crust or covering over the incandescent mass beneath. The lava of Kirauea appears to be similar to that of Hecla, which is known under the name 'cavernous;' and which, by the intensity of its heat, and the abundance of its elastic gases, produces here, as in Iceland, tumefactions, varying from the thickness and delicacy of a soap-bubble, to the size of caverns twenty or thirty feet wide. These caverns, which extend in every direction, form, beneath the surface of the island, subterranean channels, though which the overflowing lava makes its way, and are often covered by a hollow arch, which yields at once to the tread. Their interior contains the most interesting incrustations of sublimed minerals, with crystalline forms, the perfection of which can hardly be appreciated without the aid of a microscope, and so delicate as scarcely to bear the breath. Mounds of sulphur, more extensive than those of Solfatara, are deposited around the southern plane of the crater.

"On the western flank of the crater above described, the appearances render it probable that the former surface of the incandescent matter was 300 feet higher up than it is at present; and that the opening of the crater of Mauna Roa, which is now 8000 feet above, diverted the course of the intense subterranean heat from that of Kirauea, or at least diminished its intensity. It seems, also, that the incandescent matter of the interior of the crater became refrigerated and solidified in the mighty cauldron; and that after a lapse of time the base on which it stood gave way, under the renewed agency of subterranean heat, when the mass cracked and slipped. A large mass of the solidified lava appears to have fallen again into the abyss, and been remolten: while a part remained lodged against the sides of the cauldron, and is now seen as a rock two hundred feet high, consisting of basalt, trachyte, and lava of several varieties. Between the scoriaceous lava approaching to slag, which lies uppermost, and the close-grained basalt which forms the lowest portion of the rock, the transition is so gradual, that it is impossible to assign the spot where basalt ceases and lava begins. The words, basalt, trachyte, and lava serve, therefore, only to distinguish the upper from the lower part of a stream of molten matter."

18. THE VOLCANO OF JORULLO.-In South America volcanic action has been, and is still, exerted over an immense extent of country; and the vents of the subterranean fires extend to the loftiest summits of the Andes.

In the parallel of the city of Mexico there are no less than five burning mountains-Tuxtla, Orizaba, Popocatepetl, Jorullo, and Colima-arranged as if they originated in an

immense fissure, traversing the region from east to west, and extending from sea to sea.

The elevated country which constitutes the province of Quito is, as it were, an arch or dome, spread over an immense focus of volcanic energy, of which the channels of communication with the atmosphere are the burning mountains of Pichincha, Cotopaxi, and Tunguragua. These, by their grouping, as well as by their lofty elevation and grand outline, present the most sublime and picturesque aspect which is anywhere concentrated within so small a space in volcanic landscape.

LIGN. 201-VOLCANO OF JORULLO, AND ITS HORNITOS, MEXICU.

(As seen by Baron Humboldt, about 1800.)

Eruption of Jorullo.-South America has been the theatre, in modern times, of one of the most extraordinary revolutions in the annals of the physical history of our planet,that which gave rise to the burning mountain of Jorullo.*

* Baron Humboldt's "Nouvelle Espagne;" see also his "Vues des Cordillères," for beautiful illustrations of Jorullo and its hornitos.

In Mexico there is an extensive plain called the Malpays, which was covered by fields of cotton, sugar-cane, and indigo, irrigated by streams, and bounded by basaltic mountains, the nearest active volcano being at the distance of eighty miles. This district is situated at an elevation of about 2600 feet above the level of the sea, and was celebrated for its beauty and extreme fertility. In June, 1759, alarming subterranean sounds were heard, and these were accompanied by frequent earthquakes, which were succeeded by others for several weeks, to the great consternation of the neighbouring inhabitants. In September tranquillity appeared to be reëstablished, when in the night of the 28th the subterranean noise was again heard, and part of the plain of the Malpays,* from three to four miles in extent, rose up like a mass of viscid fluid, in the shape of a bladder or dome, to a height of nearly 1700 feet; flames issued forth, fragments of red-hot stones were thrown to prodigious heights, and through a thick cloud of ashes, illumined by volcanic fire, the softened surface of the earth was seen to swell up like an agitated sea. A huge cone, above 500 feet high, with five smaller conical mounds, suddenly appeared, and thousands of lesser cones (called by the natives hornitos, or ovens) issued forth from the upraised plain (Lign. 201). These consist of clay intermingled with decomposed basalt, each cone being a fumarole, or gaseous vent, from which issued thick vapour. The central cone of Jorullo is still burning, and on one side has thrown up an immense quantity of scorified and basaltic lavas, containing fragments of old crystalline rocks. Two streams, of the temperature of 186° of Fahrenheit, have since burst through the argillaceous

-Cosmos, Bohn's Edit. vol. i. p. 227, note. Burckhardt states, that during the twenty-four years subsequent to Baron Humboldt's visit to Lurullo, the hornitos had either wholly disappeared or completely changed their form.-Reisen in Mexico, &c.

* The tract consisted of porphyritic rocks.

vault of the hornitos, and now flow into the neighbouring plains. For many years after the first eruption, the plains of Jorullo were uninhabitable from the intense heat that prevailed.

19. SUBMARINE VOLCANOS.-Volcanic eruptions take place indiscriminately either on the land or beneath the waters of the ocean. The igneous foci of Southern Italy are certainly not confined to the land, but extend beneath the bed of the Mediterranean; and of this the occasional appearance of new shoals and islands affords conclusive evidence. Livy informs us that an event of this kind, which took place about the period of the death of Hannibal, together with other volcanic phenomena, so terrified the Roman people, as to induce them to decree a supplication to the gods, to avert the displeasure of heaven, which these prodigies were supposed to denote. "Nuntiatumque erat haud procul Siciliâ insulam quæ nunquam ante fuerat novam editam e mari esse."-LIVY, lib. xxxix. c. 56.

In Iceland, which may be regarded as a partially submarine volcanic mountain, with the highest summits above the waters, eruptions are not restricted to the area of dry land; but often burst out in submarine volcanos off the coasts. The enormous eruptions which issued from three different vents in the low tract called Shaptar Jokul, in 1783, and poured out lava-currents many miles wide, and ninety long, was preceded by the appearance of volcanic cones, vomiting flames and vapour, in the neighbouring sea, many miles from the land.*

A highly interesting example of the emergence of a submarine volcano took place in 1831. A volcanic island suddenly arose in the Mediterranean, about thirty miles off the S.W. coast of Sicily, where previous soundings had ascertained the depth of the sea to be 600 feet. It was preceded

"Travels in the Island of Iceland, during the Summer of the year 1810." By Sir George Stewart Mackenzie, Baronet, 4to, 1811.

by a violent spouting up of steam and water, and at length. a small island gradually appeared, having a crater on its summit, which ejected scoriæ, ashes, and volumes of vapour; the sea around was covered with floating cinders and shoals of dead fishes. The crater attained an elevation of nearly 200 feet, with a circumference of about three miles, having a circular basin full of boiling water of a dingy red colour. It continued in activity for three weeks, and then gradually disappeared. The island received various names; but it is best known by the English name of "Graham's Island," and the French one of "l'Isle Julia." In 1833, two years after

LIGN. 202.-VOLCANIC ISLAND THROWN UP IN THE MEDITERRANEAN IN 1831.

its destruction, a dangerous reef remained, eleven feet under the water; in the centre of which was a black volcanic rock (probably the remains of the solid lava ejected during the eruption), surrounded by shoals of scoria and sand. The appearance of the island, when visited by M. Constant Prévost, is shown in this sketch (Lign. 202), from a draw

See his "Rapport sur le Voyage à l'Ile Julia en 1831 et 1832." Also Annales des Sc. Nat. 1831, vol. xxiv. p. 103.