kind of immense ridge abounding in rocks, partly hidden in the depths of the sea.

"The Azores appear to be formed almost of trachytic masses; basalt is nowhere found among them except in the little islands of Corvo and Flores, which are yet imperfectly known. This kind of rock is described by Webster, and in the accounts which have been lately published on the eruptions of the islands of St. George. Mr. Dabney, American Consul at Fayal, has addressed a letter to the United States, in which he gives a description of volcanic phenomena of the Island of St. George. He says, "On the 1st of May 1808, the ground, three leagues to the north-east of Velhas in the north-western part of the island opposite the isle of Pico, was rent with a noise similar to the discharge of cannon, and formed in the middle of cultivated fields an immense crater of twenty-four acres in extent. In the space of two days this erater threw up such a quantity of scoria and pumice stones that the ground was covered with them from one to four feet in depth in an extent of three leagues long, and one broad. On the 2nd of May, another opening formed itself a league to the north of the former, and at a distance of two leagues from Velhas. This crater might be approached and was found to be formed of a great quantity of small fissures, often six feet wide, traversing the ground in all directions. The crater was about 150 feet in circumference. On the 5th of May, and following days, twelve or thirteen small craters were also formed in the same place from which a great quantity of lava flowed towards Velhas. It is very likely that this mass was formed of obsidian, for it was preceded by an eruption of pumice stones, and these two matters evidently indicate the presence of trachyte in this island.

"On the 11th of May the lava ceased to flow, and then a fresh and violent eruption took place from the first crater, and was seen at Fayal until the 5th of June emitting a burning current, which descended the sides of the crater and fell into the sea, after which it became tranquil. This immense crater is four English miles from the shore, and is nearly 3,500 feet above the level of the sea. Before its formation, no part of the island was so high as that."

"Fayal appears to be nothing more than a part of Pico, for the general direction of these islands and their shores perfectly corresponds. The island appears to have a crater in its centre. Webster says that the highest part of it is 3,000 feet, and that the sides of the mountain have a gentle acclivity up to the caldera, that it is five miles in circumference, with four to five feet of water in it. The Swedish Lieutenant Hebbe, considers it two leagues wide. It appears doubtful that this caldera was formed, as Adanson says in the last eruption of Fayal, in 1672. Labat also says, that in this year the eastern side of the mountain opened, and a stream of lava flowed from it, and destroyed 200 acres of the best land. Notwithstanding the numerous observations made on this island, the component parts of the rock of which it is formed are unknown.

"The island of St. Michael is notorious for the various islets which have attempted to raise themselves in its neighbourhood, on the side opposite to Terceira or St. George. On the 11th of June, 1638, an isłand appeared two leagues and a half in extent, and more than 360

feet in height. On the 1st of December, 1719, another was formed, which disappeared in 1723, this was twelve miles and a half from the land, the same phenomenon appeared in 1811. In this year, the bottom of the sea was raised in two different places, which were little known. Previously in the month of August, 1810, the whole island of St. Michael, ascording to Webster, had been shaken by an earthquake. On the 31st of January, 1811, a violent shock, and a strong sulphureous smell, announced that a submarine explosion had taken place at the western extremity of the island, and at two miles distance from the shore, opposite the town of Ginetas, large volumes of smoke and cinders and water were thrown up from the sea, and formed a grand column several hundred feet high. The stones which accompanied the eruption, were thrown a considerable height nearly 2,000 feet. When first thrown up from the sea they appeared black, but scarcely had the anass of smoke passed away, than they became red and burning, evidently the consequence of a combustion in the atmosphere of the metallic matter of which they were probably formed. The eruption continued for eight days; when it ceased, a shoal was formed in the sea, on which the surf broke in a place where there was before from sixty to eighty fathoms water.

"On the 13th of June, a second eruption took place a mile and a half from the first, and a mile from the shore opposite the peak of Camarinhas. The result of this eruption was the island of Sabrina, about a mile in circumference, and 300 feet high. This island had a well formed crater, open to the south-west, and from which a current of hot water ran towards the sea. It was terminated by a ridge as other craters generally are. The opening was thirty feet wide. Captain Tillard who visited the crater on the 4th of July, and gave it the name of his vessel, has sketched it as seen from the shore. The plan and view are published on one sheet by Boydell, of London, May, 1812. In a note accompanying the plate, the author adds, that he learnt from the English consul, Mr. Read, that towards the month of October, the island commenced sinking gradually, and about the end of February, 1812, nothing more than vapour was occasionally seen issuing from that part of the sea where it had been formed.

"The remarkable island of Porto de Ilheo, near Villa Franca, is quite analogous to that of Sabrina, and has certainly the same origin. In the middle of this island is a crater, into which vessels may enter by an opening similar to those which especially characterize this kind of crater. Views are given of this island in the history of the Azores, 1813, (page 80-82, Thomas Ashe,) and on the excellent chart of St. Michael, by Mr. Consul Read, published in London, in 1808. Webster says, (page 186,) that the brink of the crater is 400 feet high, and is composed of a sandy substance, in which fragments of lava, scoria, and pumice stones are found. No part of the sides of the crater is formed of solid rock.

"Notwithstanding that the numerous hot springs of the island of St. Michael, are unequivocal proofs of constant volcanic action, this island has no volcano, but three immense craters may be distinctly recognized in its whole extent. That in the north-west part of the island is the largest. It is 2,000 feet high, and its circumference about six leagues

in extent. It appears quite analogous to the lake of Laach, near Coblentz. The interior of the crater is occupied by two lakes, the Lagoa Grande and the Lagoa Azul, which communicate with each other. The sides of the crater are composed of loose pumice stones, below which is the sandy substance found at the sea side. At the bottom only trachytic rocks are found, containing vitreous feldspar, and long chrystals of hornblende.

"The second crater is the Lagoa de Pao, situated in the middle of the island, and in a large mass of pumice stones. At the foot of the crater, towards that part of the coast where the town of Agoa de Pao is situated, a rock en place is found, in which augite* predominates, but masses of trachytic conglomerate soon appear in the deep gorges on the sides of the mountain. In the midst of these conglomerates, large blocks about twice the size of the head are found, formed by a mixture of large chrystals of feldspar and hornblende, and a little oxydized magnetic iron, similar to that of granite, and probably the same as the rock found at Santa Maria de Bethencouria, in the island of Fuertaventura, or in the Caldera de Palma. These blocks are nowhere found en place. The greatest part of the mountain round the Caldera is formed of pumice stones, containing chrystals of feldspar. A rock named the mountain of Agoa de Pao, according to barometric observations, is 3,463 Paris feet above the level of the sea.

"The third crater, called Alagoa das Furnas, in the middle of which are hot water springs, is not so high as that of Alagoa Grande. It is also surrounded by a considerable mass of loose pumice stones, which appear to form throughout a great extent, the principal mass of the whole island in which basaltic rocks are almost entirely wanting. On the northern coast only, and a little to the north of Punta del Ajuda, at low water a rock appears, divided into ill-formed pentagonal columns, the principal mass of which is black, like the basalt of Saxony.

"The whole, is probably, a great ridge in which trachytic rocks have been changed into obsidian or pumice stones, the divisions of which are formed by basaltic rocks concealed by the sea. From Alagoa das Furnas the mountains of pumice stone continue higher, forming a continual range as far as the Pico de Vara, the height of which is estimated above the sea 5,000 feet. This is the only summit in the island where snow is found.

"The description of these islands by Capt. Boyd, contains many important facts respecting their physical formation. It cannot be doubted that this Archipelago, which extends from south-east to north-west

* The following note on augite is from an elaborate article on the subject in the Penny Cyclopædia.

"AUGITE.-The minerals to which this name has been applied, present us with the most interesting and at the same time most difficult investigations that can fall under the notice of the mineralogist and chemists, and have frequently occupied the attention of the most eminent men in both sciences. Nor are these bodies unworthy of such attention. For not only would a thorough knowledge of their constitution, and the relation they bear to other minerals, particularly to the genus hornblende, tend much to the perfection of the mineralogical system, but owing to their frequent occurrence in nature, and from their forming one of the principal ingredients in many porphyritic and trap rocks, such as the syenite diallage and chorl rocks, green stone, &c.; they form a class of bodies of the highest importance to the geologist."

must be considered as an immense ridge on which craters are thrown up so as to form islands, for Capt. Boyd even gives us the boundaries of it. The island of St. Mary, the only one not situated in the general direction of the others is not volcanic: no part of its surface appears to have suffered from heat or eruption subsequent to its formation. The whole island is composed of beds of schiste in a position nearly perpendicular, and which form steep precipices on the coast. In the north-west part of the island in a place inaccessible, an immense bone of a large animal may be seen projecting from the schiste rocks. It is covered with a calcareous formation full of marine remains, and from which lime is obtained apparantly of recent formation.

"Few islands display such a variety of volcanic phenomena as the islands of St. Michael, although a real central volcano is never found there in action. After Gonzalo Velho Cabral had succeeded in establishing a colony in the island of St. Mary discovered in 1431, he landed in 1444, on the north-west coast of St. Michael, and the extensive plains which he saw appeared to him so capable of being highly cultivated that he returned immediately to St. Mary to make his preparations for colonizing this newly discovered country. But when he went there the following year with everything necessary for the establishment of his colony, what was his surprise when in the place of the plains he found an enormous mountain, which had been elevated on them, with an immense crater. Torrents of water, mud, stones, scoria, and cinders covered the sides, and spread over the neighbouring parts. This mountain with its crater is called the Alagoa de las siete Cidades, on which are two lakes. The circumference of the mountain is fifteen miles, and its height above the level of the sea about 2,000 feet. From that time no eruption has taken place from the crater, or from the sides of the mountain. Here then is a crater of the most decided character. If it had forced its way through the sea it would have formed an island as large as Graciosa, and little less than Fayal. This mountain then is the result of a great volcanic action which has been only once exerted, but which has established no continuous communication between its internal fires and the atmosphere.

"Capt. Boyd gives a list of the eruptions of St. Michael which deserves attention; it may be seen at once that the orifices of these eruptions are continually changing, and do not shew any tendency to a common

crater.

"After the elevation of Alagoa de las siete Cidades, the island remained tranquil. In 1522 an eruption hurled into the air the two hills, Sorical and Rubacal, and covered the town of Villa Franca, which was entirely destroyed. Four thousand inhabitants lost their lives on this occasion.

"In 1563 there was an eruption of the Pico Sapadeiro. A large current of lava ran into the sea on its northern side near Rebeira Secca. "In 1638, a large island appeared fifteen miles to the west of St. Michael, it remained quiet for several years, and then disappeared suddenly, leaving in its place a fathomless ocean.

"In 1652 the hills of Pico do Foro, Romos, and Pico do Paya, to the north-east of Rosto de Cao, near Punta Delgada, threw up an immense quantity of stones and cinders, spreading destruction over the surrounding country.

"In 1691, after some very violent earthquakes several small islets appeared not far from the coast.

"In 1719, a new island appeared fifteen leagues west, its diameter was nine miles, and it disappeared in 1723, leaving seventy fathoms water. "The great earthquake of Lisbon in 1755 was felt at St. Michael by severe shocks without an eruption.

"On the 11th of August, 1810, violent motions of the earth were felt. In the northern part of the island fire burst from the fissures, and there was an eruption of the peak of Genates in the south-west part of it.

"On the 13th of June, 1811, the island of Sabrina appeared and disappeared in the month of October. From that year till 1835, the island remained undisturbed.

"The island of Terceira has a crater, six miles north-west of the town of Angra. Large fissures on the sides of the mountain emit vapour in abundance. These fissures were formed after the earthquake of 1614, by which the town of Praya was destroyed. From that time these phenomena have ceased on the island. The crater is called Furnas d'Euxofres; it appears to be entirely surrounded by hills of pumice stones. "Captain Boyd states, that these stones frequently fall and throw down trees, which being buried beneath them, make it appear that they were surrounded by the eruption of these stones. A single eruption which took place in 1761, poured forth lava from the peak of Bagacina, which after running a league in extent fell into the sea.

"The island of St. George, so close to the central volcano of Pico, is also the most agitated. An eruption in 1580, a league and a half from the port of Velhas, lasted several days, and numerous currents of lava ran into the sea, where it formed an indented and steep coast. In 1691, eruptions appeared in the sea. Many small islets appeared near the coast, but disappeared soon after. This phenomenon occurred again in 1720, the year in which the island* appeared at the south-west extreme of St. Michael, and about a mile from the shore; and in 1757, eighteen small islets appeared about a thousand feet from the coast, which after a few years disappeared. In May, 1808, the great eruption took place described by Mr. Dabney.

"The eruptions of Pico itself confined themselves in 1572 to the eastern side; a stream of lava escaped from the mountain and fell into the sea, six miles distant near the town of Prainha. In the same century, two other eruptions were accompanied by currents of lava, one, ran to the northward near Bardeira, the other to the southward, not far from St. Mateo. The last eruption of 1718, took place on the western side.

"The view of the peak, which Captain Boyd gives by Admiral Sartorius, displays as much taste as faithfulness of representation. Captain Boyd states positively, that the current of lava that ran over the island of Fayal, in 1672, escaped from the sides of the peak, not far from the town of Praya, and that it did not descend from the sides of the crater, in the middle of the island where there are no appearances of lava."

* This island, which appeared in 1720, is either the same, or another which is described farther on in the Philosophical Transactions for that year. If the last, it is much nearer to the island of Terceira than that of St. Michael, as the latitude and longitude assigned to it clearly shew.-ED. N.M.