is dug up together with the coal, at Whitehaven, Newcastle, and other places, the people are employed to pick it out from among the coal, lest it should vitiate its quality, and render it less saleable. The pieces of the pyrites which are separated from the coal are not thrown aside as useless, but laid in heaps, for a purpose to be mentioned hereafter; and these heaps, not many years since, took fire both at Whitehaven and in the neighbourhood of Halifax. The same accident was observed above a hundred years ago at Puddle Wharf in London, where heaps of coal which contained much of this pyrites took' fire1. Though Lemery was the first person who, by artificial mixtures of sulphur and iron, produced fire, yet that natural mixtures of these substances would spontaneously take fire was known before he made his experiment. Thus, to omit what is said by Pliny" and the ancients, we are told by good authority, that one Wilson at Ealand in Yorkshire, about the year 1664 or before, had piled up in a barn many cartloads of the pyrites, or brass-lumps, as they were called by the colliers, for some secret purposes of his own: the roof of the barn happening to be bad, the pyrites were wetted by the rain; in this state they began to smoke, and presently took fire, and burned like red-hot coal. We have an account, in the Philosophical Transactions for 1693, of a covetous master of a copperas work at Whitestable in Kent, who, in order to break his neighbour's work, had engrossed all the pyrites or copperas-stone in the country: he built a shed over two or three hundred tons of these stones, to keep off the rain. In the space, however, of six or seven months, the mass (being probably wetted by the moisture of the atmosphere, or by the rain, which, notwithstanding the shed, might have fallen upon it) took fire and burned for a week; it quite destroyed his shed, and disappointed all his hopes of profit; for the pyrites was in part converted into a substance like melted metal, and in part it looked like red-hot stones: all the sulphur was consumed, and the neighbourhood was miserably afflicted by the noxious exhalation which it sent forth. In the month of August 1751, the cliffs near Charmouth in Dorsetshire took fire, in consequence of a heavy fall of rain after a hot and dry season, and they continued at intervals to emit flame for several years. These cliffs consist of a dark-coloured bituminous loam, in which are imbedded large quantities of different kinds of the pyrites. The same kind of flame has been frequently observed in the Cornish mines, and this mineral fire sometimes leads to the discovery of a mine; but wherever it is found to exist, the iron pyrites is ge.. nerally discovered near it1. 6 There are some sorts of earth from which alum is made, which abound so much with the pyrites, that the proprietors of the works are forced to keep them constantly well watered, in order to prevent their taking fire.-But it would be useless to pursue this subject further; we have adduced proof sufficient, that nature furnishes materials, which, under certain circumstances, may become the occasion of subterraneous fires. The requisite circumstances are a proper quantity of the materials, a proper portion of water to moisten them, and, perhaps, a communication with the air may be necessary. A small quantity of the pyrites is sufficient to kindle a fire; water is almost every where found in such great plenty below the surface of the earth, that it con · Philos. Trans. vol. lii. p. 119. stitutes one of the greatest impediments to our sinking pits to any great depth; and air, if it should be thought absolutely necessary to the spontaneous firing of the pyrites, may be conceived either to accompany the water in its dripping, or to descend into the innermost parts of the earth through the fissures which are found upon its surface. When a subterraneous fire is once kindled, it may be supported for ages by other substances, as well as by those which first gave rise to it: thus, if a quantity of the pyrites should take fire in a stratum of coal, or of shale, or of any other substance strongly impregnated with bitumen, the fire might continue till the stratum was consumed'. "There are such a great number of volcanos now subsisting in every quarter of the globe, and so many unequivocal vestiges of others, which in length of time have become extinct, that some philosophers think they have reason on their side in supposing, either that the earth, at some considerable distance below its surface, is surrounded with a stratum of ignited matter of a definite thickness; or that the whole central part of it is nothing but a mass of melted minerals, which every where struggling for vent, bursts forth where there is the least resistance, shivering into rude fragments the superincumbent crust of earth, and deluging with mountainous torrents of liquid fire the adjoining countries." This account of the origin of volcanos and subterraneous fires, as it is thus confirmed both by experiments and facts, will, I have no doubt, be very 1 There are some coaleries on fire now in Scotland, which were on fire in the time of Agricola.-Pennant's Tour in Scotland, part ii. p. 201. See an account of the coaleries on fire in Staffordshire, in Dr. Plott's Nat. Hist. of that county; and of the substances sublimed from the burning coalpits at Newcastle, in Philos. Trans. for 1676. satisfactory to my readers. In my next paper I shall offer some further observations, which appear to me of no small importance in the discussion of this curious and interesting subject. No. LV. FURTHER REFLECTIONS ON VOLCANOS; WITH A REFUTATION OF SOME OBJECTIONS DEDUCED FROM VOLCANIC PHENOMENA, AGAINST THE TRUTH OF REVELATION. The fluid lake that works below, Of herb, leaf, fruit and flower, from end to end MALLET. BESIDE the astonishing explosion of flames and smoke, of cinders and burning rocks, the eruptions of volcanos exhibit a dreadful phenomenon, in prodigious inundations of liquid fire, which bear inevitable destruction with them. The Italians give the name of lava to these fiery streams. This lava consists of a mixture of stones, sand, earth, metallic substances, salt, &c. calcined, rendered fusible, and vitrified, by the fire of the volcanos; but as the mass, of which it originally consists, is very heterogeneous, the lava, when cold, appears under various forms and colours. The purest sort is a hard, black, homogeneous compact glass. There is another species which is hard, heavy, and compact, like marble; susceptible of a very fine polish; and converted, at Naples, to a variety of domestic uses. There is another kind, which is a grosser stone, commonly ash-coloured, and used both for building, and for paving the streets. That which is found on the surface is still more gross and spongy, resembling the scoriæ, or recrements, of melted metals. It would carry me too far beyond the limits of this paper, if I were to enter into a historical account of the eruptions of volcanos. Those of Ætna and Vesuvius only would occupy many volumes. The violent eruption of Vesuvius, in 1767, is reckoned the 27th, since that which destroyed the cities of Herculaneum and Pompeii, in the reign of emperor Titus; and this eruption of 1767 has been succeeded by several others. Of the eruptions of Ætna, Mr. Oldenburg has given a historical account in the Philosophical Transactions, No. xlviii. p. 967. A very great eruption of this mountain was in the year 1669. The progress of the lava, or fiery deluge above described, was at the rate of a furlong a day. It advanced into the sea 600 yards, and was then a mile in breadth. It had destroyed, in forty days, the habitations of 27,000 persons; and of 20,000 inhabitants of the city of Catanea, only 3000 escaped. This inundation of liquid fire, in its progress, met with a lake four miles in compass, and not only filled it up, although it was four fathoms deep, but raised it into a mountain. Borelli, an ingenious Neapolitan, has calculated, that the |