by a very severe shock of an earthquake. The instantaneous and involuntary movement of each was to spring upon his feet, and I said, "This admits of no doubt." The words had scarce passed my lips, before we observed a large portion of the face of the cliff, about fifty yards on our left, falling, which it did with a violent crash. So soon as our first consternation had a little subsided, we removed about ten or a dozen yards further from the edge of the cliff, and finished our dinner.

On the succeeding day, June 15th, having the consul and some other friends on board, I weighed, and proceeded with the ship towards the volcano, with the intention of witnessing a night view; but in this expectation we were greatly disappointed, from the wind freshening and the weather becoming thick and hazy, and also from the volcano itself being clearly more quiescent than it was the preceding day. It seldom emitted any lightning, but occasionally as much flame as may be seen to issue from the top of a glasshouse or foundery chimney.

On passing directly under the great cloud of smoke, about three or four miles distant from the volcano, the decks of the ship were` covered with fine black ashes, which fell intermixt with small rain. We returned the next morning, and late on the evening of the same day I took my leave of St. Michael's to complete my cruize.

On opening the volcano clear of the NW part of the island, after dark on the 16th, we witnessed one or two eruptions that, had the ship been near enough, would have been awfully grand. It ap peared one continued blaze of lightning; but the distance which it was at from the ship, upwards of twenty miles, prevented our seeing it with effect.

Returning again towards St. Michael's on the 4th of July, I was obliged, by the state of the wind, to pass with the ship very close to the island, which was now completely formed by the volcano, being nearly the height of Matlock High Tor, about eighty yards above the sea. At this time it was perfectly tranquil; which circumstance determined me to land, and explore it more narrowly.

I left the ship in one of the boats, accompanied by some of the officers. As we approached, we perceived that was still smoking in many parts, and upon our reaching the island found the surf on the beach very high. Rowing round to the lee side, with some little

difficulty, by the aid of an oar, as a pole, I jumped on shore, and was followed by the other officers. We found a narrow beach of black ashes, from which the side of the island rose in general too steep to admit of our ascending; and where we could have clambered up, the mass of matter was much too hot to allow our proceeding more than a few yards in the ascent.

The declivity below the surface of the sea was equally steep, havings even fathoms water scarce the boat's length from the shore, and at the distance of twenty or thirty yards we sounded twenty-five fathoms.

From walking round it in about twelve minutes, I should judge that it was something less than a mile in circumference; but the most extraordinary part was the crater, the mouth of which, on the side facing St. Michael's, was nearly level with the sea. It was filled with water, at that time boiling, and was emptying itself into the sea by a small stream about six yards over, and by which I should suppose it was continually filled again at high water. This stream, close to the edge of the sea, was so hot, as only to admit the finger to be dipped suddenly in, and taken out again immediately.

It appeared evident, by the formation of this part of the island, that the sea had, during the eruptions, broke into the crater in two places, as the east side of the small stream was bounded by a precipice, a cliff between twenty and thirty feet high forming a peninsula of about the same dimensions in width, and from fifty to sixty feet long, connected with the other part of the island by a narrow ridge of cinders and lava, as an isthmus of from forty to fifty feet in length, from which the crater rose in the form of an amphitheatre.

This cliff, at two or three miles distance from the island, had the appearance of a work of art resembling a small fort or block-house, The top of this we were determined, if possible, to attain; but the difficulty we had to encounter in doing so was considerable; the only way to attempt it was up the side of the isthmus, which was so steep that the only mode by which we could effect it, was by fixing the end of an oar at the base, with the assistance of which we forced ourselves up in nearly a backward direction.

Having reached the summit of the isthmus, we found another difficulty, for it was impossible to walk upon it, as the descent on

the other side was immediate, and as steep as the one we had ascended; but by throwing our legs across it, as would be done on the ridge of a house, and moving ourselves forward by our hands, weat length reached that part of it where it gradually widened itself aud formed the summit of the cliff, which we found to have a perfectly flat surface, of the dimensions before stated.

Judging this to be the most conspicuous situation, we here planted the Union, and left a bottle sealed up containing a small account of the origin of the island, and of our having landed upon it, and naming it Sabrina Island.

Within the crater I found the complete skeleton of a guard fish, the bones of which being perfectly burnt, fell to pieces upon attempting to take them up; and by the account of the inhabitants on the coast of St. Michael's, great numbers of fish had been destroyed during the early part of the eruption, as large quantities, probably suffocated or poisoned, were occasionally found drifted into the small inlets or bays.

The island, like other volcanic productions, is composed princi pally of porous substances, and generally burnt to complete cinders, with occasional masses of a stone, which I should suppose to be a mixture of iron and lime-stone.

[Lowenorn. Payne's Geog. Extr. Phil. Trans. 1728. 1812.j

CHAP. XVII.

MINERALOGICAL REMARKS ON THE NATURE OF VOLCANIC MATERIALS.

THIS is a subject which still requires the attention of oryctologists. We are scarcely acquainted, says Dr. Thomson in his History of the Royal Society, with the nature of the rocks of which Etna or Vesuvius is composed: indeed, the task is extremely difficult; for these mountains are so surrounded with lava on all sides, that the rock itself, of which the mountain consisted before the volcano commenced, may perhaps be entirely concealed from view. The prodigious extent of

Etna, about a hundred miles in circumference, and the vast number of volcanic hills attached to its sides, at least forty-four in number, render the geognostic examination of the rocks, of which it was originally composed, almost impossible. Sir William Hamilton and several other writers on volcanoes suppose, that, previous to the commencement of the volcano, no mountain whatever existed; and that the whole mountain has been formed by successive eruptions from the crater. But this opinion is both improbable in itself, and destitute of evidence. Werner conceives, that volcanic hills are always composed of green stone, basalt, and the other rocks which constitute the independent coal formation, and the floetztrap. But the observations of Humboldt, on the volcanoes of America, will not admit of such conclusions; unless, indeed, we conceive granite and porphyry to belong to these formations; a supposition not very improbable, if we attend to the late observations of Von Buch and Professor Jameson; the former of whom in Norway, and the latter in Scotland, have found granite among secondary rocks.

Geologists are still deplorably ignorant of every thing relating to volcanic rocks. As a proof of this, it may be stated with truth, that the best treatise on volcanoes, which has hitherto appeared, was written by Bergmann, and published before the year 1780. Even lava itself, or the melted matter which issues from volcanoes, has been frequently confounded with basalt and green-stone. At one time it was the fashion to consider all hills composed of these two last rocks; and, in short, all filoetz-trap hills as extinct volcanoes. Thus, Fojas de St. Fond, in his travels through Scotland, finds every where abundance of extinct volcanoes; and Mr. Raspe inserted a paper in the Philosophical Transactions, describing similar hills in Hessia, under the same appellation. In like manner, the hills of Auvergne, in France, have been considered as extinct volcanoes by the French mineralogists; even D'Aubaisson, who was educated in an opposite school, has come to the same conclusion. Notwithstanding this, there can be little doubt that these hills stand in the same predicament with the floetz-trap hills of Scotland and Germany. These opinions, respecting the volcanic nature of basalt and green-stone, are now pretty generally laid aside. The followers of

* Phil. Trans. 1771. vol. lxi. p. 580.

Dr. Hutton, indeed, contend that they have been melted by heat, but do not suppose that they have ever belonged to a volcanic mountain.

Considerable doubts are entertained by some, whether pumice be a volcanic substance or not; and these doubts are founded on the supposition that pumice, though often observed in the neighbourhood of volcanoes, has never been seen mixed with lava, or actually flowing from a volcano. If the evidence of Tournefort be considered as sufficient, there can be no doubt that pumice is occasioually thrown out of volcanoes; for he describes various examples of it in his Voyage to the Levant. Pumice has been repeatedly observed floating on the surface of the sea, in immense quantity. To give one example, Mr. Dove, the captain of an Indiaman, observed it floating in the Atlantic Ocean, in immense abundance, over a tract of not less than 317 miles in length. The pumice was first observed in south latitude 35° 36′, west longitude 4° 9', and the shoals of it continued for several days*. Now it is impossible to account for such appearances on any other supposition than that the pumice has been thrown from the bottom of the sea by some volcanic force; and, if that be admitted, it will follow that pumice, at least some times, though perhaps not always, is volcanic.

The following observations of Spalanzani upon an accurate investigation of the Solfatara †, near Naples, are peculiarly entitled to the attention of the mineralogist.

* Phil. Trans. 1728. vol. xxxv. p. 444.

+ The lofty side of Solfatara, near Naples, seems to exhibit, in a miauter degree, whatever is seen of this horrible kind on the great theatre of nature. This plain, which is about twelve hundred feet long, and a thousand broad, is embosomed in mountains, and has in the middle of it a lake of noisome blackish water, covered with a bitumen that floats upon its surface. In every part of this plain, caverns appear smoking with sulphur, and often emitting flames. The earth, wherever we walk over it, trembles beneath the feet. Noises of flames, and the hissing of waters, are heard at the bottom. The water sometimes spouts up eight or ten feet high. The most noisome fumes, fœtid water, and sulphureous vapours, offend the smell. A stone thrown into any of the caverns, is ejected again with considerable violence. These appearances generally prevail when the sea is any ways disturbed; and the whole seems to exhibit marks of an earthquake in miniature,