having been more impregnated with sulphur at first than afterwards. The 29th, the mountain was very quiet, and the lava did not continue. The 30th, it began to flow again in the same direction, while the mouth of the volcano threw up every minute a girandole of red-hot stones, to an immense height. The 31st, he passed the night on the mountain: the lava was not so considerable as the first night, but the redhot stones were perfectly transparent, some of which, of a ton weight, mounted at least 200 feet perpendicular, and fell in, or near, the mouth of a little mountain, that was now formed by the quantity of ashes and stones, within the great mouth of the volcano, and which made the approach much safer than it had been for some days before, when the mouth was near half a mile in circumference, and the stones took every direction.

It is impossible to describe the beautiful appearance of these girandoles of red-hot stones, far surpassing the most astonishing artificial fire-work. On the 10th of April, at night, the lava disappeared on the side of the mountain towards Naples, and broke out with much more violence on the side next the Torre dell' Annunciata. It burst out of the side of the mountain, within about half a mile of the mouth of the volcano, like a torrent, attended with violent explosions, which threw up inflamed matter to a considerable height, the adjacent ground quivering like the timbers of a water-mill. Notwithstanding the consistency of the lava, it ran with amazing velocity; the first mile with a rapidity equal to that of the river Severn, at the passage near Bristol. The stream at its source was about 10 feet wide, but soon extended itself, and divided into three branches, so that these rivers of fire com municating their heat to the cinders of former lavas, between one branch and the other, had the appearance at night of a continued sheet of fire four miles in length, and in some parts near two in breadth. The glorious appearance of this uncommon scene is such as passes all description.

The lava, after having run pure for about 100 yards, began to collect cinders, stones, &c. and a scum was thus formed on its surface, which in the day-time had the appearance of the river Thames, after a hard frost and great fall of snow, when beginning to thaw, carrying down vast masses of snow and ice. In two places the liquid lava totally disappeared, and ran in a subterraneous passage for some paces, then came out again pure, having left the scum behind. In this manner it advanced to the cultivated parts of the mountain, destroying the cottages in its way. The lava, at the farthest extre

mity from its source, did not appear liquid, but like a heap of red-hot coals forming a wall, in some places 10 or 12 feet high, which rolling from the top soon formed another wall, and so on, advancing slowly, not more than about 30 feet in an hour.

The mouth of the volcano has not thrown up any large stones since the second eruption of lava, on the 10th of April, but has thrown up quantities of small ashes and pumice stones, that have greatly damaged the neighbouring vineyards. In his last visit to Mount Vesuvius the 3d of June, he still found that the lava continued, but the rivers were become rivulets, and had lost much of their rapidity.

Mount Etna in Sicily broke out on the 27th of April, and made a lava in two branches, at least six miles in length, and a mile in breadth, and that of Vesuvius resembled it in every respect, except that Mount Etna, at the place whence the lava flowed (which was 12 miles from the mouth of the volcano), threw up a fountain of liquid inflamed matter to a considerable height; which, he was told, Mount Vesuvius has done in former eruptions.

Formation of Islands. By ALEX. DALRYMPLE, Esq.-[1767.]

THERE is not a part of natural history more curious, or perhaps to a navigator more useful, than an enquiry into the formation of islands. The origin of islands in general is not the point to be discussed; but of low, flat islands in the wide ocean: such as are most of those hitherto discovered in the vast South Sea. These islands are generally long and narrow, they are formed by a narrow bar of land, inclosing the sea within it; generally, perhaps always, with some channel of ingress at least to the tide, commonly with an opening capable of receiving a canoe, and frequently sufficient to admit even larger vessels.

The origin of these islands will explain their nature. What led Mr. D. first to this deduction, was an observation of Abdul Roobin, a Sooloo pilot, that all the islands, lying off the N. E. coast of Borneo, had shoals to the eastward of them. These islands being covered to the westward by Borneo, the winds from that quarter do not attack them with violence.

The N. E. winds, tumbling in the billows from a wide ocean, heap up the coral with which those seas are filled. This, obvious after storms, is perhaps at all other times imperceptibly effected. Coral banks become dry. These

banks are found of all depths, at all distances from shore, entirely unconnected with the land, and detached from each other though it often happens that they are divided by a narrow gut, without bottom. Coral banks also grow, by a quick progression, towards the surface; but the winds, heaping up the coral from deeper water, chiefly accelerate the formation of these into shoals and islands. They become gradually shallower, and when once the sea meets with resistance, the coral is quickly thrown up by the force of the waves breaking against the bank; and hence it is that, in the open sea, there is scarcely an instance of a coral bank having so little water that a large ship cannot pass over, but it is also so shallow that a boat would ground on it. Mr. D. has seen these coral banks in all the stages; some in deep water, others with a few rocks appearing above the surface, some just formed into islands, without the least appearance of vegetation, and others, from such as have a few weeds on the highest part to those which are covered with large timber, with a bottomless sea at a pistol-shot distance.

The loose coral, rolled inward by the billows in large pieces, will ground, and the reflux being unable to carry them away, they become a bar to coagulate the sand, always found intermixed with coral; which sand, being easiest raised, will be lodged at top. When the sand bank is raised by violent storms, beyond the reach of common waves, it becomes a resting place to vagrant birds, whom the search of prey draws thither. The dung, feathers, &c. increase the soil, and prepare it for the reception of accidental roots, branches, and seed, cast up by the waves, or brought thither by birds. Thus islands are formed: the leaves and rotten branches, intermixing with the sand, form in time a light black mould, of which in general these islands consist, more sandy as less woody; and when full of large trees, with a greater proportion of mould. Cocoa nuts, continuing long in the sea without losing their vegetative powers, are commonly to be found in such islands; particularly as they are adapted to all soils, whether sandy, rich, or rocky.

The violence of the waves, within the tropics, must generally be directed to two points, according to the monsoons. Hence the islands formed from coral banks must be long and narrow, and lie nearly in a meridional direction. For even supposing the banks to be round, as they seldom are when large, the sea, meeting most resistance in the middle, must heave up the matter in greater quantities there than towards the extremities; and, by the same rule, the ends

will generally be open, or at least lowest. They will also commonly have soundings there, as the remains of the banks, not accumulated, will be under water. Where the coral banks are not exposed to the common monsoon, they will alter their direction; and be either round, or extend in the parallel, or be of irregular forms, according to accidental circumstances.

The interior parts of these islands, being sea, sometimes form harbours capable of receiving vessels of some burden, and he believes always abound greatly with fish; and such as he has seen, with turtle-grass and other sea-plants, particularly one species, called by the Sooloos gammye, which grows in little globules, and is somewhat pungent as well as acid to the taste. It need not be repeated, that the ends of those islands only are the places to expect soundings; and they commonly have a shallow spit running out from each point. Abdul Roobin's observation points out another circumstance, which may be useful to navigators; by consideration of the winds to which any islands are most exposed, to form a probable conjecture which side has deepest water; and from a view which side has the shoals, an idea may be formed which winds rage with most violence.

On the Eruption of Mount Vesuvius, in 1767. By the Hon. WILLIAM HAMILTON. Dated Naples, Dec. 29. 1767.

THE late violent eruption began October 19. 1767, and is reckoned to be the 27th since that which, in the time of Titus, destroyed Herculaneum and Pompeii. The eruption of 1766 continued in some degree till the 10th of December, about nine months in all, yet in that space of time the mountain did not cast up a third part so much as the quantity of lava which it disgorged in only seven days, the term of this last eruption.

The lava continued to run over the ancient crater in small streams, sometimes on one side, and sometimes on another, till the 18th of October, when there was not the least lava to be seen, owing, probably, to its being employed in forcing its way towards the place where it burst out the following day. Sir W. was surprised on the 19th following, at seven in the morning, to perceive every symptom of the eruption being just at hand. From the top of the little mountain issued a thick black smoke, so thick that it seemed to have difficulty in forcing its way out; cloud after cloud mounted with a hasty spiral motion, and every minute a volley of great stones were shot up to an immense height in the midst

of these clouds; by degrees, the smoke took the exact shape of a huge pine-tree, such as Pliny the younger described in his letter to Tacitus, where he gives an account of the fatal eruption in which his uncle perished. This column of black smoke, after having mounted an extraordinary height, bent with the wind towards Caprea, and actually reached over that island, which is not less than 28 miles from Vesuvius.

Before eight in the morning, the mountain had opened a mouth, without noise, about 100 yards lower than the ancient crater, on the side towards the Monte di Somma: as soon as it had vent, the smoke no longer came out with that violence from the top. On a sudden, about noon, Sir W. heard a violent noise within the mountain, which split; and, with much noise, from this new mouth a fountain of liquid fire shot up many feet high, and then like a torrent rolled on directly towards him. The earth shook, at the same time that a volley of pumice stones fell thick upon him; in an instant, clouds of black smoke and ashes caused almost a total darkness; the explosions from the top of the mountain were much louder than any thunder he ever heard, and the smell of the sulphur was very offensive. About two in the afternoon another stream of lava forced its way out of the same place as the lava came last year, so that the conflagration was soon as great on one side of the mountain as on the other.

The noise and smell of sulphur increasing, Sir W. removed from his villa to Naples; and he thought proper, as he passed by Portici, to inform the court of what he had seen; and humbly offered it as his opinion, that his Sicilian Majesty should leave the neighbourhood of the threatening mountain. However, the court did not leave Portici till about 12 o'clock. Sir W. observed, in his way to Naples, which was in less than two hours after he had left the mountain, that the lava had actually covered three miles of the very road through which he had retreated. It is astonishing that it should have run so fast; as he afterwards saw that the river of lava, in the Arrio di Cavallo, was 60 and 70 feet deep, and in some places near two miles broad. When his Sicilian Majesty quitted Portici, the noise was greatly increased, and the confusion of the air from the explosions was so violent, that, in the King's palace, doors and windows were forced open, and even one door there, which was locked, was burst open. At Naples, the same night, many windows and doors flew open. Besides the explosions, which were very frequent, there was a continued subterraneous and violent rumbling noise, which lasted this night about five hours. Sir W. imagined that this extra