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greater the mass and the elevation of the mountain, the less frequent and more tremendous are the eruptions. Stromboli, the small volcano on one of the Lipari islands, is almost always burning; 11,430 Vesuvius has more frequent eruptions 10,735 than Etna; while the immense summits 9,600 of the Andes, Cotopaxi, and Tungu6,500 rahua have an eruption hardly once in 9,600 a century. The volcanoes of America, 9,600 besides the common lava and rocks, &c., cast out scorified clay, carbon, sulphur, and water, accompanied, in some instances, by fishes. 13,000 The eruption the most astonishing, 11,200 11,980 perhaps, of any upon record is that 12,180 which, in April 1815, issued from the Tomboro mountain in Sumbawa, one of the islands of the Indian Archipelago 21,425 (see Notes to chap. i. of Raffles History 19,633 of Java); and we mention it, in order to 19,136 give an idea of the violence which some18,867 times characterises volcanic agency. 17,376 The tremulous motions which the ground 18,324 underwent, during this eruption, were 15,931 felt throughout a circular space of near13,437 ly 2000 miles in diameter, and the report 9,542 of the explosions was heard over an 17,720 equally extensive area. Within its more 15,705 immediate range, embracing a space of 13,275 300 miles around it, it excited the great12,195 est alarm. On Java, at the distance of 8,633 300 miles, the sky was overcast at mid8,314 day with clouds of ashes, the showers of 5,756 which covered every thing to the depth 6,650 of several inches; and explosions were 7,278 heard, at intervals, like the report of 17,863 14,736 artillery or the noise of distant thunder. On Sumbawa itself thousands of individuals were destroyed by the fury of the eruption.
(NOTE) Those marked are volcanoes. And † are the highest points of the range to which they belong.
The term Volcano (derived from VULCANUS, the name which the Romans gave to their imaginary god of fire) is applied to those mountains which send forth from their summits or sides, flame, smoke, ashes, and streams of melted matter called lava. Upon ascending to the top of a mountain of this kind, there is found to be an immense and deep hollow, which is denominated the crater or cup. From most of the volcanoes which are not extinct, there is a smoke more or less frequently aising; but the eruptions, which are discharges of stones, ashes, lava, &c., accompanied with lofty columns of fire, violent explosions and concussions of the earth, happen at irregular and sometimes very long intervals. It seems to be a very general rule that the
What may be termed mud volcanoes, from their having eruptions of mud only, are another curious phenomenon. One of these, which is situated towards the middle of the island of Java, in a plain abounding with salt springs, is thus described in the 9th volume of the Batavian Transactions: "On approaching it from a distance, it is first discovered by a large volume of smoke, rising and disappearing at intervals of a few seconds, resembling the vapours arising from a violent surf: a dull noise is heard, like that of distant thunder. Having advanced so near, that the vision was no longer impeded by the smoke, a large hemispherical mass was observed, consisting of black earth mixed with water, about 16 feet in diameter, rising to the height of
Etna has been known to eject Water.
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
On Valleys and Plains. Valleys are the spaces lying between opposite ridges of mountains or of hills, bed of some torrent or river, which and their lowest part is commonly the originates in the higher grounds. Those between high mountains are in general clefts or fissures. narrow and long, resembling large In some of these
valleys, among the Alps and Pyrenees, it has been observed, that the nooks or 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.
Large islands exhibit, on a smaller scale, the same appearances as the continents: upon them, therefore, it is unnecessary to make any observations, but with respect to smaller islands, the circumstance of their commonly being in groups or chains, deserves attention. Some are banks of sand, just raised above the surface of the water. Many islands, especially those in the South Sea, owe their origin to the marine insects which produce the coral. Some groups, as has already been observed, appear to have been raised up by the action of submarine volcanoes. Since the bed of the ocean possesses as much variety of surface as the land, there is no doubt that groups or chains of islands very near to each other, and which have not been raised up by such processes as those just alluded to, are only the different summits of an extensive submarine system of mountains; and when these collections of islands lie
The plains of Quito are 12,000 feet above the level of the sea.
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 it 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 be tween 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 exclusive cause. The internal reservoirs by 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 Hydrostatics. It is also evident that 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,
This word, which is usually but incorrectly therefore, proceed from some vast body of water within the earth; and it has,
written Kobi or Cobi, signifies a naked desert.
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
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 suf ficiently 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.
level, the course of the stream becomes gradually slower, an effect which may be perceived, more or less, in all running waters that originate in mountainous or hilly tracts, and afterwards traverse the plains. The declivity of many great rivers is much less than might at first be supposed. The Maranon or Amazons has a descent of only 10 feet in 200 leagues of its course, that is, th part of an inch for every 1000 feet of that distance. The Loire, in France, between Pouilly and Briare, falls one foot in 7,500, but between Briare and Orleans, only one foot in 13,596. Even the rapid Rhine has not a descent of more than four feet in a mile, between Schaffhausen and Strasburg, and of two feet between the latter place and Schenckenschantz. When rivers proceed through mountainous and rugged country, they frequently fall over precipices and form cataracts, in some cases several hundred feet in depth. The most celebrated falls in the world are those of the Niagara, in North America.
In the tropical regions most of the rivers are subject to periodical overflowings of their banks, in consequence of the rains which annually fall in such abundance in those countries during the wet season. The overflow of the Nile was considered by the ancients, who were ignorant of its cause, as one of the greatest mysteries of nature, because in Egypt, where the overflow takes place, no rain ever falls. The apparent mystery is easily explained, by the circumstance of the rains descending upon the mountains in the interior of Africa where the Nile rises. The consequent accumulation of the waters among the high grounds gradually swells the river along its whole extent, and in about two months from the commencement of the rains, occasions those yearly inundations, without which, Egypt would be no better than a desert.
The disappearance of some rivers for a certain distance under ground is accounted for with equal facility. When a river is impeded in its course by a bank of solid rock, and finds beneath it a bed of a softer soil, the waters wear away the latter, and thus make for themselves a subterraneous passage. In this way are explained the sinking of the Rhone, between Seyssel, and l'Ecluse, and the formation, in Virginia, of the magnificent rock bridge which overhangs the course of the Cedar creek. In
Spain the phenomenon exhibited by the Guadiana, which has its waters dispersed in sandy and marshy grounds, whence they afterwards emerge in greater abundance, is to be referred to the absorbing power of the soil.
Rivers, in their junction with the sea, present several appearances worthy of notice. The opposition which takes place between the tide and their own currents occasions, in many instances, the collection at their mouths of banks of sand or mud, called bars, on account of the obstruction which they offer to navigation. Some streams rush with such force into the sea, that it is possible, for some distance, to distinguish their waters from those of the sea. The shock arising from the collision of the current of the majestic Amazons with the tide of the Atlantic is of the most tremendous description. Many of the largest rivers mingle with the sea by means of a single outlet, while others, for instance the Nile, the Ganges, the Volga, the Rhine, and the Orinoco, before their termination, divide into several branches*. This circumstance will depend upon the nature of the soil of the country through which a river runs; but it also frequently results from the velocity of the stream being so much diminished in its latter stage, that even a slight obstacle in the ground has power to change its course, and a number of channels are thus produced. Another cause may be assigned for the division into branches of those rivers, which, in tropical countries, periodically inundate the plains; the superfluous waters which, at those periods, spread over the country, find various outlets, which are afterwards rendered permanent by the deepening of the channels by each successive flood. In some of the sandy plains of the torrid zone the rivers divide into branches, and, from the nature of the soil and the heat of the climate, they are absorbed and evaporated, and thus never reach the sea.
Lakes tinct kinds. be classed into four dismay those which have no outlet, and which The first class includes do not receive any running water. They are usually very small; some appear to be the craters of extinct volcanoes filled
The triangular space formed by a river pouring itself into the sea by various mouths, is called a Delta, from its resemblance to the shape of the fourth letter (A) of the Greek alphabet,