TABLE OF GEOLOGICAL FORMATIONS,SHOWING THE FIRST APPEARANCE ON THE EARTH OF THE VARIOUS FORMS OF ANIMAL LIFE.
TABLE OF GEOLOGICAL FORMATIONS,SHOWING THE FIRST APPEARANCE ON THE EARTH OF THE VARIOUS FORMS OF ANIMAL LIFE.
This remarkable succession of animal life in the history of the Earth’s Crust will be more readily understood by means of the annexed Table. The remains of Invertebrate animals have been traced as far back as the Lower LaurentianRocks. The Vertebrate first become manifest in the Ludlow beds of the Upper Silurian; where they are represented by the bones of Fish, the lowest class belonging to the Province of Vertebrates. Next in order come the Reptiles: the oldest known Reptile having been found in the Coal Measures of Saarbrück between Strasburg and Treves. The skeletons of Birds are rare in the Stratified Rocks. It is supposed that their powers of flight have in all ages secured them, to great a extent, from being carried away by floods, like other land animals, and buried in the sedimentary deposits of rivers and estuaries. Nevertheless their presence in the ancient world is frequently attested by their footsteps, impressed originally on the sandy beach, and still preserved now that the soft sand has been converted into solid rock. Such traces have been discovered in great abundance on the New Red Sandstone of the Connecticut River in America; and afford the earliest evidence we possess in the records of Geology regarding the existence of the feathered tribe. This group of strata belongs to the lower Trias. In the higher beds of the same Formation we meet with the first relic of ancient Mammals. It was found near Stuttgardt, in 1847, and belongs to the more imperfect form of Mammalian life, the Non-Placental. Similar remains have been since discovered in the Upper Trias of Somersetshire. The Placental, or more perfect form of animal life in the same class, first appears in the Eocene Formation: and the bones of Man, the highest of the Placental, are found for the first time in the upper deposits of the Post-Tertiary Age.
Let it be remembered that we are here but stating the facts which have been hitherto brought to light by the researches of Geologists. It may be, it is indeed most probable, that new discoveries will lead to numerous modifications in our Table. There is no reason to suppose that Geologists have yet exhumed the earliest remains of Vertebratesor Invertebrates preserved in the Crust of the Earth: that Fish may not hereafter be traced back beyond the Silurian, or Reptiles beyond the Carboniferous Period: that Birds may not be found among the Primary Rocks, and Placentals among the Secondary. But in a science which depends mainly upon observation, it is better to register the facts we have than to speculate idly about those we have not. And, having registered them, we cannot fail to be struck with the succession of animal life on the Earth, to which they seem to point. It is certainly deserving of notice that, as far as the Organic Remains hitherto discovered may be taken as a guide, Invertebrates and Vertebrates, Fish, Reptiles, Birds, and Mammals, Non-Placentals and Placentals, follow one another in the ascending series of Geological Formations exactly in the same order as they follow one another in the ascending scale of Zoological Classification.
And so Geologists go on ever searching out new phenomena, and grouping them together into classes, until from particular facts they lead us to general truths. Then starting with these general truths as the groundwork of their science, they proceed to sketch out the Natural History of our Globe from the remotest ages of the past down to the present time. They first study the stratified deposits of each succeeding age, and analyze the Fossil Remains embedded therein; afterward they make their inferences, and they compile their history. They describe the forms, the character, the habits, of the plants and animals that flourished of old in this world of ours; they tell us where the deep sea rolled its waves in each succeeding age, and where the dry land appeared; they point out the Deltas of its ancient rivers, they measure the breadth of its Estuaries, they trace the course of its Glaciers, they mark the outlines of its Mountain chains. But with these and such like speculationswe are not here concerned. Many of them are open to controversy, and not a few are at this moment warmly disputed among Geologists themselves: besides, whether true or false, they do not in any way affect the relations between Geology and Revealed Religion. We shall be quite content, and it is all that our present scope demands, if we have made intelligible the general theory of Geological Chronology, and the kind of evidence on which it rests.
Before taking leave of this subject, however, we will venture to offer what seems to us an interesting illustration of the principles we have been explaining in the last two chapters;—one that will help to confirm the conclusions for which we have been contending, and that will also bring home to many minds the practical advantage to be derived from a thorough knowledge and just application of Geological science. Perhaps, too, it may help to revive the flagging attention of our readers; for the subject of our illustration isCoal, and the way to find it. In this age of manufactories and steam-engines,—when the atmosphere of great towns is heavy with smoke, and the quiet solitude of the country is so rudely disturbed by the shrieking of the railway-whistle and the snorting of the sooty locomotive,—this black, dirty mineral has acquired a value and importance, which may succeed in rousing even the practical money-making man to pay some heed to the lessons of science.
Coal might have been produced in any Geological Period; and in point of fact, beds of coal have been discovered in many different Formations. But in England, and in Western Europe generally, it has been found by long experience that the Coal-beds of the Carboniferous Formation are more abundant, and of better quality, than those of any other. Indeed the beds of Coal that occur in other Formations are so thin, and of such inferior quality, that they cannot be worked with profit. It is therefore of thehighest importance in the search for Coal, before going to the enormous expense of sinking deep shafts, to discover whether or no the rocks in which the search is to be made belong to the Carboniferous Period. In this matter the morepractical manis often seriously at fault. Coal-bearing strata generally consist pretty largely of dark-colored clay, black shales, and similar deposits. This is a fact which, as it strikes the eye, is perfectly familiar to all who are engaged in the working of Coal mines. Hence it happens, not unfrequently, that the practical man, when he meets with strata of this kind, is apt at once to infer that Coal is near at hand. The Geologist, on the contrary, knows well that such strata are not peculiar to the Carboniferous rocks, but are often found in other Formations in which there is no Coal at all, or at least no Coal that will repay the expense of working; and therefore he will pronounce it most rash to undertake costly works on the strength of these appearances. He has learned, however, that there are certain species of animals and plants which are found in the Carboniferous rocks and in them alone; he will search for these in the strata which it is proposed to explore, and by their presence or their absence he will know whether the strata in question belong to the Carboniferous Formation or not.
Again, it will often happen that, in the midst of an extensive region well known to abound in Coal, the rocks which appear at the surface in one particular locality, are not wholly devoid of Coal, but exhibit no resemblance either in mineral character or in Fossil Remains to the Coal-bearing strata. A question then arises of the highest practical importance. May it be that the Coal-bearing strata are spread out beneath this uppermost bed of rocks? and is it worth the expense to sink a shaft through the one in the hope of reaching the other? The practical miner has no very clear or certain principles to help him in the solutionof this problem; and thus it has often happened that thousands upon thousands of pounds have been expended in sinking shafts to look for Coal, where, as it afterward proved, there was not the slightest chance of finding it. Now, though Geology cannot tell if we shall succeed in finding Coal beneath these rocks, itcantell if there is agood chanceof succeeding. It can tell whether there is a reasonable hope, by penetrating into the Crust of the Earth at this particular spot, of reaching the Carboniferous Formation; and if we can reach the Carboniferous Formation in the midst of a Coal district, it is very likely we shall meet with beds of Coal.
His first object will be to ascertain what is the Formation to which the superficial rocks belong. If it be a Formation earlier in date than the Carboniferous,—the Silurian, for instance, or the Devonian,—he knows that it would be simply waste of money to look for Coal beneath them; because the Carboniferous rocks cannot possibly be found underneath the rocks of an earlier age. And so the Geologist can tell beforehand what the mere practical man would find out only when he had spent his money. If, on the other hand, the rocks which appear at the surface belong to a period later than the Carboniferous, the Geologist will not always conclude that it is expedient to sink a shaft in search of Coal. For though the Carboniferous rocks may, in this case, be underneath, they may be so far down in the Crust of the Earth that we should have no chance of ever reaching them. Suppose, for example, that the strata which appear at the surface belong to the Cretaceous Formation. He knows from his Chronological table that the Carboniferous age is separated from the Cretaceous by three intermediate Periods,—the Permian, the Triassic, the Jurassic. Therefore, when he finds the Cretaceous rocks at the surface in any locality, it is quite possible, though of course not certain, that before the Carboniferous Formationcould be reached it would be necessary to bore through thousands of feet of Jurassic, Triassic, and Permian rocks. And even then there would be no certainty of meeting with the Coal-bearing strata. Perhaps they were never deposited over this area of the earth’s surface; or, if deposited, perhaps they were subsequently swept away by Denudation. Hence our Geologist would reasonably conclude that, the probable expense of the search being so enormous, and the chance of success so remote, it would be much wiser not to make the attempt.
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.
I
Indeveloping 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, depositedunder 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 nowabove 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 stupendouschanges 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, thatthe 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,90which 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 temperaturecontinue 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 orfrom 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. Thebrushwood 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, whichcover nearly two-thirds of the area of our planet. Moreover, we have said nothing at all ofextinctVolcanos—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.
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.
H
Havingnow 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 enoughfor 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, toa 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, whichwere 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 abouttwo 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.”93Since 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 scrupulouscare. 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 townof 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 thewhole 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 togrow 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 feethigh, 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.”96By 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.