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sixty miles south of Valparaiso, in the shells attached to the rock. Similar facts have further shown that the whole coast of the Pacific from Peru to Terra del Fuego has undergone this change of level. The parallel terraces, as at Coquimbo, which rise to the height of three hundred feet and more, have been found to be covered with seashells, indicating successive elevations. And this has not been effected by sudden and violent action only, but also by insensible degrees, as is now admitted to be the case in parts of Norway and Sweden, and in the island of Great Britain. The elevation of the coast of South America, which we believe first attracted notice, was attended with a terrific earthquake, but in the North of Europe along the coasts of the Bothnian Gulf the rise has been gradual, and unattended with any volcanic phenomena. Mr. Lyell has recently examined the marks, cut in the rocks by the Swedish pilots under the direction of the Swedish Academy in 1820, and found the level of the Baltic in calm weather several inches below them. He also found the level of the waters several feet below marks made seventy or a hundred years before. He obtained similar results in other places. He discovered deposits on the side of the Bothnian Glf, between Stockholm and Gefle, containing fossil shells of the same species which now characterize the brackish waters of that sea. These occur at various elevations, of from one foot to a hundred feet, and sometimes reach fifty miles inland. The result of this examination induced Mr. Lyell to declare his belief, that certain parts of Sweden are undergoing a gradual rise to the amount of two or three feet in a century.

The relative changes of level of the sea and dry land have been noticed in several other places, especially in the neighbourhood of Pozzuoli, of which M. Arago gave an account at the meeting of the Academy of Sciences on the 15th of May, 1837, together with the results of the observations of M. Capocci, Director of the Observatory at Naples. It is to be hoped, that this highly interesting phenomenon, connected with the physical history of the earth, will not be neglected by observers in this country, which has already presented so many new and important geological facts. Mr. Babbage has proposed an ingenious explanation of these phenomena, viz.

Fourth Report of the British Association for the Advancement of Science.

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the local changes of temperature in the lower strata of the earth; and has calculated that a change of 100° Fahrenheit that should affect a formation of sandstone to a depth of five miles, would cause an elevation at the surface to the extent of twenty-five feet.*

Before undertaking a description of these islands, our author should have made himself somewhat acquainted with the phenomena of subaqueous volcanoes, and would then have been saved the unsuccessful labor of bending facts to a preconceived theory. He must have seen in every island evidence of the repetition of eruptions, and ought to have been aware that such repetitions must have had the effect of raising the summits of the once submarine mountains above the level of the

According to the best observers, the limit of elevation has in many cases been attained, and hence we have these and other insular volcanoes. The observations of Humboldt and Von Buch, have led them to the opinion, that in submarine eruptions, the strata previously forming the bottom of the sea are uniformly elevated. Hence it is easy to account for the presence of the limestone in these islands, and the occurrence in it of fossil shells and impressions. But in some, the limestone is of more recent origin.

The great lateral extension of many of the beds of lava in these islands is one of the many evidences of their having flowed under the pressure of the ocean, as has been remarked in Iceland, the Ferroe islands, and others whose submarine origin is admitted by all observers. Where volcanic action has broken out since the elevation, the craters, or lateral openings and dykes, are everywhere seen. In some of the beds of lava, the vessicles or air bubbles are of prodigious size, two or more feet in diameter, and those of smaller size are everywhere met with, even in the hardest and most compact lava, while that in which they are so numerous as to give the lava the spongiform and cellular aspect, occupies the sides of the hills or covers large tracts of surface. The hills and mountains with which the islands abound, marking the sites of eruptions, and the plateaux composed of compact lava and tuff, or covered by pumice and scorified fragments, with blocks of obsidian, still farther indicate a submarine origin, and render the resemblance to Iceland and the islands already referred to still more striking.

* Edinburgh Philosophical Journal, Oct. 1837.

The interpositions of beds of scoriæ and tuffa, which are to be seen in the most distinct manner alternating with the beds of basaltic lava all along the coasts, in bold precipices, indicate a series of ejections at successive intervals. In some of the islands, high bluffs are composed entirely of very hard, light-colored tuffa, which, as at Fayal, might be mistaken for sandstone; in other places detached masses rise in pinnacles above the waters, or have been cut through by the action of the waves, presenting the most picturesque appearance. Some of them are arched and the waters flow beneath.

Great changes on the surface are going on at this day. Within the recollection of many of the inhabitants, torrents of water have rushed from the mountains, carrying destruction in their course, overwhelming cottages and cultivated spots with huge masses of rocks, pumice, and loose earth. There is one spot in St. Michael's, several acres in extent, which was verdant and cultivated, until on a sudden the whole surface was covered with huge fragments borne down in the course of one night, and it is now a barren waste of loose rocks. In another spot, on the side of a deep ravine, at the bottom of which flowed a small stream, an enormous mass of pumice, an acre or two in extent and several hundred feet in thickness, suddenly separated from the main body, which formed an extensive plain, and fell into the ravine, leaving a yawning and frightful chasm. In Madeira these destructive effects have been more common and terrific than in the Azores. The effect of a most frightful flood, which occurred in 1803, has been described by an eyewitness, when such a swelling of the rivers took place, that they shortly rose and overflowed their banks, rushing down the declivities, and sweeping away whole vineyards and plantations, cattle, wine, stores, and the houses of the inhabitants, who, with their whole families perished. Rocks of enormous size, as well as the largest trees, torn up by the roots, were carried from the mountains to the sea. The vestiges of this dreadful flood are still to be seen. A crater, said to be about three quarters of a mile in circumference, had a segment of its larger circumference, with the trees growing upon it, borne down into the bottom of the crater. In the town of Funchal, whole lines of houses with their inmates were swept into the sea, churches, bridges, and edifices of every description were involved in the same general wreck. It was computed that no less than three hundred persons perished.

The action of the waves is continually producing changes along all the coasts, the interposed beds of tuff and cinders are washed away, and the compact beds of lava being left unsupported, fall. The shores are strewed with huge blocks and fragments of all sizes.

Did not the geological structure of the islands furnish abundant evidence of volcanic action, we find it on record in the islands, and in one of the earliest works, that eruptions and earthquakes have occurred at various times, as well within the recollection of living witnesses as at earlier periods.

The first earthquake of which we have been able to find any record was on the 25th of October, in the year 1522, when five thousand persons were destroyed. It occurred at daylight, and was particularly violent in the district of Fanaes da Ajuda and Maia, on the north coast of St. Michael's. It extended to a considerable distance, nearly destroying the large city and port of Villa Franca. A large part of the town was laid in ruins, and the Franciscan convent and other buildings were overwhelmed by a torrent of ashes and mud which has since become consolidated into a compact tuffa. Although the destruction of this place is now always attributed, by the present inhabitants, to an earthquake, it is beyond doubt that an eruption took place, of which we find traces in the compact lava covering the tuff and running out into the sea, forming indeed a wall with points here and there appearing above water, and resembling somewhat a coral reef, in front of the town. There is also in front of the town an island of tuff in distinct strata, dipping towards the interior in the form of a washing basin.*

In 1563, on the 25th of June, the whole island of St. Michael's was convulsed with an earthquake, which was most seriously felt in the neighbourhood of Ribeira Grande. An eruption appears to have taken place near the centre of the island; and the hill formed, which has now the name of Mount Vultur, exhibits abundant evidence of this event. The lava flowed in a current chiefly to the West, and covered Cabuco with porous lava; a tract which still remains uncultivated. At this time a large crater, called Lagoa do Fogo (or Lake of fire), twelve and a half fathoms deep, was formed.

An eruption also occurred on the 2d of September, 1630,

See a plate and description of this island in Daubeny on Volcanoes, copied from Dr. Webster's work.

in the valley of the Furnas, and the spot is now a nearly circular plain surrounding a somewhat high hill with a crater at top. At this time the cinders were carried nearly ninety leagues, as far as Terceira.

Since then other eruptions of minor importance have taken place from the same spot. On the 10th of October, 1652, the elevated Pico do Fogo was raised, and on the 19th of the same month, the hill called Pico de Ja› Ramos, northeast f Lugar de Rosto de Cão in St. Michael's. July 3d, 1638, was an eruption from the sea off Pico das Camarhinas, at the distance of one league from land, and where there were forty fathoms of water. In 1691, there was an eruption off St. Michael's, and another in 1720, producing an island six miles in circumference. Many earthquakes occurred in the autumn of 1810. On the 1st of February, 1811, was an eruption off Genetes; and on June 13th occurred another, about a mile from the island of St. Michael's, which elevated the island called Sabrina, described and depicted in Dr. Webster's work. The same phenomena have since occasionally recurred, but there has been no actual volcanic eruption in St. Michael's. In the island of St. George a destructive eruption happened in 1808, which is also described by Dr. Webster.

In the Count's meagre notices of the other islands, there is nothing which demands notice. We should perhaps make an exception in regard to Flores, where he professes to have discovered a vein of zinc !-more primitive rocks, - the "schisto argilloso primitivo" again; and "grandes depositos de barro proprio para cachimbos," which may be translated pipe clay, enough for all the smokers, of whom there is no deficiency, in the islands; - a discovery (this last) so far exceeding in importance any other recorded in the "Resumo," that its author deserves from the grateful Azoreans a perennial monument of pipe-stems.

In a word, all the geological phenomena, which have been remarked, lead to one and the same inference in regard to the volcanic origin and causes of the present aspect of the remaining members of this archipelago, and lend no support to the theory of subsidence. We do not hesitate to express our opinion, that not only Madeira and the Azores, but also the Cape de Verds and Canaries have had a similar origin, and are to be viewed as belonging to the third class in Mr. Scrope's arrangement of volcanoes; in which are also comprised many

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