COMPOSITION OF LAVAS.

of olivine, pyroxene, and obsidian.*

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And the furrows

* Milner, in The Gallery of Nature, says that lava is chiefly composed of the two minerals feldspar and augite, with titaniferous iron. When the feldspar predominates, light-colored lavas are the result, called feldspatnic or trachytic; but when the augite is in excess, dark varieties, augitic or basaltic lavas, are produced. Other simple minerals occur, but in very inconsiderable proportions. (Humboldt says that he found five metals among the products of existing volcanoesiron, copper, lead, arsenic, and selenium, in the crater of one volcano. ) Besides varying in chemical composition, the character of lava is greatly modified by the circumstances under which it is cooled down, compact rock resulting from cooling under pressure, but a porous, fibrous, and light material being produced when cooled with the sole weight of the atmosphere upon it. If we suppose a current of matter of the consistency of honey, we shall have a tolerably correct picture of a stream of lava, which, as it moves over a district, is not thinned, but walled at the sides, and, a crust soon forming upon the surface, tends still more to prevent it spreading out laterally. Hence it is sometimes possible, when the ground favors the attempt, to deflect one of these fiery floods from its course by attacking the sides, and removing the crust, which has succeeded in turning it away from towns that have been threatened by it. In one instance the inhabitants of Catania assailed a lava current in this way, to divert it from their city, when the people of another locality, who were placed in jeopardy, took up arms to resist the operation.

Lava rapidly cools externally, but the crust formed being a bad conductor of heat, the interior of the mass remains hot, semi-fluid, and moves on after the surface has solidified. The stream thrown out of Ætna in 1819 was in motion, at the rate of a yard per day, nine months after the eruption; and another from the same mountain is stated not to have become completely consolidated and at rest ten years after its emission. Dr. Daubeny states, speaking of temperature, that some days after ejection lava has raised the thermometer from fifty-nine to ninety-five degrees at the distance of twelve feet, while three feet off the heat greatly exceeded that of boiling water; that it has rendered a mass of lead fluid in four minutes, when the same mass, placed on red-hot iron, would have required double that time to enter into fusion; and that even stones have been melted when thrown into the lavas of Etna and Vesuvius.

Obsidian, another volcanic product, is a black, glassy lava, contain ing a large proportion of silica, named, according to Pliny, after its

between the swells and petrified waves are filled with the same, or with a light spumous lava, like the froth of the sea drifted by the wind.

Across this fire-frozen sea, like a vast Alpine glacier, there runs a high, ragged ridge, burst up and broken, no one can tell how, till it is jagged as a millsaw, which you can no more get over, or get round it, than you can scale one of those high walls which are sometimes to be seen at fortified places and elsewhere, thickly planted and bristling all over with sharp pieces of junk bottle. Being ahead of our guides, we lost our way there, and wandered some time in that

Dreary plain, forlorn and wild,

The seat of desolation,

like that which offered rest to Satan's feet,

From off the tossing of the fiery waves.

Once we came suddenly upon a tall, oven-like cone, so much like a sentry-box, that, with Milton's description in mind of the place

Eternal Justice has prepared for those rebellious,

you might almost look to see some sentinel fiend come out from it, and hail you gruffly, "Who goes there?"

At length, by retracing all our steps, we got out of this dreary domain into the traveled tract, and made for the volcano, whose sulphurous smoke and stench

first observer, Obsidius. Scoriæ, cinders, ashes, and stones are identical, in mineral composition, with the lava currents, and are portions of them, abstracted while yet in the fiery funnel, and shot upward by the explosive energies in operation.

SKIRTS OF THE Ꮯ Ꭱ Ꭺ Ꭲ Ꭼ Ꭱ.

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we now began to perceive driven along by the trade wind, and to see the vitreous threads of Pele's hair, caught in crevices and cobwebs, and shining in the sun with a metallic lustre. As you proceed, the lava is more decomposed, and the ground cracked and rent into fissures and chasms, from which there is issuing steam and vapor of smoke, and you seem to be in a region of lime-kilns or smelting-furnaces. A mile or two further on you descend two or three hundred feet, on to a vast terrace-like, sunken plain, rent here and there by earthquakes, and strewed with great boulders of lava, and sounding unsafe and hollow under the tramp of your horse, who begins to show his consciousness of a dangerous proximity to the great laboratory of nature, to which this is the vast outer court and hall of entrance.

By the time you reach the skirts of this sunken plain you begin to get an idea of the unique Hawaiian volcano; not like the pictures we have of other volcanoes, the truncated top of a mountain with a broad base and furrowed sides made by the overflow and hardening of its lava, and its summit distinguishable at a distance as the raised brim of a mighty cal dron, but an immense gaping chasm, or hideous fireeaten pit, variously estimated from nine to fifteen hundred feet deep, and from nine to fifteen miles in circumference.

The scientific Pole, Count Strezelecki, thus roughly sketched the results of his observations for a friend, in the Hawaiian Spectator: "What I remember, and long shall recollect, as showing the mighty influence of mighty objects upon me, are the difficulties I had

to struggle with before my eye could be torn away from the idle, vacant, but ecstatic gazing with which I regarded the great WHOLE, down to the analytical part of the wondrous and unparalleled scene before me-I say unparalleled, because, having visited most of the European and American volcanoes, I find the greatest of them inferior to Kilauea in intensity, grandeur, and extent or area.

"The abrupt and precipitous cliff which forms the north-northeast wall of the crater, found, after my repeated observations, to be elevated four thousand one hundred and four feet above the level of the sea, overhangs an area of three million one hundred and fifty thousand square yards of half-cooled scoria, sunk to the depth of three hundred yards, and containing more than three hundred and twenty-eight thousand square yards of convulsed torrents of earths in igneous fusion, and gaseous fluids constantly effervescing, boiling, spouting, rolling in all directions like waves of a disturbed sea, violently beating the edge of the caldrons like an infuriated surf, and, like surf, spreading all around its spray in the form of capillary glass, which fills the air, and adheres in a flaky and pendulous form to the distorted and broken masses of the lava all around; five caldrons, each of about five thousand seven hundred square yards, almost at the level of the great area, and containing only the twelfth part of the red liquid.

"The sixth caldron is encircled by a wall of accumulated scoria of fifty yards high, forming the southsouthwest point; the Hale mau mau, to which the bones of the former high chiefs were consigned, the