standing all the researches that have recently been made on volcanos, there is nothing but the study of volcanic products, which has made any progress. As to the nature of the combustibles which nourish those subterranean fires, we are very far from being able to give an explication, which, without being contrary to the rules of chemistry and of physics can account for the great phenomena, which volcanic explosions present.' But it is time to see what new light our author has elicited from the hitherto neglected Azores. These islands are represented as exhibiting at every step marks of a comparatively recent formation. St Michael, the one which he examined, is bounded by high precipitous shores, and broken by a range of hills and mountains running through it nearly in an east and west direction. These mountains are not in one continuous chain, but are for the most part completely separated at their bases, having the usual volcanic conical form, the summits being sometimes sharply acuminated, and sometimes truncated and hollowed into basins, some of which are several miles in circuit, and filled with water so as to form considerable lakes. The vallies and level lands of the island are all of the same volcanic character, the surfaces, as deep as could be examined, being either lava unchanged or decomposed, and converted into breccia, or beds of pumice, or tuff, or scoriæ, in a word some one of the various substances ejected from the craters. We know not, therefore, upon what this volcanic mass rests; it gives us no other insight into its history, than what its products afford. Among these there are very few, if any, which distinguish it from the volcanos before known, but it presents us with nearly all the substances, which have been collected from the others, as well those which are still in activity as those which have been long extinguished.

Of lithoid lavas we have the several varieties produced by their two chief constituents, felspar and augite, according to the proportions in which they are found, and the greater or less abundance of their usual accessories, hornblende and oxidulous iron. The porphyritic lava, or trachyte, is the most abundant; basalt, the other principal volcanic rock, occurs but rarely. The lavas which have lost their lithoid character, and become vitrified or scorious, are seen in great quantities. The obsidian, which is for the most part trachytic, is described as less compact than that of Iceland, but quite as beautiful in colour and lustre. It is found in the ravines among the loose

rocks, sometimes imbedded in the masses of pumice, which in many parts of the island cover a great extent of surface. These two volcanic products are observed constantly passing from one into the other, leaving it scarcely possible to distinguish the line of separation, still less to doubt that they were at one time the same identical substance. All the other marks by which the mighty effects of the agency of fire are recognized, such as scoriæ, volcanic sand, ashes, tuff, breccias, and lava in every state of decomposition and new combination, are spread over the whole island, so as to leave no doubt which of the elements has exercised dominion there. A farther resemblance to the volcanos heretofore known is observed in the minerals found by Dr Webster among the rocks of St Michael, which had undergone either but a slight or no change by the action of fire. Those mentioned by him are felspar, augite, hornblende, olivine, mica, haüyne, leucite, arragonite, and oxidulous iron, but he does not appear to have found either meionite, nepheline, or pleonaste, which are thus far the peculiar characteristics of Vesuvius. In many respects, however, the masses, which contain these minerals from St Michael, have a striking resemblance to those from Vesuvius, particularly a semivitrified kind of felspar, which we doubt not is the eisspath of Werner and the German mineralogists. We trace also an almost perfect similarity to the solfatara of the Campi Phlegræi, in his description of the country around the Caldeiras:

'As we pass along the narrow road from the village to this spot,' says our author, the gradual change from a fertile to a barren soil is observed, and within a few yards of the hot springs, nearly all traces of vegetation are lost. At the extremity of the road, the ground is almost snow white, and then acquires a reddish tinge; this increases in intensity and brightness, and finally passes through an infinite variety of shades to a deep brown. The vicinity of the springs is indicated by the increased temperature of the earth, a sulphureous odour, and the escape of vapour or steam from every crack and fissure in the ground. The volumes of smoke and steam rolling upwards from the surface to a great height, till they are gradually diffused through the atmosphere, or mingle with the heavier clouds that crown the summit of the mountains, produce a striking effect.

A few yards from the principal Caldeira is an elevation of about fifty feet in height, and probably as many in extent, composed of alternate layers of a coarser variety of sinter and clay, including grass, ferns, and reeds in different states of petrifac

tion. Not many years since, the side of this hill fell in, and discovered a deep and frightful chasm; smoke and steam at present issue from it in vast quantities, accompanied by a tremendous noise. Looking down through this opening, a body of water is seen boiling with great violence. An appalling roar is incessantly reverberated from side to side within the dome, and is increased at short intervals by sudden and violent explosions. The surface of this hill, the sides of the cavern, and the innumerable crevices in the ground are coated with sulphur. Every stone has been more or less changed, while not a shrub or plant flourishes for many yards around.'

There is not a little in this description to remind one of the 'Locus exciso penitus demersus hiatu

Parthenopen inter magnæque Dicarchidos arva
Cocyta perfusus aqua,'

of Petronius.

Dr Webster suspected that sulphuret of iron in the act of decomposition was the cause of the phenomena observed about these hot springs, and on digging, he had the satisfaction of finding large quantities, several feet below the surface, under loose masses of basaltic fragments, which contained, without doubt, microscopic portions of the sulphuret. Breislak found the same at Solfatara, and regards its operations in the same light. There is nothing unreasonable in supposing it to be the cause of such partial and confined effects, but we do not see how it could ever have been thought adequate to the production and enkindling of volcanic fires.

It would be thought unreasonable perhaps to complain of our author for not doing more, when he has done so much, and been so faithful in what he has done, but we should have been pleased if he had furnished us with a few more means of judging of the antiquity of these volcanos, and of the number. of eruptions they have poured out. The depth of the currents of lava might in many cases be exactly ascertained, and the fact determined whether they flowed over others more ancient, or whether the whole surface of the island above water is the effect of one mighty convulsion. We are inclined to believe, from all that we gather from his accounts, that it is the production of repeated volcanic eruptions, but that none of them ever burned for any considerable time. It is not improbable even that a process has been employed in its formation similar to that which produced the recent submarine vol

canos in its vicinity in 1638, 1720, and 1811. Had these taken place in shallower water, it is most likely they would have left some lasting heaps of volcanic products as monuments of the terrific power, which had been displayed there, similar to Monte Nuovo in the vicinity of Naples, and Jorullo in the province of New Spain, the last of which is more than sixteen hundred feet in height, and was the work as it were of a single moment. All of them were preceded by earthquakes and other terrific events, very much in the same way, and the materials thrown from them of a similar kind. Dr Webster's account of that near St Michael is too interesting not to be quoted.

In the months of July and August, 1810, this island was convulsed by repeated earthquakes. Slight shocks were also occasionally noticed till January 1811, on the last day of which month, about one o'clock in the morning, a shock far more powerful and terrific, than any which had preceded, was experienced; to this others succeeded, and they were repeated during the day in such rapid succession, that in the city of Ponta Delgada, thirtyone were counted in the space of a few hours. On the following day, a strong sulphureous smell confirmed the report, that fire and smoke had issued from the sea opposite to the village of Genettes, at the distance of about two miles from the shore.

The wind blowing from the westward, carried clouds of fine ashes towards the city, a distance of eighteen miles, where it was deposited upon the buildings and other objects. The column formed by the eruptive matter and smoke was seen by persons many miles farther to the eastward, rising above the intervening hills. Some of the pieces of lava were projected to the height of more than two thousand feet. When first seen above the water they were black, but, as they emerged from the column became red and glowing. Vast quantities of smoke, ashes, and water were ejected to the height of some hundred feet, but never rose so high as the stony masses. This eruption continued eight days, when it gradually diminished in activity and finally ceased altogether, leaving a shoal on which the sea broke.

On the tenth of June following, a sulphureous smell, attended with repeated and violent earthquakes, announced, that an eruption had again taken place, which was soon confirmed by the peasants from the western part of the island. The spot, whence the flames and ashes now issued, was about two and a half miles to the westward of that where the first eruption occurred, and at a distance of a mile from the shore, opposite the mountain, called the Pico das Camarinhas. The wind blowing off shore, carried away the smoke and allowed a perfect view of this grand phenomenon from the higher land.

'On the seventeenth the ejected matter became more abundant and the volcano appeared in its highest degree of grandeur, forming a vast column apparently of smoke and ashes; the eruptions were repeated in rapid succession, but with very regular intermissions. This latter circumstance encouraged some gentlemen to go off in a small vessel with the intention of sailing round the column; they were, however, unable to accomplish it, for scarcely had they set sail before they became enveloped in a dense, black cloud, from which poured down heavy showers of salt water and ashes, covering the deck of the vessel to the depth of more than an inch

The eruption having ceased, a small island was discovered to have been formed, which was estimated by those persons who observed it from the shore of St Michael, to be about a mile in circumference, and between two and three hundred feet above the surrounding water. After this it gradually increased. The north eastern extremity of the new island had a conical form; and on the other side was a deep hollow, or crater, into which the tide flowed, and from which flame rose for several days, attended with incessant explosions. The surf was too high at this time to allow any person to land, but from as near inspection as possible, the whole island appeared to consist of fine black ashes; very few large stones could be seen. The earthquakes now ceased, and the whole island soon after disappeared.'

Some of the circumstances mentioned by Capt. Robinson, in his account of the submarine eruption of 1720, are very similar to the foregoing, and prove them both to be of the same kind. He calls it an island all fire and smoke, and says that the ashes fell on 'the deck of his vessel like hail or snow all night-that the fire and smoke roared like thunder. Vast quantities of pumice must have been thrown out at this eruption, as it was seen not long after floating on the sea, as far as the coast of France. Mr Delisle, who communicated an account of the same to the French Academy, speaks of a very remarkable circumstance observed at that time. We quote it in the original On remarqua en meme temps que la pointe de l'ile de Pic, qui en etoit à trente lieues, et qui auparavant jettoit du feu, etoit affaisie, et n'en jettoit plus.' This indicates a subterranean communication throughout this volcanic region, such as has been thought to exist between Vesuvius and tna. The belief in the existence of such communications is connected with the theory of the origin of lavas. Those who suppose them to be formed by fusion out of the rocks of the interior of the earth, necessarily suppose large cavities to be