Virgil, who seems, in my motto, to have copied this sublime description, has, in the five lines that follow it, introduced Enceladus in the same situation as Typhoeus.

From the consideration of Earthquakes in my last paper, the transition is natural to Volcanos, or burning mountains; especially as the hypothesis, that earthquakes are caused by subterraneous fires, has still so many advocates, and is maintained, in particular, by Mr. Whitehurst, the last ingenious naturalist who has written upon this subject.-This philosopher apprehends that subterraneous fire must, at different times, have existed universally in the bowels of the earth, and that in union with water, or by the expansive power of steam, it has produced the immense continents, as well as the mountains of our globe, and also the universal deluge1.

Dr. Watson, bishop of Landaff, has some admirable reflections on this subject in his Chemical Essays. "The most remarkable changes (says he) which have taken place in the form and constitution of the earth, since the deluge, have probably been produced by subterraneous fires; for it is to their agency that philosophers ascribe volcanos and earthquakes; those tremendous instruments of nature, by which she converts plains into mountains, the ocean into islands, and dry land into stagnant pools.

'Dr. Hooke formerly had maintained, that all land had been raised out of the sea by earthquakes; and modern philosophers seem to admit his hypothesis, though not, perhaps, in its utmost latitude. Thus one of them is of opinion, that Iceland, which is bigger than Ireland, has been produced by volcanos in the course of several centuries. Another, after

Inquiry into the Original State and Formation of the Earth.

2 Letters on Iceland by Dr. Uno Von Troil, p. 222.

giving an ingenious conjecture concerning the origin of all the tropical low isles in the South Sea, assures us, that of the higher isles there is hardly one of them which has not strong vestiges of its having undergone some violent alteration by a volcano. Some of them have volcanos still subsisting; others, among which are Otaheite and Huaheine, seem to have been elevated, in remote ages, from the bottom of the sea by subterraneous fires'.

"When these fires were first kindled; by what sort of fuel they are still maintained; at what depths below the surface of the earth they are placed; whether they have a mutual communication; of what dimensions they consist; and how long they may continue, are questions which do not admit an easy decision. The surface of the earth is admirably fitted for the support of the existence and well-being of all the animals which inhabit it. God has given us the ability also to penetrate a very little below this surface; and as the reward of our industry, he has placed within our reach a great variety of useful minerals; but as to the central recesses of the globe, we can never penetrate into them. A gnat essaying the feeble efforts of its slender proboscis against the hide of an elephant, and attempting thereby to investigate the internal formation of the body of that huge animal, is no unapt representation of man attempting to explore the internal structure of the earth by digging little holes upon its surface.

'But though it will ever be impossible for us to search far into the bowels of the earth, or to imitate in an extensive degree, the great operations which are constantly carrying on beneath its surface, yet it affords a curious mind no mean degree of satisfac

1 Observations made during a Voyage round the World by Dr. Forster, p. 151.

tion to be able, by obvious experiments, to form some reasonable conjectures concerning them.

'Mr. Lemery', as far as I have been able to learn, was the first person who illustrated, by actual experiment, the origin of subterraneous fires. He mixed twenty-five pounds of powdered sulphur with an equal weight of iron filings; and having kneaded the mixture together, by means of a little water, into the consistence of a paste, he put it into an iron pot, covered it with a cloth, and buried the whole a foot under ground. In about eight or nine hours time the earth swelled, grew warm, and cracked: hot sulphureous vapours were perceived; a flame which dilated the cracks was observed; the superincumbent earth was covered with a yellow and black powder: in short, a subterraneous fire, producing a volcano in miniature, was spontaneously lighted up from the reciprocal actions of sulphur, iron, and water.

That part of this experiment which relates to the production of fire, by the fermentation of iron filings and sulphur when made into a paste, has been frequently repeated since the time of Mr. Lemery. I myself have made it more than once, but I have nothing material to add to his account, except that the flame, when the experiment is made in the open air, is of very short duration; and the whole mass, after the extinction of the flame, continues at intervals, for a longer or shorter time, according to its quantity, to throw out sparks; and that a ladle full of the ignited mass, being dropped down from a considerable height, descends like a shower of red-hot ashes, much resembling the paintings of the eruptions of Mount Vesuvius, which may be seen at the British Museum. It has been observed, that large quantities of the materials are not requisite to make

'Cours de Chimie, p. 176.

pro

the experiment succeed, provided there be a due portion of water: half a pound of steel filings, half a pound of flower of brimstone, and fourteen ounces of water will, when well mixed, acquire heat enough to make the mass take fire.

"That heat and fire should be generated from the spontaneous actions of minerals upon each other, is a phenomenon by no means singular in nature, how difficult soever it may be to account for it. The heat of putrescent dunghills, of the fermenting juices of vegetables, and, above all, the spontaneous firing of hay not properly dried, are obvious proofs that vegetables possess this property as well as minerals. In both vegetables and minerals, a definite quantity of moisture is requisite to enable them to commence that intestine motion of their parts, which is necessary for the production of fire. Iron and sulphur would remain mixed together for ages without taking fire, if they were either kept perfectly free from moisture, or drenched with too much water; and vegetables in like manner, which are quite dry, or exceedingly wet, are incapable of taking fire while they continue in that state1.

But though it is certain from the experiment, that mixtures of iron and sulphur, when moistened with a proper quantity of water, will spontaneously take fire; yet the origin of subterraneous fires cannot, with any degree of probability, be referred to the same principle, unless it can be shown that nature has combined together in large quantities iron and sulphur, and distributed the composition through various internal parts of the earth.

Now that this is really the case we can have no doubt. There is, perhaps, no mineral more commonly met with than that which is composed of iron

1 Animal substances, when laid on heaps, have been observed to take fire.

and sulphur. It is found not only upon the face of the earth, but at the greatest depths below it, to which mines have been hitherto driven; not only in England or Italy, Europe or Asia, but in all parts of the world. This mineral is called in some parts of England, copperas-stone; in others, brazil; in others, brass-lumps; in others, rust-balls; in others, horse-gold; in others, marcasite; though naturalists are now, I think, agreed to give that name to such mineral bodies as are angular and crystallized, especially into a cubical form. The scientific name is pyrites, fiery: a denomination expressive enough of the property which this mineral has of striking fire with steel, and of spontaneously taking fire, when laid in heaps, and moistened with water.

6

Sulphur and iron are the chief constituent parts of the pyrites; arsenic, however, is sometimes united with the iron instead of sulphur, and sometimes sulphur and arsenic are both of them combined with iron. The pyrites also, accidentally, contains copper, silver, and perhaps gold: hence the pyrites has been distinguished by mineralogists into various sorts, by attending, either to its internal constitution, as the iron, the copper, the sulphureous, the arsenical pyrites; or to its external figure, as the pyramidal, the cubical, the spherical, the prismatic pyrites; or to its colour, as the gray, white, yellowish, yellow, orange pyrites.

6

Though the reader may have never contemplated the various species of the pyrites in any cabinet of natural history, or taken notice of such kinds as are commonly to be met with in chalk-pits, in beds of clay, or upon the seashore in many places of England, yet the yellowish matter, often adhering to, or mixed with the substance of pit-coal, cannot, surely, have escaped his observation: that matter consists of sulphur and iron, and is a species of the pyrites. So much of this sort of the pyrites