"Mr. Watt having fused a large quantity of basalt, in the centre of the mass which was slowly cooled, the crystals of basalt were large; but they grew less as they approached the surface, which was amorphous and vitrified.

"The lava emitted from volcanoes is speedily decomposed by the action of moisture and the atmosphere, and forms the most fertile soils. No countries are more productive than those in the vicinity of volcanoes, if below the line of perpetual snow. The volcanic island of Santorin, which was raised in the Archipelago in one night, in the year 1770, is now in part covered with a luxuriant vegetation, and no country in Europe is more productive than the lower declivities of Etna.

"The operations of nature are on a scale too extended to be measured by days or years: they require ages to produce their full effect. What appears destructive and desolating at the first view, is found on a more comprehensive examination to be attended with permanent advantage. The lava and the ashes which burned Herculaneum and Pompeia, have furnished abundant harvests for fifteen centuries. The evils that nature inflicts are transient, but her benefits are of lasting duration."

It is unnecessary to warn the reader that this extract is not from the hand of the excellent author, and that of course it is only the general current of the ideas which deserves attention. But as the Germans have too much restricted, or rather annihilated, the influence of volcanoes, it seems here to be rather too much enlarged: for if we suppose two hundred existing volcanoes, and compute the medium of their agency at thirty miles each, the amount will be six thousand square miles, or at the most equal to the island of Sicily, about seven thousand two hundred. But the extinct volcanoes would probably more than double this extent; and it seems certain that in the chaotic and ancient state of the globe, before the component substances had acquired their present solidity and temperature, numerous volcanoes must have existed, which have been totally and radically extin

guished; while in modern times perhaps only two volcanoes wholly new have appeared, that of Jorullo, in New Spain, and that of Cahorra, under the peak of Teneriffe. The in

fluence of heat in the chaotic state of the world is well ex- Chaotic heat. plained by an able though anonymous author..

"Incessant and infinite motions must have existed in chaos, from the universal operation of endless varieties of unsaturated attractions and repulsions. In those vast fluctuations, therefore, of universally intermingled and heterogenous particles, quantities possessing every order and degree of affinity must have come within their mutual spheres of attraction. The weaker affinities must have been overpowered by the stronger; and thus, in the process of time, immense quantities of uniform quiescent and digested masses of matter must have been produced: and in these formations do we trace the first rudiments of organised nature. In them we find the origin of earths, metals, acids, alkalis, water, and atmospheric air.

"Combustion, or oxygenation, is the grand and principal chemical process by which most, if not all, such compounds are by the new system of chemistry known to be formed; even water itself, so long supposed to be a simple element, is now proved to be the combination of hydrogen and oxygen by combustion. Nature every where presents proofs of the agency of fire in her primary combinations!

"As fire has been seen to be the first process of nature in the formation of digested masses out of chaos, so is water found to be the great organ of arranging these masses in the next operation of nature, in the formation of the spheres: and here may I not for one moment pause, to observe how admirably this reconciles the contending opinions of geologists as to which of these agents has been employed by nature? Each of these sects has produced innumerable arguments, innumerable documents and instances, to prove his theory; and, in truth, nature abounds in appearances, in examples, of the agency both of fire and water. In the demonstrations before us we behold each serving in its turn the

great purposes of nature; we behold the one employed in the individual combination of substances, the other in the general arrangement of the whole. We behold the contradictory opinions of theory, and the diversity of appearances in nature, connected and harmonizing with the truths of modern chemistry!"

Nor must it be forgotten that our ideas of a chaotic state seem to be confined to this globe only, instead of being at least extended to our solar system. And if we conceive, with La Place, that the planetary bodies were formed by the concretion of an aëriform fluid, emanating from the sun, which derives its splendour from the Deity, the fountain of light, human imagination can never conceive the universal effervescence and developement of various vapours and gases, which must have appeared in the primeval universe. But in this and other grand ideas the prince of modern philosophers will ever be found to lead the way, having thus expressed himself in his immortal PRINCIPIA. "The vapours which arise from the sun, the fixed stars, and the tails of comets, may fall by their gravity into the atmospheres of the planets, where they may be condensed and converted into water and humid gases; and afterwards by a slow heat graduate into salts, and sulphurs, and tinctures, and mire, and mud, and clay, and sand, and stones, and corals, and other earthy substances."+ Did not this eagle of intuition thus foresee the pneumatic chemistry?

The important geological observations of Dr. Davy on the subject of volcanoes also excite, and may authorise, some other general remarks on the theory of the earth, which will not, it is hoped, be found wholly digressive.

Sketch of a New Demonstration of Nature, London 1810, 8vo.

+ Vapores autem qui ex sole, et stellis fixis, et caudis cometarum oriuntur, incidere possunt per gravitatem suam, in atmosphæras planetarum; et ibi con

densari, et converti in aquam et spiritus humidos: et subinde, per calorem lentum, in sales, et sulphura, et tincturas, et limum, et lutum, et argillam, et arenam, et lapides, et coralla, et substantias alias terrestres, paullatim migrare. NEWTON Princ. part ii. prop. 42.

The original violent rapidity of the earth's motion might cause a prodigious evaporation of the primeval waters, as in the tail of a comet: and in the general chaos of this solar system some esteem it not impossible that a satellite may have struck a planet, and have merged in it, or have been diffused over it; while the shock may have produced the refoulements of Saussure, which he seems to ascribe to an external cause *; in which he is followed by Dolomieu, who compares the strata of the globe to the shell of an egg, shattered by a squeeze of the hand. Some recent writers have also, on other grounds, adopted the same opinion.

As therefore, in the ideas of Newton and La Place, strengthened by many discoveries of pneumatic chemistry, the solar. fire must have been a prime agent in the creation, as it is still the chief agent of preservation, generation, and life, it may well be conceived, as nature always proportions the power to the effect, that the heat was at first violent, and gradually diminished to the present temperature. Hence the impressions of plants, which are now tropical, are found in climates at present temperate or frigid. The doctrine of central heat seems now to be universally abandoned, though if the nucleus of the earth consist of iron, according to the writers on magnetism, or of various metals which pass into earths, according to Dr. Davy, it is difficult to conceive that there should not be a certain heat peculiarly modified, as another modification exists in animal lifet. If we judge,

De Luc, though a Genevan, acknowledges that he does not understand Saussure's refoulement. Bertrand, another Genevan (Ren. Period. Paris an 8), interprets it subversion. Saussure himself distinguishes it from affaissement, and in one passage calls it un refoulement en sens contraire.

+ The nature and varieties of heat and light are far from being ascertained. Saussure, 2247, regards them as different substances, and observes that the point of the flame actuated by the blow-pipe, though not of a paler blue than the rest, yet, deprived of light, will convert gold into vapours, and yield the greatest heat excitable by art. But the appearance of light must depend on the degree of darkness, which no means seem to have been invented to increase.

Ferrara's theory.

however, from the external constitution, the predominant central substances are iron and silex, or the metal of silex. For silex itself, as already explained, is frequently a new production, found in the straw of graminous plants and the bark of the bamboo. Nay, pebbles of quartz are found in the bamboo itself; and often of the size of a pea in the eggs of the ostrich *.

Ferrara's able account of the volcanoes of Sicily has also opened some new geological ideas. In one passage he thus expresses himself: "The natural philosopher who has explained the formation, that is, the condensation and consolidation, of the globe, and the inequalities of its surface, as being produced by operations arising from an innate power in matter, from a power most generally diffused, from a power to which nature has put no limits of action upon the spot which we inhabit, but at the same time destined to bind all the parts of the universe together, in order to form a well-regulated whole; in a word, by gravitation: it would seem that he approaches nearer the verisimilitude of causes: he does not leave the earth in order to "explain the facts which are found in it; he has not created extraordinary powers; but has attributed all the phenomena to agencies which still operate, although upon another scale, but which would renew the same phenomena, if they were conducted under the same circumstances. From what I have said it may be understood that my opinion is with those who suppose that this globe was formed of materials which, being first diffused in a fluid, were thence deposited successively, and which occasioned all the disorder which we observe on the surface by the sinking of some parts, while others remain elevated in their original site and level. Burnet, who not long since started this grand and perhaps ancient idea, has

* See Barrow's Cape of Good Hope. Breislak, ii. 205, may be consulted for the dissolution of silex, which he says is effected by water impregnated with caloric, soda, and sulphur in a state of vapour. Kirwan, i. 155, says, oxyd of iron with microcosmic salt yields a pale green glass, that is, a siliceous substance.