Chapter XIV (1)

SUBTERRANEAN HEAT--ITS EXISTENCE DEMONSTRATED BY FACTS.

_Theory of stratified rocks supposes disturbances of the
earth’s crust--These disturbances ascribed by geologists
to the action of subterranean heat--The existence of
subterranean heat, and its power to move the crust of the
earth, proved by direct evidence--Supposed igneous origin of
our globe--Remarkable increase of temperature as we descend
into the earth’s crust--Hot springs--Artesian wells--Steam
issuing from crevices in the earth--The geysers of Iceland--A
glimpse at the subterranean fires--Mount Vesuvius in 1779--Vast
extent of volcanic action--Existence of subterranean heat an
established fact._

In developing the modern theory of Geology, we have all along assumed that the Crust of the Earth has been subject to frequent disturbances from the earliest ages of the world. Again and again, in the course of our argument, we have talked of the bed of the sea being lifted up, and converted into dry land; and, on the other hand, of the dry land being submerged beneath the waters of the sea. We have not even hesitated to suppose that these two opposite movements of upheaval and submersion often took place by turns over the same area; nay, that there is scarcely a region on the surface of the Globe which has not been several times submerged, and several times again upheaved.

Yet all this has not been taken for granted without proof. Our readers have seen what a long array of sober reasoning may be drawn out to show that the Stratified Rocks have been, for the most part, deposited _under water_:--first, from the nature and arrangement of the materials which compose them; secondly, from the character of the Organic Remains they contain. And since they are now _above water_, it is plain that either they have been lifted or the ocean has subsided. Furthermore, if we find, as we often do, two strata in immediate succession, the one underneath, exhibiting the trees of an ancient forest still standing erect with their roots attached, the other above, abounding in the remains of aquatic animals; we must conclude that when the ancient forest flourished this portion of the Earth’s Crust was above the level of the sea; that afterward it was submerged, and a new deposit, in which the marine remains were embedded, was spread out above the earlier vegetation; and that, last of all it again emerged from the waters, and became once more dry land. Finally, when a vertical section of the Earth’s Crust exhibits a continued series of such strata alternating with each other, it affords a proof that this particular area must have been several times under water, and several times again dry land, in the long course of ages.

These conclusions are now all but universally received among Geologists. The Crust of the Earth, we are assured, is not that unyielding and immovable mass which men commonly take it to be. On the contrary, it has been from the beginning ever restless and in motion, rising here and subsiding there, sometimes with a convulsive shock capable of upturning, twisting, distorting hard and stubborn rocks as if they were but flimsy layers of pliant clay; sometimes with a gentle, undulating movement, which, while it uplifts islands and continents, leaves the general aspect of the surface unchanged, the arrangement of the strata undisturbed, and even the most tender Fossils unharmed. Disturbances of this kind have been going on in various parts of the world even within the period of history; and they may be distinctly traced to the action of subterranean Heat. In support of a theory so startling and unexpected, Geologists appeal to the direct evidence of facts: and we now propose to bring some of these facts under the notice of our readers.

At the outset, however, it is important to set forth clearly the doctrine we hope to illustrate and confirm. With the origin of the internal heat that prevails within the Crust of the Earth we have no concern. This is still an unsettled point among Geologists themselves. Some conjecture that our Globe, when first launched into space, was in a state of igneous fusion; that is to say, that all the solid matter of which it is composed was held in a molten condition by the action of intense heat; that, in course of time, as this heat passed off by radiation, the surface gradually cooled and grew hard; that an external shell of solid rock was thus formed, which has been ever growing thicker in proportion as the Earth has been growing cooler; and that the actual condition of our planet is the result of this process continued down to the present day,--a fiery mass of seething mineral within, and a comparatively thin crust of consolidated rock without. Others suppose that the internal heat of the Globe is developed by the agency of chemical changes constantly going on in the depths of the Earth; and others, again, look for a cause to the action of electricity and magnetism. But these and such like speculations are still under discussion, and not one of them can be regarded as anything more, at best, than a satisfactory hypothesis. Anyhow, it is not about the causes of internal heat that we are just now interested, but about the fact of its existence, and the nature of its effects. Is it true that an intense heat prevails very generally beneath the superficial covering of the Globe? and is that heat capable of producing those stupendous changes which are ascribed to it in our theory of Geology? These are the questions to which we mean to devote our chief attention.

It is a very significant fact, that _the deeper we penetrate into the Crust of the Earth, the hotter it is_. At first, no doubt, for a short distance, the reverse is the case. When we begin to descend we find it cooler below than above, because the further we depart from the surface the more we are removed from the influence of the Sun. But at a certain point--in our climate at about fifty feet below the surface--the influence of the Sun’s heat ceases to be sensibly felt. When this limit is passed, the temperature begins to rise, and thenceforth the deeper we go the hotter the earth becomes.

This broad and general fact has been tested by experiments in every part of the world, and has been found true in all countries, in all climates, in all latitudes, whether in coal-pits, or mines, or deep subterranean caves. “In one and the same mine,” says Sir John Herschel,[89] “each particular depth has its own particular degree of heat, which never varies: but the lower always the hotter; and that not by a trifling, but what may well be called an astonishingly rapid rate of increase,--about a degree of the thermometer additional warmth for every ninety feet of additional depth,[90] which is about 58° per mile!--so that, if we had a shaft sunk a mile deep, we should find in the rock a heat of 105°, which is much hotter than the hottest summer day ever experienced in England.” Now if the temperature continue to increase at this rate toward the centre of the Earth, it is quite certain that, at no very great distance from the surface, the heat would be sufficiently intense to reduce the hardest granite and the most refractory metals to a state of igneous fusion.

Again, every one is familiar with the existence of hot springs, which come up from unknown depths in the Earth’s Crust, and which, appearing as they do in almost all parts of the world, testify in unmistakable language to the existence of internal heat. At Bath, for instance, in England, the water comes up from the bowels of the Earth, at a temperature of 117° Fahrenheit; and in the United States, on the Arkansas River, there is a spring at 180°--not much below the boiling point. This remarkable phenomenon, however, may be more closely investigated in the case of Artesian Wells, so called from the province of Artois, in France, where they first came into use. These wells are formed artificially, by boring down through the superficial strata of the Earth, sometimes to enormous depths, until water is reached. It has been found in every case that the water coming up from these great depths is always hot; and, furthermore, that the deeper the boring the hotter the water. A well of this kind was sunk in 1834 at Grenelle, in the suburbs of Paris, to a depth of more than 1800 English feet, and the water, which rushed up with surprising force, had a temperature of 82° Fahrenheit; whereas the mean temperature of the air in the cellars of the Paris Observatory is only 53°. The water has ever since continued to flow, and the temperature has never varied. At Salzwerth, in Germany, where the boring is still deeper, being 2,144 feet, the water which rises to the surface is 91° of our scale.

Then we have, in many countries, jets of steam which issue at a high temperature from crevices in the Earth, and which tell of the existence of heated water below, as plainly as the steam that escapes from the funnel of a locomotive or from the spout of a tea-kettle. Phenomena of this kind are very common in Italy, where they are sometimes exhibited at intervals along a line of country twenty miles in length. But in Iceland it is that they are displayed in the highest degree of splendor and power. On the southwest side of that island, within a circuit of two miles, there are nearly a hundred hot springs called Geysers, from some of which, at intervals, immense volumes of steam and boiling water are violently projected into the air. The Great Geyser is a natural tube, ten feet wide, descending into the Earth to a depth of seventy feet, and opening out above into a broad basin, from fifty to sixty feet in diameter. This basin, as well as the tube which connects it with the interior of the Earth, is lined with a beautifully smooth and hard plaster of siliceous cement, and is generally filled to the brim with water of a clear azure color, and a temperature little below boiling point. The ordinary condition of the spring is one of comparative repose, the water rising slowly in the tube and trickling over the edge of the stony basin. But every few hours an eruption takes place. Subterranean explosions are first heard, like the firing of distant cannon; then a violent ebullition follows, clouds of steam are given out, and jets of boiling water are cast up into the air. After a little the disturbance ceases, and all is quiet again. Once a day, or thereabouts, these phenomena are exhibited on a scale of extraordinary grandeur: the explosions which announce beforehand the approaching display are more numerous and violent than usual; then such volumes of steam rush forth as to obscure the atmosphere for half a mile around; and, finally, a vast column of water is projected to a height of from one to two hundred feet, and continues for a quarter of an hour to play like an artificial fountain. Geysers scarcely less grand and striking are to be seen in New Zealand, from which the water is thrown up at a temperature 214° Fahrenheit, or two degrees above boiling point.

Such are the evident symptoms of subterranean heat,--hot springs, jets of steam, fountains of boiling water,--which are manifested unceasingly at the surface of the Earth in every quarter of the Globe. But it is sometimes given us to behold, as it were, the subterranean fire itself, and to contemplate its power under a more striking and awful form. From time to time, in the fury of its rage, the fiery element bursts asunder the prison-house in which it is confined, and rushes forth into the light of day; then flames are seen to issue from the surface of the Earth, yawning chasms begin to appear on every side, the roaring of the furnaces is heard in the depths below, clouds of red-hot cinders are ejected high into the air, and streams of incandescent liquid rock are poured forth from every crevice, which, rolling far away through smiling fields and peaceful villages, carry destruction and desolation in their track. These are the ordinary phenomena of an active volcano during the period of eruption; and even while we write, most of them may be witnessed actually taking place for the hundredth time, on the historic ground of Mount Vesuvius. Our typical example, however, we shall take from the eruption of that mountain in the year 1779. It was not, indeed, especially remarkable for its violence or for the catastrophes by which it was attended; but it had the good fortune to be accurately recorded by an eye-witness, Sir William Hamilton, who, at that time, represented the English Government at the Court of Naples; and we are thus more minutely acquainted with all its various circumstances than with those of any other eruption of equal importance.

For two years before, the mountain had been in a state of excitement and disturbance. From time to time rumbling noises were heard underground, dense masses of smoke were emitted from the crater, liquid lava at a white heat bubbled up from crevices on the slopes of the mountain, and through these crevices a glimpse could be had here and there of the rocky caverns within, all “red-hot like a heated oven.” But in the month of August, 1779, the eruption reached its climax. About nine o’clock in the evening of Sunday the eighth, according to the graphic description of Sir William Hamilton, “there was a loud report, which shook the houses at Portici and its neighborhood to such a degree as to alarm the inhabitants and drive them out into the streets. Many windows were broken, and, as I have since seen, walls cracked, from the concussion of the air from that explosion. In one instant, a fountain of liquid transparent fire began to rise, and, gradually increasing, arrived at so amazing a height, as to strike every one who beheld it with the most awful astonishment. I shall scarcely be credited when I assure you that, to the best of my judgment, the height of this stupendous column of fire could not be less than three times that of Vesuvius itself, which, you know, rises perpendicularly near 3,700 feet above the level of the sea. Puffs of smoke, as black as can possibly be imagined, succeeded one another hastily, and accompanied the red-hot, transparent, and liquid lava, interrupting its splendid brightness here and there by patches of the darkest hue. Within these puffs of smoke, at the very moment of their emission from the crater, I could perceive a bright but pale electrical light playing about in zigzag lines. The liquid lava, mixed with scoriae and stones, after having mounted, I verily believe, at least 10,000 feet, falling perpendicularly on Vesuvius, covered its whole cone, and part of that of Somma, and the valley between them. The falling matter being nearly as vivid and inflamed as that which was continually issuing fresh from the crater, formed with it a complete body of fire, which could not be less than two miles and a half in breadth, and of the extraordinary height above mentioned, casting a heat to the distance of at least six miles around it. The brushwood of the mountain of Somma was soon in a flame, which, being of a different tint from the deep red of the matter thrown out from the Volcano, and from the silvery blue of the electrical fire, still added to the contrast of this most extraordinary scene. After the column of fire continued in full force for nearly half an hour the eruption ceased at once, and Vesuvius remained sullen and silent.”[91]

The existence, then, of intense heat within the Crust of the Earth may be regarded as an established fact where-ever an active Volcano appears at the surface. Now let us consider for a moment, the very extensive scale on which these fiery engines of Nature are distributed over the face of the Globe. First, on the great continent of America. The whole chain of the Andes--that stupendous ridge of mountains which stretches along the western coast of South America, from Tierra del Fuego on the south to the isthmus of Panama on the north--is studded over with Volcanos, most of which have been seen in active eruption within the last 300 years. Passing the narrow isthmus of Panama, this line of Volcanos may still be traced through Guatemala to Mexico, and thence northward even as far as the mouth of the Columbia River. Here is a vast volcanic region extending fully 6,000 miles in length, and spreading out its fiery arms, we know not how far, to the right and to the left. At Quito, just on the Equator, a branch shoots off toward the northeast, and, passing through New Granada and Venezuela, stretches away across the West India Islands, taking in St. Vincent, Dominica, Guadaloupe, and many others; while, in the opposite direction, it is certain that the volcanic action extends westward, far away beneath the waters of the Pacific, though we have no definite means of ascertaining where its influence ceases to be felt.

Another vast train of active Volcanos is that which skirts the eastern and southern coasts of Asia. Commencing on the shores of Northwestern America, it passes through the Aleutian Islands to Kamtschatka; then, in a sort of undulating curve, it winds its course by the Kurile Islands, the Japanese group, the Philippines, and the northeastern extremity of the Celebes, to the Moluccas. At this point it divides into two branches; one going in a southeasterly direction to New Guinea, the Solomon Islands, the Friendly Islands, and New Zealand; the other pursuing a northwesterly course through Java and Sumatra into the Bay of Bengal.

There is a third great line of volcanic fires which has been pretty well traced out by modern travellers, extending through China and Tartary to the Caucasus; thence over the countries bordering the Black Sea to the Grecian Archipelago; then on to Naples, Sicily, the Lipari Islands, the southern part of Spain and Portugal, and the Azores. Besides these there are numerous groups of Volcanos not apparently linked on to any regular volcanic chain, nor reduced as yet by scientific men to any general system; Mount Hecla, for instance, in Iceland, the Mountains of the Moon in Central Africa, Owhyhee in the Sandwich Islands, and many others rising up irregularly from the broad waters of the Pacific.

From this brief outline some idea may be formed of the magnificent scale on which volcanic agency is developed within the Crust of the Earth. It must be remembered, however, that any estimate based upon the enumeration we have given, would be, in all probability, far below the truth; for we have mentioned those Volcanos only which have attracted the notice of scientific men, or which have chanced to fall under the observation of travellers. Many others, doubtless, must exist in regions not yet explored, and in the profound depths of the seas and oceans, which cover nearly two-thirds of the area of our planet. Moreover, we have said nothing at all of _extinct_ Volcanos--such as those of Auvergne in France, and of the Rocky Mountains in America--which have not been in active operation within historical times; but in which, nevertheless, the hardened streams of lava, the volcanic ashes, and the cone-shaped mountains terminating in hollow craters, tell the story of eruptions in bygone ages, not less clearly than the blackened walls and charred timbers of some stately building bear witness to the passing wayfarer of a long extinguished conflagration.

We contend, therefore, that the doctrine of intense subterranean heat is not a wild conjecture, but is based on a solid groundwork of facts. First, there is presumptive evidence. In every deep mine, in every deep sinking of whatever kind, the heat of the earth increases rapidly as we descend. Hot water comes from great depths, and never cold. Sometimes it is boiling: sometimes it has been converted into steam. All this is found to be the case universally, whenever an opportunity has occurred for making the trial; and it seems to afford a strong presumption that if one could go still deeper, the heat would be found yet more intense, and would at length be capable of reducing to a liquid state the solid materials of which the earth is composed. Next, there is the direct testimony of our senses. A channel is opened from the depths below, flames are seen, red-hot cinders are cast up, and molten rock is poured out over the surface of the Earth in a liquid stream of fire. This evidence, however, though direct and conclusive as far as it goes, is not universal. It proves that an intense white heat prevails within the Crust of the Earth, not everywhere, but at least in those numerous and extensive regions where active Volcanos exist. So stands the case, as it seems to us, for the doctrine of subterranean heat as far as regards the fact of its existence.

_CHAPTER XV._

SUBTERRANEAN HEAT--ITS POWERS ILLUSTRATED BY VOLCANOS.

_Effects of subterranean heat in the present age of the
world--Vast accumulations of solid matter from the eruptions
of volcanos--Buried cities of Pompeii and Herculaneum--Curious
relics of Roman life--Monte Nuovo--Eruption of Jorullo in the
province of Mexico--Sumbawa in the Indian Archipelago--Volcanos
of Iceland--Mountain mass of Etna the product of volcanic
eruptions--Volcanic islands--In the Atlantic--In the
Mediterranean--Santorin in the Grecian Archipelago._

Having now sufficiently demonstrated the existence of intense subterranean heat, diffused, if not universally, at least very generally, beneath the superficial shell of the Earth, we shall next proceed to inquire if it is capable of effecting those physical changes which are ascribed to it in Geology;--of producing land where none before existed, of upheaving the solid Crust of the Earth, of driving the ocean from its bed, of dislocating and contorting solid masses of rock. The argument is still an appeal to facts. Such effects as these have been produced by the agency of internal heat, under actual observation, in the present age of the world; and it is not unreasonable to attribute to the same cause similar phenomena in ages gone by.

We will not run the risk of dissipating the force of this reasoning by attempting to expand it. It will be enough for us to state the facts: we shall leave it to our readers to estimate for themselves the value of the argument. There are three forms, more or less distinct, though closely associated, under which the subterranean fires have exerted their power in modern times to disturb and modify the Physical Geography of the Globe;--(1) the Volcano, (2) the Earthquake, (3) the gentle Undulation of the Earth’s Crust. Of these we shall speak in order.

In the case of Volcanos, as we have already sufficiently conveyed, the hidden furnaces of the Earth find a vent for their surplus energies; and when this vent is once established, that is to say, when the active Volcano has begun to exist, it seems probable that there is little further upheaval, properly so called, of the surface. Nevertheless, Volcanos contribute largely to the formation of land by the vast accumulation of ashes, mud, and lava, which they vomit forth. The destruction of Herculaneum and Pompeii is a case in point. For eight days successively, in the year 79, the ashes and pumice stone cast up from the crater of Vesuvius, fell down in one unceasing shower upon these devoted cities; while at the same time floods of water, carrying along the fine dust and light cinders, swept down the sides of the mountain in resistless torrents of mud, entering the houses, penetrating into every nook and crevice, and filling even the very wine jars in the underground cellars.

At the present moment the layers of volcanic matter beneath which Pompeii has been slumbering for centuries, are from twelve to fourteen feet over the tops of the houses. Loftier still is the pile that overlies the buried Herculaneum. This city, situated nearer to the base of the Volcano, has been exposed to the effects of many successive eruptions; and accordingly, spread out over the mass of ashes and pumice by which it was first overwhelmed, in the time of Pliny, we now find alternate layers of lava and volcanic mud, together with fresh accumulations of ashes, to a height, in many places, of 112 feet, and nowhere less than 70. Nor was this ejected matter confined to these two populous towns. It was scattered far and wide over the country around, and has contributed in no small degree to that extraordinary richness and fertility for which the soil of Naples is so justly famed.

As regards the production of land where none before existed, here is one fact of singular significance. At the time of the eruption, in 79, Pompeii was a seaport town to which merchantmen were wont to resort, and a flight of steps, which still remains, led down to the water’s edge: it is now more than a mile distant from the coast, and the tract of land which intervenes is composed entirely of volcanic tuff and ashes.

Gladly would we linger over the reminiscences of these luxurious and ill-fated cities. By the removal of the ashes, Pompeii is now laid open to view for at least one-third of its extent; and a strange sight it is, this ancient Roman city thus risen as it were from the grave,--risen, but yet lifeless,--with its silent streets, and its tenantless houses, and its empty Forum. Wherever we turn we have before us a curious and interesting picture, ghastly though it is, of the social, political, and domestic life of those ancient times, of the glory and the shame that hung around the last days of Pagan Rome;--in the theatres and the temples, in the shops and the private houses, in the graceful frescoes, in the elaborate mosaics, and, not least, in the idle scribblings on the walls, which, with a sort of whimsical reverence, have been spared by the destroying hand of Time. Then again, what a host of singular relics are there to be wondered at:--articles of domestic use and luxury, kitchen utensils and surgical instruments; female skeletons with the ornaments and vanities of the world, rings and bracelets and necklaces, still clinging to their charred remains; and strangest perhaps of all, eighty-four loaves of bread, which were put into the oven to bake 1800 years ago, and were taken out only yesterday, with the baker’s brand upon them, and the stamp of the baker’s elbow still freshly preserved in the centre of each. No subject could be more tempting to a writer, none more attractive to a reader. But our present purpose is to show the effects of Volcanos in elevating the level of the land; and so we must turn our back on the buried cities, and crossing the Bay of Naples, seek for a new illustration in the formation of Monte Nuovo, a lofty hill overlooking the ancient town of Pozzuoli.

About one o’clock at night, on Sunday, the twenty-ninth of September, 1538, flames were seen to issue from the ground close to the waters of the beautiful bay of Baiae. After a little, a sound like thunder was heard, the earth was rent asunder, and through the rent large stones, red-hot cinders, volcanic mud and volumes of water, were furiously vomited forth, which covered the whole country around, reaching even as far as Naples, and disfiguring its palaces and public buildings. The next morning it was found that a new mountain had been formed by the accumulation of ejected matter around the central opening. This mountain remains to the present day, and is called the Monte Nuovo. In form it is a regular volcanic cone, four hundred and forty feet high, and a mile and a half in circumference at its base, with an open crater in the centre, which descends nearly to the level of the sea. An eye-witness who has left us a minute account of this eruption, relates that on the third day he went up with many people to the top of the new hill, and looking down into the crater, saw the stones that had fallen to the bottom, “boiling up just as a caldron of water boils on the fire.” The same writer informs us--and it is very much to our present purpose to note the fact--that immediately before the eruption began, the relative position of land and sea was materially changed, the coast was sensibly upraised, the waters retired about two hundred paces, and multitudes of fish were raised high and dry upon the sand, a prey to the inhabitants of Pozzuoli.[92]

The Monte Nuovo is but a type of its class. If we travel westward 8,000 miles from Naples to the more stupendous Volcanos of the New World, we may witness the same phenomena on a still grander scale. In the province of Mexico, there is an elevated and extensive plain called Malpais, where for many generations the cotton plant, the indigo, and the sugar-cane, flourished luxuriantly in a soil richly endowed with natural gifts, and carefully cultivated by its industrious inhabitants. Everything was going on as usual in this smiling and prosperous region, and no one dreamed of danger, when suddenly, in the month of June, 1759, subterranean sounds were heard, attended with slight convulsions of the earth. These symptoms of internal commotion continued until the month of September, when they gradually died away, and tranquillity seemed to be restored. But it was only the delusive lull that precedes the fury of the storm. On the night of the twenty-eighth of September the rumbling sounds were heard again more violent than before. The inhabitants fled in consternation to a neighboring mountain, from the summit of which they looked back with wonder and dismay upon the utter annihilation of their homesteads and their farms. Flames broke out over an area half a square league in extent, the earth was burst open in many places, fragments of burning rock were thrown to prodigious heights in the air, torrents of boiling mud flowed over the plain, and thousands of little conical hills, called by the natives Hornitos or Ovens, rose up from the surface of the land. Finally a vast chasm was opened, and such quantities of ashes and fragmentary lava were ejected as to raise up six great mountain masses, which continued to increase during the five months that the eruption lasted. The least of these is 300 feet high, and the central one, now called Jorullo, which is still burning, is 1600 feet above the level of the plain. When Baron Humboldt visited this region just forty years after the eruption had ceased, the ground was still intensely hot, and “the Hornitos were pouring forth columns of steam twenty or thirty feet high, with a rumbling noise like that of a steam boiler.”[93] Since that time, however, the face of the country has become once more smiling and prosperous; the slopes of the newly-formed hills are now clothed with vegetation, and the sugar-cane and the indigo again flourish luxuriantly in the fertile plains below.

On the opposite side of the Globe, 10,000 miles from Mexico, we have had, almost in our own time, an exhibition of volcanic phenomena not less wonderful than those we have been describing. The island of Sumbawa lies about two hundred miles to the east of Java in the Indian Archipelago; and it belongs to that remarkable chain of Volcanos which we have already described as stretching, with little interruption, along the coast of Asia from Russian America to the Bay of Bengal. In the year 1815, this island was the scene of a calamitous eruption, the effects of which were felt over the whole of the Molucca Islands and Java, as well as over a considerable portion of Celebes, Sumatra, and Borneo. Indeed, so extraordinary are the incidents of this eruption, that we might well hesitate to believe them if they had not been collected on the spot with more than ordinary diligence, and recorded with an almost scrupulous care. Sir Stamford Raffles, who was at the time governor of Java, then a British possession, required all the residents in the various districts under his authority to send in a statement of the circumstances which occurred within their own knowledge; and from the accounts he received in this way, combined with other evidence, chiefly obtained from eye-witnesses, he drew up the narrative to which we are mainly indebted for the following facts.

The explosions which accompanied this eruption were heard in Sumatra, at a distance of 970 geographical miles; and in the opposite direction at Ternate, a distance of 720 miles. In the neighborhood of the Volcano itself, immense tracts of land were covered with burning lava, towns and villages were overwhelmed, all kinds of vegetation completely destroyed, and of 12,000 inhabitants in the province of Tomboro, only twenty-six survived. The ashes, which were ejected in great quantities, were carried like a vast cloud through the air, by the southeast monsoon, for 300 miles in the direction of Java; and, still farther to the west, we are told that they formed a floating mass in the ocean two feet thick and several miles in extent, through which ships with difficulty forced their way. It is recorded, too, that they fell so thick on the island of Tombock, 100 miles away, as to cover all the land two feet deep, destroying every particle of vegetation, insomuch that 44,000 people perished of the famine that ensued. “I have seen it computed,” writes Sir John Herschel, “that the quantity of ashes and lava vomited forth in this awful eruption would have formed three mountains the size of Mont Blanc, the highest of the Alps; and if spread over the surface of Germany, would have covered the whole of it two feet deep.” Finally, it appears that this eruption was accompanied, like that of Monte Nuovo, by a permanent change in the level of the adjoining coast; in this case, however, it was a movement, not of upheaval, but of subsidence: the town of Tomboro sunk beneath the ocean, which is now eighteen feet deep where there was dry land before.[94]

Once more we will ask our readers to take a rapid flight over the map of the world, passing, this time, from the Indian Archipelago to the island of Iceland,--that “wonderful land of frost and fire.” Besides the famous Volcano of Hecla, there are five others scarcely less formidable, all of which have been in active eruption within modern times. Of these the most celebrated is that of Skaptar Jokul. In the year 1783, this Volcano poured forth two streams of lava, which, when hardened, formed together one continuous layer of igneous rock, ninety miles in length, a hundred feet in height, and from seven to fifteen miles in breadth. The phenomena which accompanied the eruption are thus vividly described by Sir John Herschel:--“On the tenth of May innumerable fountains of fire were seen shooting up through the ice and snow which covered the mountain; and the principal river, called the Skapta, after rolling down a flood of foul and poisonous water, disappeared. Two days after, a torrent of lava poured down into the bed which the river had deserted. The river had run in a ravine 600 feet deep and 200 broad. This the lava entirely filled; and not only so, but it overflowed the surrounding country, and ran into a great lake, from which it instantly expelled the water in an explosion of steam. When the lake was fairly filled, the lava again overflowed and divided into two streams, one of which covered some ancient lava fields; the other re-entered the bed of the Skapta lower down, and presented the astounding sight of a cataract of liquid fire pouring over what was formerly the waterfall of Stapafoss. This was the greatest eruption on record in Europe. It lasted in its violence till the end of August, and closed with a violent earthquake; but for nearly the whole year a canopy of cinder-laden cloud hung over the island: the Faroe Islands, nay, even Shetland and the Orkneys, were deluged with ashes; and volcanic dust and a preternatural smoke which obscured the sun, covered all Europe as far as the Alps, over which it could not rise. The destruction of life in Iceland was frightful: 9,000 men, 11,000 cattle, 28,000 horses, and 190,000 sheep perished; mostly by suffocation. The lava ejected has been computed to amount in volume to more than twenty cubic miles.”[95]

With these very significant facts before us, it is hard to resist the conclusion that the great mountain mass of Etna, 11,000 feet high and ninety miles in circumference, is formed entirely of volcanic matter ejected during successive eruptions. For the whole mountain is nothing else than a series of concentric conical layers of ashes and lava, such as have been poured out more than once upon its existing surface in modern times. Just, then, as Monte Nuovo was produced by an outburst of volcanic power in a single night, and the far larger mountain of Jorullo in the course of a few months, so may we believe that the more stupendous Etna is the work of the same power operating through a period of many centuries. And applying this conclusion to many other mountains throughout the world of exactly the same structure, we come to form no very mean estimate of the permanent changes wrought on the physical geography of our Globe by the operations of volcanic agency.

We must remember, too, that volcanic eruptions are not confined to the land; they often break out in the bed of the sea. In such cases the waters are observed in a state of violent commotion, jets of steam and sulphurous vapor are emitted, light scoriaceous matter appears floating on the surface, and not unfrequently the volcanic cone itself slowly rises from the depths below, and continues to grow from day to day, until at length it becomes an island of no inconsiderable magnitude. Sometimes when the violence of the eruption has subsided, the new island, consisting chiefly of ashes and pumice-stone, is gradually washed away by the action of the waves; but in the other cases, these lighter substances are compacted together by the injection of liquid lava, and being thus able to withstand the erosive power of the ocean, assume the importance of permanent volcanic islands. Many examples of the former kind are recorded within the last hundred years. In 1783 an island was thrown up in the North Atlantic Ocean, about thirty miles to the southwest of Iceland. It was claimed by the King of Denmark, and called by him Nyöe or New Island; but before a year had elapsed, this portion of his Majesty’s dominion disappeared again beneath the waves, and the sea resumed its ancient domain. A cone-shaped island of the same kind, called Sabrina, three hundred feet high, with a crater in the centre, appeared amongst the Azores in 1811, but was quickly washed away again.

A more interesting example, because the circumstances are more minutely recorded, is the island which made its appearance in the Mediterranean, off the southwest coast of Sicily, in the year 1831. During its brief existence of three months, it received from contemporary writers seven different names; but the name of Graham Island seems to be the one by which it is most likely to be known to posterity. “About the tenth of July,” writes Sir Charles Lyell, “John Corrao, the captain of a Sicilian vessel, reported that, as he passed near the place, he saw a column of water like a waterspout, sixty feet high, and eight hundred yards in circumference, rising from the sea, and soon afterward a dense steam in its place, which ascended to the height of 1800 feet. The same Corrao, on his return from Girgenti, on the eighteenth of July, found a small island, twelve feet high, with a crater in the centre, ejecting volcanic matter and immense columns of vapor; the sea around being covered with floating cinders and dead fish. The scoriae were of a chocolate color, and the water, which boiled in the circular basin, was of a dingy red. The eruption continued with great violence to the end of the same month, at which time the island was visited by several persons, and amongst others by Captain Swinburne, R. N., and M. Hoffman, the Prussian Geologist.”[96] By the fourth of August the new island is said to have attained a height of 200 feet, and to have been three miles in circumference. Yet this was nothing more than the top of the volcanic cone; for, a few years before, Captain W. H. Smyth, in his survey, had found a depth of 600 feet at this very spot; and therefore the total height from the base of the mountain must have been 800 feet. From the beginning of August it began to melt away; and at the commencement of the following year, nothing remained of Graham Island but a dangerous shoal.

But even of the islands that occupy a prominent place on the map of the world, there is not wanting evidence to show that a large number derive their origin from the action of volcanic power. Among these may be mentioned many of the Molucca and Philippine groups, also several in the Grecian Archipelago, and not a few of the Azores and the Canaries,--in particular the lofty peak of Teneriffe, rising 12,000 feet above the level of the sea. In some cases, indeed, the actual process of their birth, and of their subsequent growth and development, has been minutely observed. A remarkable example occurs among the Aleutian Islands already referred to. In the year 1796 a column of smoke was seen to issue from the sea; then a small black point appeared at the surface of the water; then flames broke out, and other volcanic phenomena were exhibited; then the small black point grew into an island, and the island increased in size until it was at last several thousand feet high, and two or three miles in circumference. And such it remains to the present day.

_a._ Therasia.
_b._ The northern entrance, 1068 feet deep.
_c._ Thera.
_d._ Mount St. Elias, rising 1887 feet above the sea.
_e._ Aspronisi.
_f._ Little Kaimeni.
_g._ New Kaimeni.
_h._ Old Kaimeni.
_i._ Aphroessa.
_k._ George.]

The neighborhood of Santorin in the Grecian Archipelago has been noted from very remote times as the theatre of submarine eruptions. This island, which is itself to all appearance the crater of a vast volcano, has the form of a crescent, and, with the aid of two smaller islands which stretch across between the horns of the crescent, encloses an almost circular bay. We learn from Pliny that in the year 186 before Christ, within this bay an island rose up which was called Hiera or the Sacred island. It was twice enlarged during the Christian era, once in 726, and again in 1427, and still exists under the name of Palaia Kaimeni, that is to say, the Old Burnt Island. In 1573 a second island made its appearance, and received the name of the Little Burnt Island, Mikra Kaimeni. In 1707 and 1709, a third island was thrown up, and was distinguished from the other two as Nea Kaimeni, the New Burnt Island. Lastly, in 1866 the hidden volcanic power again became active, and two new vents were formed, called respectively Aphroessa and George. “At the end of January,” writes Sir Charles Lyell, “the sea had been observed in a state of ebullition off the southwest coast, and part of the Channel between New and Old Kaimeni, marked seventy fathoms in the Admiralty chart, had become, on February the eleventh, only twelve fathoms deep. According to M. Julius Schmidt, a gradual rising of the bottom went on until a small island made its appearance called afterward Aphroessa. It seems to have consisted of lava pressed upward and outward almost imperceptibly by steam, which was escaping at every pore through the hissing scoriaceous crust. ‘It could be seen,’ says Commander Lindesay Brine, R. N., ‘through the fissures in the cone that the rocks within were red hot, but it was not till later that an eruption began.’ On February the eleventh the village of Vulcano on the southeast coast, where there had been a partial sinking of the ground, was in great part overwhelmed by the materials cast out from a new vent which opened in that neighborhood, and to which the name of George was given, which finally, according to Schmidt, became about two hundred feet high.

“Commander Brine having ascended on February the twenty-eighth, 1866, to the top of the crater of Nea Kaimeni, about three hundred and fifty feet high, looked down upon the new vent then in full activity. The whole of the cone was swaying with an undulating motion to the right and left, and appeared sometimes to swell to nearly double its size and height, to throw out ridges like mountain spurs, till at last a broad chasm appeared across the top of the cone, accompanied by a tremendous roar of steam and the shooting up from the new crater, to the height of from fifty to a hundred feet, of tons of rock and ash mixed with smoke and steam. Some of these which fell on Mikra Kaimeni, at a distance of six hundred yards from the crater, measured thirty cubic feet. This effort over, the ridges slowly subsided, the cone lowered and closed in, and then, after a few minutes of comparative silence, the struggle would begin again with precisely similar sounds, action, and result. Threads of vapor escaping from the old crater of Nea Kaimeni proved that there was a subterranean connection between the new and the old vents. Aphroessa, of which the cone was at length raised to a height of more than sixty feet, was united in August with the main island. This was due in part at least to the upheaval of the bottom of the sea, which is now only seven fathoms deep in the channel dividing the New and Old Kaimenis, whereas in the Admiralty chart the soundings gave a hundred fathoms.”[97]

_CHAPTER XVI._

SUBTERRANEAN HEAT--ITS POWERS ILLUSTRATED BY EARTHQUAKES.

_Earthquakes and volcanos proceed from the same common
cause--Recent earthquakes in New Zealand--Vast tracts of
land permanently upraised--Earthquakes of Chili in the
present century--Crust of the Earth elevated--Earthquake of
Cutch in India, 1819--Remarkable instance of subsidence and
upheaval--Earthquake of Calabria, 1783--Earthquake of Lisbon,
1755--Great destruction of life and property--Earthquake
of Peru, August, 1868--General scene of ruin and
devastation--Great sea wave--A ship with all her crew carried a
quarter of a mile inland--Frequency of earthquakes._

The chief effect of volcanic eruptions on the Geological structure of our Globe consists in the accumulation of cinders and molten rock, either upon the Surface of the Earth, or in the crevices and caverns that abound within its solid Crust. Sometimes, indeed, the operations of an active Volcano are accompanied by a movement of upheaval or of subsidence. Thus for instance, we have seen that a portion of the Italian coast was elevated when Monte Nuovo was thrown up, that the town of Tomboro was submerged on the occasion of the eruption of Sumbawa, and that the bottom of the sea was notably upheaved by the last outbreak of the volcanic fires of Santorini. Nevertheless it appears to be generally the case that when the Crust of the Earth is once burst open, and a means of escape thus afforded to the fiery agent below,--in other words, when the active volcano is established,--the process of upheaval gives place to that of eruption. But when, as is often the case, no such safety-valve is offered to the surplus energies of the subterranean fires, then the giant power of heat, in its struggle to escape, shakes the foundation of the hills, and uplifts the superincumbent mass of solid rocks.

This theory which ascribes the phenomena of Earthquakes and Volcanos to the same common cause, acting under different circumstances, is now almost universally adopted by Geologists; and it may be briefly enforced by the following considerations. First, though Earthquakes have sometimes occurred far away from any known volcanic region, yet they are more frequent in the neighborhood of active or extinct Volcanos. Secondly, almost all volcanic eruptions are preceded by Earthquakes; and the Earthquakes generally cease, or, at least become less violent, when the subterranean fire breaks out in the form of a Volcano. And, Thirdly, it is plain that the condensed steam which is generated by internal heat, and the expansive power of the heat itself, must, of necessity, when pent up in the caverns of the Earth, tend to produce those very phenomena by which Earthquakes are distinguished.

Let it be observed, however, that while we explain the phenomena in question by the agency of subterranean heat, this doctrine is by no means necessary for the main purpose of our present argument. Whatever may be the cause from which the Earthquake shock proceeds, it is enough for us to show that the Crust of the Earth has been from time to time upraised, and dislocated, and rent asunder in modern times, just as it is supposed in Geological theory, to have been upraised, and dislocated, and rent asunder from time to time in by-gone ages. We will set down a few out of the many examples observed and recorded during the last hundred and twenty years.

When the English colonists settled in New Zealand, about fifty years ago, they were told by the natives that they might expect a great Earthquake every seven years. This alarming prediction has not been literally fulfilled; but it is fully admitted that the total number of such disturbances within the last half century has not fallen short of what it should have been according to the above estimate. During the years 1826 and 1827 several shocks were felt in the neighborhood of Cook Strait, after which it was observed that the sea-shore had been uplifted on the north side of Dusky Bay. So transformed was the outline of the coast that its former features could no longer be recognized; and a small cove called the Jail, which had previously afforded a commodious harbor to vessels, engaged in seal fishing, was completely dried up.

But the most memorable convulsion took place on the night of January the twenty-third, 1855. A tract of land, about as large as Yorkshire, on the southwest coast of the North Island, was permanently upraised from one to nine feet. The harbor of Port Nicholson, together with the valley of the Hutt, was elevated four to five feet; and a sunken rock, regarded before as dangerous to navigators, has remained since the Earthquake three feet above the level of the water. The shock was felt by ships at sea a hundred and fifty miles from the coast; and it is estimated that the whole area affected was not less than three times the extent of the British Islands.

The whole coast of Chili has been subject to great disturbances and changes of level during the present century. In November, 1837, the town of Valdivia was destroyed by an Earthquake, and at the same moment, a whaling vessel, a short distance out at sea, was violently shaken, and lost her masts. The bottom of the sea was afterward found to have been raised in some places more than eight feet; and several rocks appeared high above the water which had previously been covered at all times by the sea. Two years before, in 1835, the town of Conception and several others were reduced to ruins by a like visitation. After the first great convulsion the Earth remained for many days in a state of commotion. More than three hundred lesser shocks were counted from the twentieth of February to the fourth of March. On this occasion, too, the bed of the sea was upheaved; and the whole island of Santa Maria, seven miles in length, was lifted up from eight to ten feet above its former level.