the Caspian being eighty-two feet below the level of the

ocean..

We have learned in Chapters VIII. and IX. that the courses and the character of rivers are determined by the form of the surface and the climate, chiefly the rainfall, of the countries that they drain. Let us now observe how these facts apply to the case of Asia. And here it is first to be noticed, that while winds from the west, the prevailing direction in Northern Asia,1 have to traverse Europe, before reaching it, they can bring but little vapour, except when they blow from the Mediterranean or the Black Sea, or See Chapter II., p. 31.

138

WINDS AND RAINFALL.

[СНАР.

unless in their course they pass over the Caspian; and in the two former cases, they must cross the mountains of Asia Minor and the Caucasus, which drain them of much of their vapour. Winds from the south-east, that is to say, from the seas of China and those still farther south, are certainly warm and moist, and as a consequence, the plains and hills of China, over which they blow, are well watered and fertile. Still more is this the case with the greater part of India and the Malay peninsula, which are exposed to the wind blowing from tropical seas, and during the southwest monsoon receive an abundant rainfall. But in Arabia, where the prevalent winds appear to be from west or east, these have to traverse either the desert country of the Lower Nile, or the almost equally arid plains and the mountains of Persia and Bálúchistán. The Red Sea and the Persian Gulf are too narrow to furnish much vapour, and this little condenses as rain on the mountains of Arabia, so that no drop ever falls on the burning sea of loose sand, the Dahna, which covers the greater part of its surface. Now the southerly winds from Indian seas, and the south-easterly winds from the China seas, must traverse the great mountain system of the Himálaya and Tibet, or the lower but still lofty mountains of China, before they can reach Central Asia; and, as we have seen in previous chapters, whatever vapour they carry is deposited as snow on the cold lofty slopes of these great chains. Consequently Central Asia is exceedingly dry, and in great part absolutely rainless, like Arabia. The winds, which, in the spring months more especially, blow thence towards Europe, are consequently dry winds and very cold; for the winter cold of Central Asia and Eastern Siberia is more intense than that of any part of the world under the same latitudes. The reason of this cold has been already explained in former chapters.1

Since, then, the rainfall is very heavy on the south-east of the continent, and very small or altogether wanting in the interior, we should expect to find the largest rivers in the former region; not necessarily the longest, for their I See pp. 28 and 51.