and again suddenly resume all their former character. Thus Vesuvius, which had been extinct from time immemorial, although its crater was clearly formed by some ancient volcanic action; suddenly rekindled in the reign of Titus, and buried the cities of Herculaneum, Pompeii, and Stabiæ, under its ashes. After this effort it again slumbered, the memory of its former power faded away; trees and grass grew on its summit, when suddenly in 1630, it renewed its action. At this time, the crater, according to the account of Bracini, who visited Vesuvius not long before the eruption of that year, "was five miles in circumference, and about a thousand paces deep; its sides were covered with brushwood, and at the bottom there was a plain on which cattle grazed. In the woody parts wild boars frequently harbored. In one part of the plain, covered with ashes, were three small pools, one filled with hot and bitter water, another salter than the sea, and a third hot but tasteless." Suddenly, in December 1630, these forests and grassy plains were blown into the air, and their ashes scattered to the winds; seven streams of lava poured at the same time from the crater, and overflowed several villages at the foot, and on the side of the mountain; since that time there has been a constant series of eruptions. Etna after slumbering for ages, burst forth and destroyed the city of Catania; the accounts of its previous eruptions having been considered by the inhabitants as fables.

Subterranean noises, and the appearance, or increase of smoke, are the first symptoms of approaching volcanic action. This is soon accompanied by a trembling of the earth, and louder noises; the air darkens, and the smoke, thick with fine ashes, increases. . The stream of smoke rises like an immense black shaft, high up into the air, and arriving at a point where its density is the same as the atmosphere, spreads out like a vast umbrella, overshadowing the whole country with its dark gloom. Such was the appearance as described by Pliny, the Elder, who witnessed the eruption of Vesuvius which overwhelmed Pompeii, in A. D. 79. Occasionally, lightning flashes illuminate the dark cloud, and streams of red hot sand, like flames, shoot up into the sky, attended with loud explosions. The shocks, and tremblings of the

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ground, increase, and the whole neighborhood gives evidence of the immense pressure which is being exerted; presently the molten lava, is by the immense force raised into the crater, and filling it up, or melting its passage through the side, flows in a red hot stream down the flanks of the mountain in a river, or rather a torrent of fire. The eruption is sometimes attended with enormous currents of water, mud, and noxious gasses. A period of rest succeeds, generally of short duration; again the same phenomena are repeated, and thus the action continues for a variable length of time, until finally, the crisis is past and the volcano resumes its original quiet.

The substances principally ejected by volcanoes are smoke, ashes, sand, scoriæ, volcanic glass and bombs, and masses of rock. The ashes thrown out in volcanic eruptions appear to be the substance of the lava very finely divided. These ashes are raised so high that they are carried by the winds to almost incredible distances. Ashes from the eruption of a volcano in St. Vincent in 1812, were carried twenty leagues, and fell in Barbadoes, and from the eruption of Hecla in 1766, they fell in Glaumba, a distance of fifty leagues; and it is said that ashes from Vesuvius have fallen in Constantinople, a distance of four hundred and fifty leagues. The volcanic sand, is composed of particles somewhat larger, but of the same character as the ashes, being comminuted particles of lava, and forming a principal part of the ejected matter of volcanic eruptions. Scorice, and pumice stone, are caused by the gasses, which bursting through the melted lava, carry up with them certain portions into the atmosphere, which becoming consolidated, present the appearance so well known under the name of slag and cinders. Volcanic glass or obsidian, is often ejected in small melted masses; sometimes, the winds catching this, spin it into the finest threads. We have seen many specimens of this kind from the eruptions of Kirauea, in the Sandwich Islands. Among the extinct volcanoes of France, drops, tears, and elongated spheroids, being drops of lava thrown out, and consolidated in the air, are continually found, they are called volcanic bombs. Masses of rock are always ejected in severe eruptions; in many cases these are undoubtedly torn off

from the interior of the mountain by the immense power exerted; and they are ejected without having been melted. A stone of 109 cubic yards in volume, was ejected by Cotopaxi, and thrown to a distance of nine miles.

The force which is exerted, to cause the eruptions of lavas, or liquid masses of stone, is almost beyond belief, varying according to the height of the crater. The force of Vesuvius in some of its eruptions has been estimated as equivalent to a pressure of at least 6000 pounds on every square inch; and of Etna, about 17,000 pounds on the square inch; the amount of force requisite to raise melted lava to the crater of Cotopaxi, would be at least 30,000 pounds on each square inch. The masses of melted matter ejected, are equally incredible; the amount thrown out by Vesuvius in 1737, was estimated at 11,839,168 cubic yards, and about twice this amount in 1794. In 1660, the mass of matter disgorged by Etna, according to Mr. Lyell, was twenty times greater than the whole mass of the mountain, and in 1669, when 77,000 persons were destroyed, the lava covered 84 square miles. The greatest eruption of modern times, was from Skaptar Jokul, in Iceland, in 1783. Two streams of lava, one fifty miles long and twelve broad, the other forty miles long, and seven broad; both avaraging 100 feet in thickness, and sometimes 500 or 600 feet, flowed in opposite directions, destroying twenty villages, and 9000 inhabitants. The velocity with which the melted lavas move varies with the slope of the mountain, and the nature of the ground, as well as the viscidity and quantity of the lava. In general, a velocity of 400 yards an hour is considered quick, although sometimes the stream flows much quicker; in flat grounds it sometimes occupies whole days in moving a few yards. Lavas cool extremely slow, the surface becomes soon consolidated, and is such a poor conducter of heat, that the interior remains heated and melted for whole years; and currents have been mentioned which were flowing ten years after emerging from the crater, and they have been seen smoking twenty years after an eruption of Etna. The currents of lava thrown out by successive eruptions being placed one above the other, alternating with beds of sand, scoriæ, &c., form a series of inclined beds that give rise to the cone of the mountain,

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Having now described the principal phenomena attending volcanic eruptions, and the nature of the erupted materials, we proceed to describe briefly some of the more remarkable effects of volcanic agency. Southern Italy, being inhabited by a cultivated people, and in very early times the seat of literature and science, as well as the grand European seat of volcanic action, claims particular attention. Here are three active volcanic vents. Vesuvius near Naples, Stromboli on the Lipari Isles, and Etna in Sicily. The whole region is subject to earthquakes, and abounds in thermal springs impregnated with calcareous matter, and from certain fissures deleterious gasses and sulphureous flames issue. The ancient name of Vesuvius, was Somma; it is now a broken and irregular coue about 4000 feet in height. We have already given the description of this mountain as it appeared before the eruption of 1631. It is said that its cone was formerly of a regu lar shape, with a flat summit, containing the remains of an ancient crater, and covered with wild vines. After a slumber of ages, Vesuvius in the year 63, began to exhibit some symptoms of internal agitation, by an earthquake which occasioned considerable damage to some of the neighboring cities. It is somewhat remarkable that the memorials of this convulsion have been preserved, and made known, through the agency of another more terrible convulsion, that of August 24th in the year 79, when a tremendous eruption occurred, and the pent up melted materials of the volcano burst out, overwhelming three cities and many of their inhabitants. Two of these cities, Herculaneum, and Pompeii, have since been exhumed. The former was first discovered; but they had long been forgotten. The eruption which destroyed these cities was witnessed by both the Plinys, and indeed, it was from his too venturesome curiosity to observe this magnificent natural exhibition, that the elder Pliny lost his life, being suffocated by the sulphureous vapors. The account which Pliny the Younger has left of this eruption, is very full and minute; but he makes no allusion to the overwhelming of the two cities. In 1713, Herculaneum was accidentally discovered, having been buried in lava for 1634 years, Some fiagments of inarble were observed in sinking a well; and subse

quently a small temple, and some statuary.

The city of Portici is built upon the lava directly above Herculaneum, and this has prevented extensive excavations. Pompeii was enveloped in ashes and cinders, and has been opened to the light of day. Both these cities were sea-ports, and Herculaneum is still near the shore, but Pompeii is at some distance, the intervening land having been formed by volcanic agency. In both these cities inscriptions were found in the temples commemorating the event of their rebuilding after having been overthrown by an earthquake sixteen years before, A. D. 63. Thus, in the language of Bulwer, "After nearly seventeen centuries had rolled away, the city of Pompeii was disintered from its silent tomb, all vivid with undimmed hues; its walls fresh as if painted yesterday; not a tint faded on the rich mosaic of its floors; in its forum the half-finished columns, as left by the workman's hand; before the trees in its gardens thesacrificial tripod; in its halls the chest of treasure; in its baths the strigil; in its theatres the counter of admission; in its saloons the furniture and the lamp; in its triclinia the fragments of the last feast; in its cubicula the perfumes and rouge of faded beauty; and everywhere the skeletons of those who once moved the springs of that minute, yet gorgeous machine of luxury and of life."

We here present a view of Vesuvius from Sir Wm. Gells Pom