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.

f

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 ori ginally 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 moun tains 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 work→ "Tegi davracia axovata" 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 mo derns 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, (Oɛwy oxuα) had appeared to throw up sheets of fire that rose

ASCENSION.

even to the clouds, and that the sand of the sea was intolerably hot.

Now the mountain that went by this name is placed by Polybius south of the town of Lixus, a Carthaginian colony beyond the pillars of Hercules, and in the midst of the chain of Mount Atlas. Nor is it probable, that this antient navigator should have deviated so far from the coast, as would have been necessary, in order to enable him to catch a glimpse of the volcanic fires of Teneriffe.

It is remarkable indeed that the antients, although they have described the Canaries, under the names of Canaria, Purpurariæ, and Fortunate Islands, seem to have taken no notice of the volcanos that occur there. Even the Peak of Teneriffe is only alluded to in the mention of the perpetual snow found upon it, from whence the island obtained the name of Nivaria.

It is therefore most probable, that the description of Hanno refers to the Continent of Africa, and not to its islands; but before we decide that any thing of a volcanic nature is hinted at, we ought to recollect, that the customt which exists there, as in many other hot countries, of setting fire at certain seasons to the forests and dry grass, might have given rise to the statements of the Carthaginian navigator. Even in our own times the Island of Amsterdam was set down as volcanic from the very same mistake.

ASCENSION ISLAND.

The Island of Ascensiont is composed entirely of trachyte, and the rocks allied to it, which appear to have been

* Bory St Vincent thinks, that by the Purpurariæ, Madeira, and Porto Santo, were intended.

+ This is the opinion of the Abbe Gosselin in his Geographie des Anciens. See Ed. Phil. Journ. for January, 1826,

ST. HELENA.

thrown up in a dome-like form, and to have subsequently afforded a vent to vesicular, spumous, and corded lavas, by which they are frequently covered. On one of its hills, about 700 feet above the level of the sea, is a circular hollow, which has since been in great measure filled up. The beach is formed of a sand composed of comminuted shells, with fragments of echini and corals, which in parts near the sea is sometimes agglutinated by a calcareous cement into a pretty solid mass. The whole island has a most rugged and forbidding aspect. Its highest mountain is 2818 feet above the level of the sea, and is covered at top with pumice, having upon it a scanty covering of soil,

ISLE OF ST. HELENA.

It has been supposed by Forster, that the present island is only the wreck of a larger tract of land, submerged by the action of volcanos.

This however does not seem consistent with more recent statements, which lead rather to the idea, that the whole island has been raised above the surface of the sea by the same agency.

It would appear from Governor Beatson's account, that the volcanic matter rests on a substratum of sand, clay, and coral, which extends under the sea over a much larger surface.

The same remark applies to the Islands of Ascension and Tristan d'Acunha, and to Gough's Island.

Neither is there that general appearance of fracture and disturbance in the strata, which would have been observed had there been any truth in Forster's idea. The volcanic matter chiefly consists of a rock of a basaltic character,

* See Beatson's St. Helena, London, 1816.