Of the Azores we have lately obtained a geological account from my friend and fellow-student Dr. Webster, of Boston, in the United States.*

The Island of St. Michael, the largest of them, is described by him as entirely volcanic, and containing a number of conical hills of trachyte, several of which have craters, and appear at some former period to have been the mouths of so many volcanos. The trachyte is completely covered by the ejections of pumice and obsidian that have proceeded from these sources, and it is seldom that we are able to discover it, except in the ravines, or on the summit of the hills.

This rock however, so far as I can collect from Dr. Webster's description, does not constitute the fundamental stratum, it has rather been forced through strata of tuff and of basalt, which extend over the island, covered however in most places by the ejections of pumice and obsidian. Dr. Webster notices likewise a description of lava which he compares to the cavernous variety mentioned by Sir G. Mackenzie; it is swollen into large blisters and other irregularities, and contains several remarkable caves, from the roof of which hang stalactites, as they may be termed, of lava, which assume a variety of curious arborescent figures.

The Island of St. Michael is famous for its hot springs, which are impregnated with sulphuretted hydrogen and carbonic acid gases, thus seeming to attest that the volcanic action is still going on. Of this however, evidences have, within the present century, been afforded of a far more 'direct and positive nature. In the year 1811 a phænomenon occurred, similar in kind to that, which I have already described as having happened in the Grecian Archipelago. After a succession of earthquakes experienced more or less sensibly in all the neighbouring parts, a new island arose in the midst of the sea, of a conical form, and with a crater on its summit, from which flame and smoke continually issued. The island, when visited soon after its appearance by the crew of the frigate Sabrina, was about a mile in circum

* Webster. Description of the Island of St. Michael, &c. Boston, 1822.

ference, and two or three hundred feet above the level of the ocean, it continued for some weeks, and then sunk again into the sea.*

A singular phænomenon occurs at a short distance from the coast near the town of Villa Franca, which has all the appearance of the crater of a volcano half sunk below the level of the water. It consists of a circular basin, the interior of which contains enough water to float a small vessel, but the sides are elevated 400 feet above the sea. The basin is perfect except on one side, where the depth of water is sufficient to allow a ship to enter, and it would ride securely in the interior, were it not for a sinking of the basin on one side, which allows of the sea breaking over it, when the wind is in a south-easterly direction.

The sides of the basin consist of tuff, presenting an abrupt precipice externally, but dipping in a more gradual manner towards the interior, and Dr. Webster observes that the strata all slope towards the interior and not towards the circumference, so that the structure is the very reverse of that described by Von Buch as belonging to the waters in the Canary Islands, and the circular cavity must in this case have been formed, not by an uplifting, but by a subsidence of the strata.

The following sketch may represent the appearance of the basin.

Humboldt (Pers. Narr. vol. i. p. 243) remarks, that the formation of the

island was anterior to that of the crater.

There also occurs in the midst of the sea a pyramidal mass of tuff only 30 or 40 feet in diameter, consisting of horizontal strata from one to two feet in thickness. It is evidently the remnant of a formation, the greater part of which has been washed away, and seems to be analogous to that which I have noticed, as occurring in the valley of the Puy en Velay, in the south of France.

The other islands belonging to the same groupe appear to be similarly constituted. That of El Pico is the only one which contains a volcano at present in activity, for the great currents of lava which flowed in 1812 from the adjoining island of St. George, are considered as the results of a lateral eruption from this volcano. The summit of El Pico is no less than 9000 feet above the sea; it consists of a conical mass of trachyte, and is constantly emitting smoke.

It may perhaps be inquired, what degree of light geology is capable of affording with respect to the existence of a former continent or large island, serving to connect Europe with America, which the antients sometimes allude to under the name of Atlantis.

It might appear at first sight, that the knowledge we have of late obtained with respect to the physical structure of the islands, which in such case must be regarded as the relics of this submerged country, lends some weight to the historical evidence in favour of its existence, since the volcanos that are proved to be in action in so many parts of the intermediate tract of ocean, might afford an adequate explanation of the effect supposed to have taken place.

. But on the other hand, when we examine more narrowly into the appearances presented in those islands which I have been describing, we shall find it greatly more probable that they have been separately raised from the bottom of the sea by volcanic agency, than that they have been severed apart, after having once constituted a single continuous tract of land. The details which I have extracted from Von Buch's interesting memoirs lead inevitably to this conclusion, as

they tend to demonstrate, that the strata which form the basis of these islands, and through which the volcanic cones, where such exist, have been protruded, were formed originally at the bottom of the sea, and have been afterwards heaved up by the elastic vapours acting from beneath.

It may be alledged indeed, that the whole of these islands do not consist of volcanic matter, for Gomera, Fortaventura, and others, contain rocks either consisting of primitive materials or of limestone, but the rare occurrence of the latter over a tract so vast, as that which the Continent of Atlantis must be supposed to have occupied, certainly lends but little countenance to the hypothesis. It may be remarked too, that volcanos seem much more active in building up strata than in destroying them, and that, if they had operated on so extensive a scale as must be assumed by those who attribute to their agency the destruction of a continent, they would on the other hand have raised up more extensive tracts of volcanic materials in the place of those they had been the means of subverting. It is suffi cient to cast a glance over the conjectural map of the Atlantis, by Bory St. Vincent, to be convinced of the absurdity of any such hypothesis, for who can imagine a tract of land extending from 40 to 15 N. latitude, having for its northern boundary the Azores, for its southern the Cape de Verde Islands, and for its eastern promontory the Peak of Teneriffe, to have been swallowed up in the ocean by any causes now in operation, or at any period since the creation of man.

*

For my own part, were I persuaded that the Atlantis of the Greeks referred to any thing real, and was not throughout a figment of the imagination, the hypothesis I should be most inclined to adopt, is that proposed by Ali Bey in his Travels. We find it there stated, that the whole of the flat coast towards the Atlantic Ocean is caused by the wash

See Bory St. Vincent sur les Iles Fortunées.

+ Tom. 1. p, 36-37.

MOUNT ATLAS.

ings of the sea, by the ground sand carried into the ocean, and by masses of clay which he considers as the product of some submarine volcano. These materials together form a sort of tufa, upon which beds of marl and of animal exuvia have since been deposited. He finds these desert strands on the whole of the southern border of the table-land of Mount Atlas, towards the deep-laying flat of the Sahara, and extending as far as the Syrtis, and therefore supposes, that at some former period the elevated ground of Mount Atlas may have constituted a sort of island-perhaps that of Atlantis.

This notion as to the volcanic origin of certain parts of Mount Atlas, is borne out by the existence of some mountains in the same chain, called Black Harusch, which are conjectured to be of an igneous nature.

It would also appear from the author of the work66 Περι θαυμασιων ακουσμάτων” vulgarly attributed to Aristotle, that the Greeks regarded the whole of the coast of Africa beyond the Pillars of Hercules as thrown into disorder by the fire of volcanos, and Solinus expressly states that the snowy summit of Mount Atlas glitters with nightly flames; so that we might be led to infer, either that this mountain was situated in one of the islands of the Hesperides, and was probably identical with the Peak of Teneriffe, or that some volcanic appearances exist in the chain which the moderns speak of as Mount Atlas.

In the account of the Periplus of Hanno, as well as in that of Eudoxus, as quoted by Mela, (which is considered a fabrication, and a direct copy of the former,) we read, that as these navigators were coasting in the above direction along this part of Africa, torrents of light were seen to fall on the sea, that every night the shore was covered with fires, that the Great Mountain, called the Car of the Gods, (ewv oxux) had appeared to throw up sheets of fire that rose