wide, and six hundred deep, forming barriers by which rivers were dammed up and lakes formed. North of Quito, in the provinces of Pasto and Popyan, occur six other volcanoes; and in the provinces of Guatimala and Nicaragua, which lie between the isthmus of Panama and Mexico, there are no less than twenty-three volcanic mountains, all of them situated between the 10° and 15° of north latitude, some of which are constantly in an active state.

This great volcanic chain, after being thus -extended from south to north, nearly in a direct line, is continued through a great part of Mexico, from west to east. Here are five active volcanoes, known by the several names of Tuxtla, Oribaza, Popocatepetl, Jorullo and Colima. Still north of Mexico, in the peninsula of California, there are at least three, and according to some, five burning mountains.

Thus we see that this volcanic chain extends nearly in an uninterrupted course from Chili to the north of Mexico, a distance of nearly 4000 miles.

Another continuous volcanic range, of nearly equal extent, begins at the Aleutian Islands, belonging to Russian America, and by a circuitous route, passes to the Molucca Islands. Through this whole extent, earthquakes of the most terrific description are common.

But our limits will not permit the enumerrtion of all the volcanic tracts described by authors. Besides those already mentioned, Kamtschatka has seven burning mountains; the island of Java contains thirty-eight great volcanoes; the Molucca Islands contain several, and among them that of Sumbawa, which, in 1815, suffered one of the most tremendous eruptions recorded in history. The Islands of Jesso and Niphon, and Sumatra, contain more or less volcanoes; and from the Caspian sea, to the Azores is a volcanic range. Of Sicily and Italy, it is hardly necessary to speak in this enumeration, since the descriptions of Etna and Vesuvius; of Herculaneum and Pompeii, are well known, and are sufficient to indicate the volcanic disposition of that part of Europe. The West India Islands have occasionally suffered great calamities from this cause; and Iceland contains many burning mountains, among which is Skaptar Jokul, which in 1783, suffered an extraordinary eruption, which we shall describe.

The whole number of volcanoes known is about 200. See Von Hoff's Geology, vol. ii, and Lyell's Geology, vol. i. Article "Geography of Volcanic Regions."

General Characters and Geological Connections of Volcanoes. The forms of volcanic mountains are generally so peculiar as to be distinguished from all others. They are commonly of considerable height, and sometimes very lofty. When solitary they are of a conical form, and more or less truncated, that is, bearing the appearance of having been cut off at the top. When active, or but recently extinguished, the truncation has within it a cavity of greater or less size, called the crater.

The accurate form of a perfect crater is an inverted conoid, and on Cotopaxi and Teneriffe, they are surrounded by walls of lava, but most commonly this part is composed of ashes which have fallen down during eruptions. The size of the crater does not necessarily bear any proportion to that of the mountain. In some mountains both the size and shape varies with every eruption.

Proximity of Volcanoes to the Sea. In nearly all instances, volcanoes are seated near the sea, or in the vicinity of a large body of water, and it was formerly thought that proximity to the water, was absolutely necessary to their action; nor is it certain that this is not the case. The only exception to this general fact, is Jorullo, one of the burning mountains of the Andes, which is situated more than a hundred miles from the ocean, nor does it appear that any considerable body of water is near it. It has, however, been suggested, from some circumstances observed with respect to this mountain, that it may possibly communicate with the sea by a deep fissure. In many instances, volcanoes have thrown out mud or water, instead of lava, and ashes; and in some instances, fish of various kinds have been found in the water thus emitted, though no previous suspicion had existed, of a communication between the mountain and the sea.

VOLCANIC ERUPTIONS.

The action of most volcanoes is periodical, or intermitting, though this is not the case with all. Vesuvius

and Etna are sometimes dormant for a series of years, but Stromboli, in the vicinity of the former, has been constantly burning, ever since two hundred and ninety-two years before the Christian era, being upwards of two thousand years. Jorullo has continued to emit flames ever since 1759, at which time it was elevated from the plain on which it stands. But Vulcano suffered no eruption for eleven centuries, and we have already noticed that Ischia lay dormant for seventeen hundred years.

The appearances which attend volcanic eruptions, are various. In some instances, flames issue suddenly and silently from the cone, affording only splendid picturesque phenomena. But in others, the scene is the most terrific and appalling of which the imagination can conceive. For these descriptions we must, however, refer to particular eruptions, an account of which will follow.

The eruptions of Vesuvius and Etna, these mountains being in the midst of a highly cultivated people, are best described. Indeed, from the time of Pliny, to the present day, these have been the subjects of interesting and learned dissertations.

In general the first appearance of an eruption consists in a column of smoke rising to a great height, and then spreading out in the form which Pliny compared to that of a pine tree. This is followed by explosions from the craters; by trembling of the earth, or perhaps by its alternate rising and falling; the whole being attended by a rumbling, subterranean sound, forming both an eruption and an earthquake. Flame is then seen to issue from the cone, attended by red hot stones, often thrown to the height of several hundred feet, producing in the night, those brilliant and terrific phenomena, so often described. During the emission of the black smoke, and before the flame issues, there are often the most vivid flashes of lightning, which add greatly to the splendor of the scene. After these phenomena have existed for a longer or a shorter time, the melted lava, rising to the edge of the crater, flows over it, and runs down the side of the mountain into the plain below. This is in the form of a torrent of liquid fire, often narrow, but sometimes many miles in width. It sometimes proceeds rapidly, but more often slowly, the last portions of lava passing over the first, in small cascades. Sometimes, or from some mountains, there is much smoke, and but little lava; while from oth

ers, or at other times, the crater vomits rivers of melted matter, without smoke or flame.

The eruption of lava is often followed by showers of ashes, which consist of finely divided particles of lava, and which are often wafted by the wind, to the distance of several hundred miles.

The quantity of matter ejected by some volcanoes, is astonishingly great. Brieslak, an Italian geologist, calculated that the quantity of lava which flowed from a volcano in the island of Bourbon, in 1796, amounted to 45,000,000 of cubic feet; and that the quantity from the same, in 1787, was 60,000,000 of cubic feet; and during one eruption from a mountain in Iceland, the lava flowed about ninety miles, having a width of at least twenty miles, and in some places, a depth of several hundred feet.

PARTICULAR ERUPTIONS.

We shall describe a few volcanic eruptions, selecting only those which have been the subjects of peculiar, or scientific interest, or which have produced extraordinary effects, either with respect to the destruction they have caused, or the quantity of lava they have ejected.

Eruptions of Vesuvius. The most ancient eruption of this Italian mountain, of which there is any particular description, was in A. D. 79, at which time, the cities of Herculaneum and Pompeii were destroyed. It does not appear that any lava, or melted matter was emitted at this eruption; the ejected substances being sand, ashes and mud. But it is certain that this mountain had previously emitted lava, since the streets of these cities are paved with this substance. The first stream of lava, of which there is any account, was in 1036, being the sixth or seventh eruption on record. From this period, all the eruptions which have taken place, are recorded, and many of them described by scientific men, and at great length.

Some of them produced considerable changes, not only in the form and appearance of the mountain itself, but also of the country in the vicinity. That of 1538, elevated the land along the coast of Naples many feet, destroyed many villages, and produced Monte Nuovo, which is still

440 feet in height. A description and figure of this mountain will be given hereafter.

From about the end of the 18th century to 1822, the great crater of Vesuvius had been filling up gradually, with lava which boiled up from below, so that the bottom of the cavity presented a kind of rocky plain covered with blocks, crags, and hillocks of volcanic matter. But during the latter year, in the month of October, the form and appearance of the ancient crater was entirely changed. The explosions at that time were so violent during twenty days, as to break up, and throw out the whole of that accumulated mass, leaving an immense gulf, or chasm about three miles in circumference, and in some parts 2000 feet deep. At the same time about 800 feet in height, of the original cone or top of the ancient crater, was carried away by the explosions, so that Vesuvius became reduced in height from about 4200 to 3400 feet.-Forbes in Ed. Journal and Scrope in Jour. of Science.

In ascending this mountain, its sloping sides are found to be covered with loose materials intermixed with each other without the slightest order, and just as they fell from the crater. But on arriving at the crater itself, the beholder is surprised to find that every thing is there arranged in the most perfect symmetry, and that the materials are disposed in regular undulating strata. These consist of alternate layers, composed of lava, sand, ashes, and scoria, lying in distinct beds, and alternating with each other. These have resulted from the different colors, and coarseness of these materials, and which severally remain in the same situation and succession as they fell from the air during the different eruptions.

In some parts of the crater, are seen dykes, or veins of more compact matter intersecting the above described strata. These are on the outside of the cone, and being harder than the volcanic matter through which they have passed, they have resisted decomposition, and therefore project above the surface.

of

These have undoubtedly been formed by the filling up open fissures with liquid matter forced up from below. At what period they were formed is unknown, but if such fissures are formed by the cooling, and consequent shrinking of the crater, after an eruption, it is probable that at the next eruption, these are filled with the fused matter,