We

blackened country, where many forms of vegetation are blighted, grass is smothered and the trunks of trees don a dingy cloak. It is an artificial volcano on a small scale, with several craters, an attendant desert corresponding to that which surrounds Hecla, and a steady accumulation on the soil of the products of combustion. approach the cupola amid the deafening clank of trip-hammers and whir of fly-wheels in no feeble mimicry of the groans of the Titans under Ossa or Enceladus under Etna. The heat grows more and more oppressive as we draw toward the centre of activity. Presently, an opening is formed, and & white-hot torrent of slag, or lava, pours slowly forth. This cools so rapidly that the gases imprisoned within its substance have not time to escape. They thus give the hardened mass, generally, a cellular or porous structure and a comparatively low specific gravity. On the surface a crust forms immediately, and you may soon walk upon it without prejudice to your shoes, as the Vesuvian tourists traverse the still-moving lava and light their way with torches improvised by thrusting their walking-sticks into the crevices. Altogether, the rehearsal of the phenomena of an eruption is, as far as it goes, exact. It would be more so were a mound of earth and rock heaped up around the furnace

and its vent, while unlimited fuel continued to be supplied at the buried base. Dump into the chimney a quantity of material like that which surrounds it, add some barrels of water, and hurry out of the way. A violent ejection of lava in a vertical direction will take the place of the sluggish lateral flow we have witnessed. Cooled still more quickly by its more rapid passage through the atmosphere, it becomes more porous and lighter. It may resemble pumice. But there can be no such variety of mineral forms as that yielded by volcanoes. Lime, iron and clay, as a rule, comprise the contents of the furnace, with but a trifle of the characteristic element of sulphur, with which smelters of iron have as little to do as possible. The subterranean laboratory is infinite in its resources, and they appear in all the combinations heat can produce. The crystalline marble of the statuary, the granite of the builder, the gold-bearing quartz that enriches states, and the gem that glitters on the brow of beauty are but a few of the fruits of the same alembic. The lava itself varies greatly in the density of its structure, as, to a less extent, does its relative of the iron-furnace. Its gradations in this respect lie between basalt, or the almost equally hard paving-stones of Pompeii, and the delicate floating fibres scattered by Mauna Loa over the island at its base, and termed by the natives the hair of their ancient goddess Pelé. The latter substance is the result of a current of cold air passing sharply across the surface of an outpour of lava, and has been recently reproduced artificially

It

at the great iron-works of Essen. resembles spun glass, and may, like it, be used as a textile. Pumice, which is lighter than water, and in great eruptions has been known to cover square miles of sea, is a more familiar form.

Man has naturally been always curious about the chimneys of his spherical dwelling-place. He is fond of observing them from below, and, when he can, from above. Vesuvius is one of the stock shows of Italy, like the Apollo and the Coliseum. Two generations ago 'its blaze' was a usual sight to gaping tourists from its hackneyed height.' It is still more so now, the telegraph enabling lovers of the marvellous to stay at home till the last moment, and traverse Europe between the last preliminary throe and the actual outbreak. After the construction of a few more railways on the west coast of South America we shall, on our side of the Atlantic, be able to make pleasure excursions at short notice to Sangay, Sorata and Antuco, each of which in round numbers exceed in altitude by fifty percent, Vesuvius piled on Etna.

Free from danger, seated in a region where the fire-mountain and the mastodon seem equally extinct, let us take a peep into these fiery secrets of the under-world. We have the advantage over the jackdaw studying the hole in the millstone, in that our view is not met by utter darkness. We climb, for example, with Spallanzani and his successors to the top of Stromboli. A third of the way down the mountainside, opposite to that by which we ascended, we see the bowl of white-hot broth that has been full and bubbling without the slightest intermission for at least twenty-three centuries. At intervals more or less regular it boils over with a splutter that shakes the earth and sends a spray of incandes cent rocks into the sea, which grumbles the while like a blacksmith's waterbarrel when he cools a bar of iron from the anvil. Or, turning our backs on this very moderate specimen of a volcanic vent, we step to the Sandwich Islands and skirt the six square miles of molten lava at Kilauea, the lower and secondary crater of Mauna Loa. It would melt down two Strombolis, and the five hundred feet through

which it rises and falls would scarce be so increased, by the throwing of them into the basin, as to cause the overflow which has long been looked for in vain. Vaster still, though not at present occupied by lava, is the cavity of Dasar in Java. Standing on its brim, three hundred feet high, one can scarcely perceive a horseman in the middle, and to traverse its utterly barren expanse, deep with cinders, is a fatiguing march. There are, moreover, craters within craters, like a cup and saucer, the cup reversed and a hole in its bottom. This is a common form, the interior cone being composed of the later ejections, and changing shape and dimensions with

the fluctuations in the activity of the volcano. Etna and Vesuvius vary their profile in a course of years by the growth and decrease of this mound. It sometimes rises several hundred feet above the level of the wall of the main crater, and its disappearance correspondingly reduces the apparent height of the mountain.

The size of the crater does not bear any fixed relation to that of the volcano to which it belongs. The diameter of the summit-basin of Volcano, one of the Lipari Islands, which has the hon our of having contributed the generic name, is, for instance, three thousand feet, the mountain rising but twelve hundred feet above the sea; while

moments of frenzy, and branch off, like some human spouters, into sideissues, but there are volcanoes devoid of terminal craters altogether. Among those is Antisana, nineteen thousand feet high. Nor can Ararat be said to possess one. This famous hill, 17,210 feet above the sea and 14,000 above the surrounding plain, only took its place in the ranks of active volcanoes in 1840, after a silence running back beyond the event which gives it celebrity. The eruption of that year is unfortunately less minutely chronicled than the voyage of the ark, but it ap

pears to have proceeded from an opening in the flank of the mountain.

As water is so important an agent in the production of volcanic throes, it is looked to by those who have an immediate and fearful interest in the matter to give warning of an approaching convulsion. The wells, they say, sink and the springs disappear, as the departure of the savages from the vicinity of the settlements used to betoken to our frontiers-men an Indian war. The element, so powerful as a friend and an enemy, begins its attack by drawing in its pickets. The time

for preparation may be a few hours or it may be some days, but when the wells change level it has come. So it was at Naples in 1779, 1806 and 1822. At the same time, the sign is not infallible, nor does it always manifest itself when an eruption is at hand. A cause for the frequent occurrence of the phenomenon is easy to suggest. The expulsion of an enormous volume of matter, solid or gaseous, must pro

duce a vacuum, and any surface fluid within reach will be absorbed to fill it. An infusion of the water with clay, scoriæ or other matter by the direct action of the expulsive force, changing its colour to white, red or black, admits of as ready an explanation. When such portents are followed closely by a preliminary growl from the awakening monster, the crisis cannot be far off. The move

MOUNT BOURBON.