continent has not been observed higher than 4300 feet, is on the very summit of Pichincha. Other secondary formations, among which may be mentioned limestone, are also found at greater heights in the New than in the Old world.

With respect to their declivities, it is observed that most of the principal mountains have one of their sides very steep, and the other of a gradual slope. The Alps, for instance, have a much more abrupt descent on the side of Italy than on that of Switzerland; the Pyrenees are steeper towards the south than the north, while the chain of Asturias, which branches westward from the Pyrenees, is just the reverse. Mount Taurus, in the part where it approaches the Mediterranean and the Dardanelles, is abrupt on the south, but in Armenia it has a rapid descent northward. The mountains of Scandinavia are steeper towards the west and north-west, than the south and east; and the Ghauts in Hindustan are in like manner precipitous on the west, and sloping in the opposite direction. With all these chains, therefore, and indeed with most of the chains of the globe, their steepest side is found to be that which approaches most nearly to the sea, and consequently their inclination is most gradual towards the interior of the country in which they are situated.

Mountains in their course commonly make numerous curves and angles; but in most cases the general direction of the principal chains appears almost, if not entirely, to correspond with the greatest length of the continents to which they belong. The Andes in South and the Stony Mountains in North America exemplify this remark; as do also the chains which, with little interruption, pass from the north-eastern point of Asia to the south-west coast of Portugal, and to the western side of Africa. The secondary chains, in the same manner, frequently follow the greatest length of the large peninsulas. This is the case with the Apennines in Italy, the Dovrefield in Scandinavia, the Ghauts in Hindustan, &c.

In order to obtain a connected view

of the loftiest and most extensive system of mountains upon the globe, we must suppose ourselves placed in New Holland with our face turned towards the north; America will then be on the right, Asia and Africa on the left. From Cape Horn to Behring's strait

along the western coast of America, there is an almost uninterrupted range of the highest mountains; from Behring's strait again succeeds an enormous line passing in a south-westerly direction through Asia, leaving China and Hindustan to the south, somewhat interrupted as it approaches Africa, but still to be looked upon as continuing its course in the mountains of Persia and Arabia Felix. From Cape Gardafui in Africa to the Cape of Good Hope, there appears to be a chain which completes the view.

The series of mountains which we have thus followed, is in the form of an immense irregular curve, which comprises within it, the Pacific and Indian Oceans, with their innumerable islands, besides a portion of Asia, including China, the Birman dominions, and the Indian peninsula. It presents a steep face towards these oceans, while, on the other side, the land very generally slopes towards the Atlantic and Arctic Oceans.

The following is a table of the height of some of the principal mountains of the globe, reckoning from the level of

the sea.

The elevations of those in Asia and Africa are far from having been ascertained with accuracy. Some recent measurements make the highest summits of the Himalayan range as much as 28,000 feet; but, though these calculations seem very doubtful, it is not unlikely they are at least 25,000 feet high.

20 or 30 feet in a perfectly regular manner, and, as it were, pushed up by a force beneath-which suddenly exploded with a dull noise, and scattered about a volume of black mud in every direction. After an interval of two or three, or sometimes four or five, seconds, the hemispherical body of mud or earth rose and exploded again. In the same manner this volcanic ebullition goes on without interruption. The spot where it occurs is nearly circular and perfectly level; it is covered only with the earthy particles, impregnated with salt water, which are thrown up from below: the circumference may be estimated at about half a mile. A strong, pungent, sulphureous smell is perceived on standing near the explosion, and the mud recently thrown up is warmer than the surrounding atmosphere. During the rainy season these explosions are more violent."

The mountain of Maccaluba in Sicily, and some hills at the town of Taman in the Crimea, are also distinguished by eruptions of mud.

It is remarkable, that in the Old Continent, the principal chains of mountains contain no volcanoes, and that islands, and the extremities of peninsulas, are alone the seats of these convulsions; while in the New World, the immense range which runs along the shore of the Pacific Ocean possesses more volcanoes than are to be met with in the whole of the Old Continent and its adjacent islands. Professor Jameson has given the following estimate of the number of vol

a complete series of volcanoes may be traced. The Aleutian islands, which stretch from that peninsula to the opposite peninsula of Kamtchatka, possess several. On Kamtchatka, there are some of great violence. The islands of Japan and Formosa have several, and beginning with Sumatra and Java, they are scattered all over that immense Archipelago which forms so remarkable a feature of the Pacific Ocean.

In the Indian Ocean, the Islands of St. Paul, Amsterdam, and Bourbon, have volcanoes in action. The most formidable volcanoes of the Mediterranean are Etna in Sicily, and Vesuvius upon the coast of Naples. Between these two mountains are the Lipari islands, all of volcanic character. The Atlantic Ocean contains several groups of this kind; Iceland has suffered frequently from the terrific eruptions of its volcanoes; the Azores and the Canaries, and some of the West India islands, also experience the effects of subterranean fire.

In some places, parts of the land which are covered by the waters of the ocean are the seats of volcanoes; and it has sometimes happened, that new islands have been formed during submarine eruptions. A recent instance of this kind occurred in 1811, in the neighbourhood of St. Michael, one of the Azores, the small group which lies about 800 miles to the west of Portugal. This new island has since disappeared. It is probable, that some clusters of islands (among which are the Azores, just mentioned, and the Lipari islands north of Sicily) owe their origin to the breaking out of submarine volcanoes.

Several mountains bear evident marks of having at some very distant period been the outlets of fires; and on this account, they are called extinct vol

canoes.

On Valleys and Plains. Valleys are the spaces lying between and their lowest part is commonly the opposite ridges of mountains or of hills, bed of some torrent or river, which originates in the higher grounds. Those between high mountains are in general clefts or fissures. narrow and long, resembling large In some of these it has been observed, that the nooks or valleys, among the Alps and Pyrenees, angles on each side correspond with such exactness to projections on the opposite side, that if it were possible

to exert a force sufficient to bring their sides together, they would fit into each other so closely, that no trace of the opening would remain. Such valleys as these would seem to have been formed by some convulsion of nature. The narrow openings which are the entrance to the high valleys, are called passes or defiles, and these are often of the most gloomy and terrific aspect. Valleys, which are upon a lower level than the class just mentioned, are wider and more soft in their features, and gradually lose themselves in the plains. Plains are likewise of two kinds. Those which are extensive, but very elevated, come under the denomination of table land. There are several plains of this sort; but the most remarkable are those among the Andes*, those of Mexico, and the immense plains in central Asia, to the north and north-east of Hindustan. The great Himalayan and Altaian chains form the ramparts, as it were, of this extensive and desolate table-land, a large proportion of which is the desert of Gobi or Shamo. The low plains, from the nature of their soil, seem formerly to have been covered by the sea. The large plain, to the south of the Baltic, is one out of several instances of this character.

On Islands.

The plains of Quito are 12,000 feet above the level of the sea.

†This word, which is usually but incorrectly written Kobi or Cobi, signifies a naked desert.

close to mountains on shore, they may be considered as a continuation of the latter. The Aleutian isles, which run in a curve south of Behring's strait, connect in this manner the mountains of the New with those of the Old World. In some cases, where a chain of islands extends from one part of the shore of a main land to another, it would appear as if, at a remote period, the sea had overwhelmed a portion of the main land, leaving those spaces uncovered which now form the islands. This seems still more probable if the water on the land side of the chain be not very deep, or if the islands are of a lofty and mountainous character. It has been supposed that, among others, the West India islands and the Archipelago between New Holland and the opposite coast of Asia, were rendered insular by an incursion of the ocean having detached them from the continents to which (if this supposition be just) they formerly belonged.

On Springs and Rivers.

The origin of the numerous springs that break forth from beneath the earth's surface cannot be referred to one excluThe internal reservoirs by sive cause. which they are supplied are, in many cases, derived from the water which the earth absorbs from rains and melted snow ; from these reservoirs, wherever there is uneven or mountainous ground, the water flows out by minute fissures in the sides of the hills. But when we see springs rising up in plains, it is evident that they must have ascended, that is, travelled in a direction contrary to that produced by the force of gravity, in order to reach the surface. This, no doubt, is sometimes to be attributed to water flowing under ground from distant elevations, and to the natural tendency of a liquid to find its level. But the rising up of springs, in plains, cannot always be accounted for in this manner; and it has, therefore, been supposed, that the earth contains capillary tubes, the effect of which, in attracting liquids upwards, is explained in Chapter VIII., of the treatise upon It is also evident that Hydrostatics. such springs as suffer no diminution even from the longest continued dry weather, must be derived from a source quite independent of rains, and other external means of supply. They must, therefore, proceed from some vast body of water within the earth; and it has,

with apparent reason, been concluded, that many springs arise from the ocean filtering through the pores of the earth, the salt particles being lost in the

passage.

Springs, which have their waters combined with mineral substances, and are, from that circumstance, called mineral, are very numerous, and of various kinds. Warm and hot springs are also common, especially in volcanic countries, where they are sometimes distinguished by violent ebullitions. Iceland is noted for these curious phepomena: its celebrated boiling fountain, the great Geyser, frequently throws out its contents to the height of more than a hundred feet, sometimes to twice that elevation.

Rivers are to be traced to springs, or to the gradual meltings of the ice and snow which perpetually cover the summits of all the most elevated ranges of mountains upon the globe. The union of various springs, or of these meltings, forms rivulets: these last follow the declivity of the ground, and commonly fall, at different stages, into one great channel, called a river, which, at last, discharges its waters into the sea, or some great inland lake. The declivities along which descend the various streams that flow into one particular river are called its basin, a term, therefore, which includes the whole extent of country from which the waters of the river are drawn. As mountainous regions abound in springs, we find that most rivers, more especially those of the first class, commence from a chain of mountains: each side of a chain also has its springs, and the rivers which originate on one side flow in the opposite direction to those which rise on the other. As it is the property of water to follow the most rapid descent that comes in its way, the courses of streams naturally point out the various declivities of the earth's surface, and the line from which large rivers flow in contrary directions will generally mark out the most elevated parts of the earth. In European Russia, where the rivers are very extensive, there is, however, a singular exception to this rule, the line which separates the sources of those rivers being very little above the level of the Baltic or of the Black sea. It has been observed by some writers, that the extent of a river is in proportion to the height of the range of mountains from which it descends. This is,

in a certain degree, true, because the greater the bulk of the mountains, the more numerous the springs and torrents which they furnish; but the relation between the extent of a river and the surface of its basin is much closer and more invariable. Even this is not sufficiently comprehensive, for it is evident that the size of a river depends upon three circumstances-the surface of its basin-the abundance or otherwise of that surface in springs-and the degree of humidity possessed by the climate of the region from which it draws its supplies. As many springs, however, are formed by the rains, the second of these circumstances will, in some measure, vary with the last. By an attention to these remarks, the causes of the great size of the South American rivers will be apparent. The peculiar position of the Andes with respect to the plain of that continent,-the fact that by very far the largest proportion of its running waters are drained off in one general direction (towards the Atlantic)—the multiplicity of streams that intersect the country,-and the humidity of the climate, all contribute to that result. The Andes being placed so near the coast of the Pacific, the rivers which flow from them into that ocean are small; while those which flow on the other side, having such an immense space to traverse, are swelled into a most majestic volume before they reach the Atlantic. The physical circumstances of the old continent are unfavourable to the accumulation of such vast bodies of water as the rivers of South America. Europe is not of sufficient extent; Africa is oppressed by a scorching climate, and abounds in sandy deserts; in Asia the atmosphere generally is not so moist, while the more central position for the most part of the great mountainous range of that continent, and the existence of capacious inland lakes*, which are the final receptacles of the streams that fall into them, are the causes why the waters are more equally drained off in different directions than in the New World.

When water, by following a descent, has once received an impulse, the pressure of the particles behind upon those before will be sufficient to keep the stream in motion, even when there is no longer a declivity in the ground. The only effect is, that in passing along a

*The Caspian Sea and Lake Aral,