PLUTONISTS.

SOME philosophers, perceiving the great difficulties under which the Neptunian system labours, have recourse to another agency in the formation of our world. They allow, indeed, the action of water in depositing strata at the bottom of the ocean; but they suppose them to have been consolidated, crystallized, and upraised by means of fire. This scheme seems to be the prevailing one of the present day; but it involves some very extravagant and contradictory opinions.

The first difficulty refers to the materials or "debris of a former world." What was the structure of that world, and how was it wrecked? Again, as to the central fire-when and where did it originate? How did it get to the earth's centre? How is it fed? Or, if mere heat, how has it been kept up for so long a time? Concerning these points, Plutonians are at issue amongst themselves; and we might very properly leave them alone until they shall have agreed upon the first principles of their theory. Mr. Playfair and his followers, down to Dr. Pye Smith, suppose that our globe was once intensely hot; that the surface has gradually cooled, and been formed into rocks; whilst the interior is still a mass of glowing liquid, by the unequal pressure upon which, frequent outbreaks or undulations take place, and volcanoes or earthquakes are consequently produced. But since this fire cannot be fed from any internal source, nor is there any visible inlet by which fuel is supplied, we should have thought that it would have become extinct long ago. To believe that there is a furnace of such immense size, thirty miles under our feet, whilst the ground is often frozen up with cold, and covered with snow, is in absolute contradiction to all the known usages of heat. This fire, moreover, is so amazingly fervid, as to have fused the lower strata, thereby destroying the organic remains which they are thought to have contained. But if the globe was once a ball of liquid fire, whence came the matter for fusing? "No," says Mr. Playfair, "the debris of a former world were left upon the surface, and the central heat has ascended as far as the lower strata and fused them, whilst it has not yet reached the outer layers." Then the fire must have been mounting upwards during the lapse of past ages, and, consequently, have been increasing instead of diminishing in intensity; which destroys the idea of an external cooling. And it is

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strange, that, when it got up so far, it did not contrive to ascend a little higher, and take possession of the whole planet.

Dr. Pye Smith, like other Plutonians, seriously informs us, that granite was amongst the last-formed rocks; yet, when speaking of gneiss, he says, "This is precisely that state which would be produced by an action upon the granitic surface, whether unaltered or somewhat disintegrated, of wearing off, removal, rolling about, diffusion in water, subsiding by its own weight, settlement at the bottom, and final disposition by the straight direction of a current." Strange, indeed! Gneiss is made out of disintegrated granite, yet granite is the most recent of all mineral substances! Gneiss is the most ancient of stratified rocks, lying at the bottom of regular strata, yet it originated from the debris of granite, which came last in the mineral formation! We should have thought that, in common consistency, the Huttonians would have fused the under strata of gneiss in order to compose the granite; but, in this case, they could not have accounted for the stratified rocks, without allowing a previous Neptunian deposition. Their theory involves a palpable contradiction.

Dr. Smith proceeds: "In a word, it is that state which those materials would necessarily acquire, in the way of being worn and arranged by water working upon them through a long space of time; also being farther acted upon by a heat transmitted from below." Is it really so? Has the Doctor ever picked up a piece of water-worn granite, and compared it with those beautiful specimens of shining gneiss which we have seen; and will he say, that the latter was composed out of the dull debris of the former? He tells us what "would necessarily " happen, with the same boldness of affirmation as if he had been present at the creation of a primitive rock; but we suspect that he knows nothing about the matter. Arguing upon his skill in manufacturing minerals, he proceeds to calculate the time necessary for making huge mountains of gneiss out of granitic remains! This process was effected by the agency of rivers and floods, which broke down the granular substances, and carried their particles into the bed of an ocean, where they were hot-pressed between the water above and fire below, being made very warm, yet not altogether melted like the more crystalline rocks! Nor need we wonder at their never becoming liquefied, when a cold ocean was poured over them: the marvel is, how they became sufficiently heated in so refrigerating a situation.

But who ever heard of perfect crystallization taking place without a solution of particles? Does fire crystallize stones? Does it not render them opaque and earthy. If Dr. Smith were able to melt gneiss in a flame, would he expect it to cool into granite?

Next in order are "the Cambrian and Cumbrian series; and their mode of formation is proved, by the most striking character, to have been the same as that of gneiss, modified by an increase and progressive composition of the materials." We acknowledge no such "proof," till it has been ascertained by experiment. We have seen some of the mountains which Dr. Smith describes; and we had no more idea of their being constructed out of gneiss, than we had of a human head being made out of an old neck and shoulders, because it is placed in the next higher region, and most of the materials are homogeneous. If geologists still inquire, "Whence came the gneiss and slate?" we ask, Whence came the skull and hair?

Again: there are large beds of crystalline rocks contained in the stratified. Primary limestone in the midst of mica-slate, quartzrock and conglomerates amongst clay-slate; there are distinct veins of granite pervading great mountains of the same mineral; there are porphyritic, serpentine, and trap veins perforating all the series; and soft minerals are found running through the hardest rocks. It is childish to account for such wonderful phenomena by supposing fissures to have been casually made, and the melted matter to have been poured in; for still the questions would arise: Whence came that matter? Who filtered it through? and how could such veins intersect one another so neatly? Or, who ever heard of volcanic fissures in a mountain, unaccompanied with great rents? These veins, however, seem as if they had been bored with an awl through the centre of the firmest beds. Besides, some of them run in such a direction as to be impracticable on the Huttonian hypothesis.

Having already found so many contradictions or impossibilities in this system, we would almost pass over another objection, though it also lies at the very root of the matter. We know that different substances require different solvent powers; and even those which are solved by the same agency undergo that solution at different degrees of temperature. But the Plutonian would fuse minerals, metals, and salts by the same fire; forgetting that a strong heat would decompose those crystals which water would dissolve; and, when once decomposed, how could

they be renewed? Are felspar, quartz, and mica all dissolvable by the same heat, so that one of them would not lose its pristine qualities before the others were fused? And would all admit of an easy re-composition? Or, supposing them to be only disintegrated by water, would mere hot-pressure amalgamate them into a hard rock like two pieces of metal joined by the blow-pipe? Would not such a fervid heat make the very ocean to boil? And what would become of metallic ores in such a furnace? Would they not have been fused into metals, and saved us the trouble of smelting?

In fact, the scheme will not bear even a slight investigation. Before Huttonians can hope to be credited in their marvellous speculations, they must exhibit a practical proof of their fancied mode of operation, at least on a small scale; by solving or decomposing a few minerals, and then precipitating, crystallizing, and agglutinating them by heat, according to their proper orders, and their several stratified appearances.

We shall quote some paragraphs from two published letters of Sir John Herschel, to show the pleasantry with which he treats the whole subject; (though Mr. Babbage seems to take it for serious truth;) only observing, that if philosophers may thus smile at each other's geological schemes, we may surely laugh at them all.

"Now for a bit of theory. Has it ever occurred to you to speculate upon the probable effect of the transfer of pressure? It has always been my greatest difficulty in Geology to find a primum mobile for the volcano, taken as a general, not a local, phenomenon. Davy's speculations about the oxidation of the alkaline metals seems to me a mere chemical dream. Poulet Scrope's notion of solid rocks flashing out into lava and vapour, on removal of pressure, and your statement of the probable cause of volcanic eruptions, appear to me wanting. The question stares us in the face, How came the gases to be so condensed? Why did they submit to be urged into liquefaction? If they were not originally elastic, but have become so by subterranean heat, whence came the heat? and why did it come? How came the pressure to be removed, or what caused the crack?" &c. &c. Sir John then proposes his own "speculation." "I would observe that a central heat may or may not exist for our purposes. And it seems to be a demonstrated fact, that temperature does, in all parts of the earth's surface yet examined, increase in going down towards the centre, in what I almost feel disposed to

call a frightfully rapid progression: and though that rapidity may cease, and the progression even take a contrary direction long before we reach the centre, (as it might do, for instance, had the earth, originally cold, been, as Poisson supposes, kept for a few billions or trillions of years, in a firmament full of burning suns, besetting every outlet of heat, and then launched on our cooler milky way,) still, as all we want is no more than a heat sufficient to melt silex, &c., I do not think we need trouble ourselves with any inquiries of the sort, but take it for granted, that a very moderate plunge downwards, in proportion to the earth's radius, will do all we want. Nay, the internal heat may be locally unequal; that is, great in Europe and Asia, small under America; as it would, for example, if, when roasting at Poisson's sun-fire, the great jack of the universe had stood still, and allowed one side of our terraqueous joint to scorch, and the other to remain underdone: a hint to those who are on the look-out for a cause (if any such there be) for the poles of maximum cold, and the general inferior temperature of the American climate, from end to end of that continent."

Had all geologists regarded their own and their neighbours' theories with the same good-humour as Sir John Herschel, we should have found no fault with their most extravagant fancies; for the wilder they had been, the more should we have been entertained with their perusal.

But since the doctrine of a central fire is repudiated by most of our natural philosophers, as being utterly inconsistent with the known laws of physics respecting heat, we shall leave our speculative Plutonians to settle this important point with the experimental school of Dr. Black, Professor Leslie, or Dr. Thomson.

NEBULARISTS.

WE should not have made any remarks upon the Nebular hypothesis, regarding it only as a playful fiction of Laplace, had not some late theorists been attempting to establish it in a serious Dr. Pye Smith informs us that it is gaining ground amongst geologists,-which certainly is no great inducement for us to put confidence in their logical powers. We shall therefore adduce it as an example of how very far a practical mineralogist

manner.