Consolations in Travel; or, the Last Days of a Philosopher

by Sir Humphry Davy

quantity of their larvæ may be seen there sometimes encrusted and entirely destroyed by calcareous matter, which is likewise often the fate of the insects themselves, as well as of various species of shell-fish that are found amongst the vegetables, which grow and are destroyed in the travertine on its banks. Snipes, ducks, and various water-birds, often visit those lakes, probably attracted by the temperature and the quantity of food in which they abound; but they usually confine themselves to the banks, as the carbonic acid disengaged from the surface would be fatal to them if they ventured to swim upon it when tranquil. In May, 18--, I fixed a stick on a mass of travertine covered by the water, and I examined it in the beginning of the April following for the purpose of determining the nature of the depositions. The water was lower at this time, yet I had some difficulty, by means of a sharp-pointed hammer, in breaking the mass which adhered to the bottom of the stick; it was several inches in thickness. The upper part was a mixture of light tufa and the leaves of confervæ; below this was a darker and more solid travertine, containing black and decomposed masses of confervæ; in the inferior part the travertine was more solid and of a grey colour, but with cavities which I have no doubt were produced by the decomposition of vegetable matter. I have passed many hours, I may say many days, in studying the phenomena of this wonderful lake; it has brought many trains of thought into my mind connected with the early changes of our globe, and I have sometimes reasoned from the forms of plants and animals preserved in marble in this warm source to the grander depositions in the secondary rocks, where the

zoophytes or coral insects have worked upon a grand scale, and where palms, and vegetables now unknown are preserved with the remains of crocodiles, turtles, and gigantic extinct animals of the sauri genus, and which appear to have belonged to a period when the whole globe possessed a much higher temperature. I have, likewise, often been led, from the remarkable phenomena surrounding me in that spot, to compare the works of man with those of Nature. The baths, erected there nearly twenty centuries ago, present only heaps of ruins, and even the bricks of which they were built, though hardened by fire, are crumbled into dust, whilst the masses of travertine around it, though formed by a variable source from the most perishable materials, have hardened by time, and the most perfect remains of the greatest ruins in the eternal city, such as the triumphal arches and the Colosæum, owe their duration to this source. Then, from all we know, this lake, except in some change in its dimensions, continues nearly in the same state in which it was described 1,700 years ago by Pliny, and I have no doubt contains the same kinds of floating islands, the same plants, and the same insects. During the fifteen years that I have known it it has appeared precisely identical in these respects, and yet it has the character of an accidental phenomenon depending upon subterraneous fire. How marvellous then are those laws by which even the humblest types of organic existence are preserved though born amidst the sources of their destruction, and by which a species of immortality is given to generations floating, as it were, like evanescent bubbles, on a stream raised from the deepest caverns of the earth, and instantly losing what may be

called its spirit in the atmosphere.” These last observations of the stranger recalled to my recollection some phenomena which I had observed many years ago, and of which I could then give no satisfactory explanation. I was shooting in the marshes which surround the ruins of Gabia, and where there are still remains supposed to be of the Alexandrine aqueduct; I observed a small insulated hill, apparently entirely composed of travertine, and from its summit there were formations of tufa which had evidently been produced by running water, but the whole mass was now perfectly dry and encrusted by vegetables. At first I suspected that this little mountain had been formed by a jet of calcareous water, a kind of small fountain analogous to the Geiser, which had deposited travertine and continued to rise through the basin flowing from a higher level; but the irregular form of the eminence did not correspond to this idea, and I remained perplexed with the fact and unable to satisfy myself as to its cause. The views of the stranger appeared to me now to make it probable that the calcareous water had issued from ancient leaks in the aqueduct and formed a hillock that had encased the bricks of the erection, which in other parts, where not encrusted by travertine, had become entirely decayed, degraded, and removed from the soil. I mentioned the circumstance and my suspicion of its nature. The stranger said: “You are perfectly correct in your idea. I know the spot well, and if you had not mentioned it I should probably have quoted it as an instance in which the works of art are preserved, as it were, by the accidents of Nature. I was so struck by this appearance last year that I had the travertine partially removed by

some workmen, and I found beneath it the canal of the aqueduct in a perfect state, and the bricks of the arches as uninjured as if freshly laid.” The stranger had hardly concluded this sentence when he was interrupted by Onuphrio, who said, “I have always supposed that in every geological system water is considered as the cause of the destruction or degradation of the surface, but in all the instances that you have mentioned it appears rather as a conservative power, not destroying but rather producing.” “It is the general vice of philosophical systems,” replied the stranger, “that they are usually founded upon a few facts, which they well explain, and are extended by the human fancy to all the phenomena of Nature, to many of which they must be contradictory. The human intellectual powers are so feeble that they can with difficulty embrace a single series of phenomena, and they consequently must fail when extended to the whole of Nature. Water by its common operation, as poured down from the atmosphere in rain and torrents, tends to level and degrade the surface, and carries the material of the land into the bosom of the ocean. Fire, on the contrary, in volcanic eruptions usually raises mountains, exalts the surface, and creates islands even in the midst of the sea. But these laws are not invariable, as the instances to which we have just referred prove, and parts of the surface of the globe are sometimes destroyed even by fire, of which examples may be seen in the Phlegræan fields, and islands raised by one volcanic eruption have been immerged in the sea by another. There are, in fact, no accidents in Nature; what we call accidents are the results of general laws in particular operation, but we cannot deduce these laws from

the particular operation or the general order from the partial result.” Ambrosio said to the stranger: “You appear, sir, to have paid so much attention to physical phenomena that few things would give us more pleasure than to know your opinion respecting the early changes and physical history of the globe, for I perceive you do not belong to the modern geological schools.” The stranger said, “I have certainly formed opinions or rather speculations on these subjects, but I fear they are hardly worth communicating; they have sometimes amused me in hours of idleness, but I doubt if they will amuse others.” I said, “The observations which you have already been so kind as to communicate to us, on the formation of the travertine, lead us not only to expect amusement but likewise instruction.”

The Stranger.—On these matters I had facts to communicate; on the geological scheme of the early history of the globe there are only analogies to guide us, which different minds may apply and interpret in different ways; but I will not trifle with a long preliminary discourse. Astronomical deductions and actual measures by triangulation prove that the globe is an oblate spheroid flattened at the poles, and this form we know, by strict mathematical demonstrations, is precisely the one which a fluid body revolving round its axis, and become solid at its surface by the slow dissipation of its heat or other causes, would assume. I suppose, therefore, that the globe, in the first state in which the imagination can venture to consider it, was a fluid mass with an immense atmosphere revolving in space round the sun, and that by its cooling a portion of its atmosphere was condensed in water which occupied a part of the surface. In this state no forms of life such as

now belong to our system could have inhabited it; and, I suppose, the crystalline rocks (or, as they are called by geologists, the primary rocks), which contain no vestiges of a former order of things, were the results of the first consolidation on its surface. Upon the further cooling the water which more or less had covered it contracted, depositions took place, shell-fish and coral insects of the first creation began their labours, and islands appeared in the midst of the ocean raised from the deep by the productive energies of millions of zoophytes. Those islands became covered with vegetables fitted to bear a high temperature, such as palms and various species of plants similar to those which now exist in the hottest parts of the world; and the submarine rocks or shores of these new formations of land became covered with aquatic vegetables, on which various species of shell-fish and common fishes found their nourishment. The fluids of the globe in cooling deposited a large quantity of the materials they held in solution, and these deposits agglutinating together the sand, the immense masses of coral rocks, and some of the remains of the shells and fishes found round the shores of the primitive lands, produced the first order of secondary rocks. As the temperature of the globe became lower, species of the oviparous reptiles were created to inhabit it; and the turtle, crocodile, and various gigantic animals of the sauri kind, seem to have haunted the bays and waters of the primitive lands. But in this state of things there was no order of events similar to the present; the crust of the globe was exceedingly slender, and the source of fire a small distance from the surface. In consequence of contraction in one part of the mass, cavities were opened, which

caused the entrance of water, and immense volcanic explosions took place, raising one part of the surface, depressing another, producing mountains, and causing new and extensive depositions from the primitive ocean. Changes of this kind must have been extremely frequent in the early epochas of nature, and the only living forms of which the remains are found in the strata that are the monuments of these changes, are those of plants, fishes, birds, and oviparous reptiles, which seem most fitted to exist in such a war of the elements. When these revolutions became less frequent, and the globe became still more cooled, and the inequalities of its temperature preserved by the mountain chains, more perfect animals became its inhabitants, many of which, such as the mammoth, megalonix, megatherium, and gigantic hyena, are now extinct. At this period the temperature of the ocean seems to have been not much higher than it is at present, and the changes produced by occasional eruptions of it have left no consolidated rocks. Yet one of these eruptions appears to have been of great extent and some duration, and seems to have been the cause of those immense quantities of water-worn stones, gravel and sand, which are usually called diluvian remains; and it is probable that this effect was connected with the elevation of a new continent in the southern hemisphere by volcanic fire. When the system of things became so permanent that the tremendous revolutions depending upon the destruction of the equilibrium between the heating and cooling agencies were no longer to be dreaded, the creation of man took place; and since that period there has been little alteration in the physical circumstances of our globe. Volcanoes sometimes occasion the rise of

new islands, portions of the old continent are constantly washed by rivers into the sea; but these changes are too insignificant to affect the destinies of man, or the nature of the physical circumstances of things. On the hypothesis that I have adopted, however, it must be remembered that the present surface of the globe is merely a thin crust surrounding a nucleus of fluid ignited matter, and consequently we can hardly be considered as actually safe from the danger of a catastrophe by fire.

Onuphrio said: “From the view you have taken, I conclude that you consider volcanic eruptions as owing to the central fire; indeed, their existence offers, I think, an argument for believing that the interior of the globe is fluid.” The stranger answered: “I beg you to consider the views I have been developing as merely hypothetical, one of the many resting places that may be taken by the imagination in considering this subject. There are, however, distinct facts in favour of the idea that the interior of the globe has a higher temperature than the surface; the heat increasing in mines the deeper we penetrate, and the number of warm sources which rise from great depths in almost all countries, are certainly favourable to the idea. The opinion that volcanoes are owing to this general and simple cause is, I think, likewise more agreeable to the analogies of things than to suppose them dependent upon partial chemical changes, such as the action of air and water upon the combustible bases of the earths and alkalies, though it is extremely probable that these substances may exist beneath the surface, and may occasion some results of volcanic fire; and on this subject my notion may, perhaps, be more trusted, as