In the Mexican highlands a mutual dependence is p 240 also observed to exist among the volcanic mountains Orizaba, Popocatepel, Jorullo, and Colima; and I have shown* that they all lie in one direction between 18 degrees 59' and 19 degrees 12' north latitude, and are situated in a transverse fissure running from sea to sea.
[footnote] *Humboldt, 'Essai Politique sur la Nouv. Espagne', t. ii., p. 173-175.
The volcano of Jorullo broke forth on the 29th of September, 1759, exactly in this direction, and over the same transverse fissure, being elevated to a height of 1604 feet above the level of the surrounding plain. The mountain only once emitted an eruption of lava, in the same manner as is recorded of Mount Epomeo in Ischia, in the year 1302. But although Jorullo, which is eighty miles from any active volcano, is in the strict sense of the word a new mountain, it must not be compared with Monte Nuovo, near Puzzuolo, which first appeared on the 19th of September, 1538, and is rather to be classed among craters of elevation. I believe that I have furnished a more natural explanation of the eruption of the Mexican volcano, in comparing its appearance to the elevation of the Hill of Methone, now Methana, in the peninsula of Troezene. The description given by Strabo and Pausanias of this elevation, led one of the Roman poets, most celebrated for his richness of fancy, to develop views which agree in a remarkable manner with the theory of modern geognosy. "Near Troezene is a tumulus, steep and devoid of trees, once a plain, now a mountain. The vapors inclosed in dark caverns in vain seek a passage by which they may escape. The heavier earth, inflated by the force of the compressed vapors, expands like a bladder filled with air, or like a goat-skin. The ground has remained thus inflated, and the high projecting eminence has been solidified by time into a naked rock." Thus picturesquely, and, as analogous phenomena justify us in believing, thus truly has Ovid described that great natural phenomenon which occurred 282 years before our era, and consequently, 45 years bfore the volcanic separation of Thera (Santorino) and Therasia, between Troezene and Epidaurus, on the same spot where Russegger has found veins of trachyte.*
[footnote] *Ovid's description of the eruption of Methone ('Metam.', xv., p. 226-306): "Near Troezene stands a hill, exposed in air To winter winds, of leafy shadows bare: This once was level ground; but (strange to tell) Th' included vapors, that in caverns dwell, Laboring with colic pangs, and close confined, In vain sought issue for the rumbling wind: Yet still they heaved for vent, and heaving still, Enlarged the concave and shot up the hill, As breath extends a bladder, or the skins Of goats are blown t'inclose the hoarded wines; The mountain yet retains a mountain's face, And gathered rubbish heads the hollow space." 'Dryden's Translation'. [footnote continues] This description of a dome-shaped elevation on the continent is of great importance in a geognostical point of view, and coincides to a remarkable degree with Aristotle's account ('Meteor.', ii., 89, 17-19) of the upheaval of islands of eruption: "The heaving of the earth does not cease till the wind [(Greek word)] which occasions the shocks has made its escape into the crust of the earth. It is not long ago since this actually happened at Heraclea in Pontus, and a similar event formerly occurred at Hiera, one of the Aeolian Islands. A portion of the earth swelled up, and with loud noise rose into the form of a hill, till the mighty urging blast [(Greek word)] found an outlet, and ejected sparks and ashes which covered the neighborhood of Lipari, and even extended to several Italian cities." In this description, the vesicular distension of the earth's crust (a stage at which many trachytic mountains have remained) is very well distinguished from the eruption itself. Strabo, lib. i., p. 59 (Casaubon), likewise describes the phenomenon as it occurred at Methone: near the town, in the Bay of Hermione, there arose a flaming eruption; a fiery mountain, seven (?) stadia in height, was then thrown up, which during the day was inaccessible from its heat and sulphureous stench, but at night evolved an agreeable odor (?) , and was so hot that the sea boiled for a distance of five stadia, and was turbid for full twenty stadia, and also was filled with detached masses of rock. Regarding the present mineralogical character of the peninsula of Methana, see Fiedler, 'Reise durch Griechenland', th. i., s. 257-263.
p 241 Santorino is the most important of all the 'islands of eruption' belonging to volcanic chains.*
[footnote] *[I am indebted to the kindness of Professor E. Forbes for the following interesting account of the island of Santorino, and the adjacent islands of Neokaimeni and Microkaimeni. "The aspect of the bay is that of a great crater filled with water, Thera and Therasia forming its walls, and the other islands being after-productions in its center. We sounded with 250 fathoms of line in the middle of the bay, between Therasia and the main islands, but got no bottom. Both these islands appear to be similarly formed of successive strata of volcanic ashes, which, being of the most vivid and variegated colors, present a striking contrast to the black and cindery aspect of the central isles. Neokaimeni, the last-formed island, is a great heap of obsidian and scoriae. So, also, is the greater mass, Microkaimeni, which rises up in a conical form, and has a cavity or crater. On one side of this island, however, a section is exposed, and cliffs of fine pumiceous ash appear stratified in the greater islands. In the main island, the volcanic strata abut against the limestone mass of Mount St. Elias in such a way as to lead to the inference that they were deposited in a sea bottom in which the present mountain rose as a submarine mass of rock. The people at Santorino assured us that subterranean noises are not unfrequently heard, especially during calms and south winds, when they say the water of parts of the bay becomes the color of sulphur. My own impression is, that this group of islands, constitutes a crater of elevation, of which the outer ones are the remains of the walls, while the central group are of later origin, and consist partly of upheaved sea bottoms and partly of erupted matter — erupted, however, beneath the surface of the water.">[ — Tr.
It combines within itself p 242 the history of all islands of elevation. For upward of 2000 years, as far as history and tradition certify, it would appear as if nature were striving to form a volcano in the midst of the crater of elevation."*
[footnote] *Leop. von Buch, 'Physik. Beschr. der Canar. Inseln', s. 356-358, and particularly the French translation of this excellent work, p. 402; and his memoir in Poggendorf's 'Annalen', bd. xxxviii., s. 183. A submarine island has quite recently made its appearance within the crater of Santorino. In 1810 it was still fifteen fathoms below the surface of the sea, but in 1830 it had risen to within three or four. It rises steeply like a great cone, from the bottom of the sea, and the continuous activity of the submarine crater is obvious from the circumstance that sulphurous acid vapors are mixed with the sea water, in the eastern bay of Neokaimeni, in the same manner as at Vromolimni, near Methana. Coppered ships lie at anchor in the bay in order to get their bottoms cleaned and polished by this natural (volcanic) process. (Virlet, in the 'Bulletin de la Societe Geologique de France', t. iii., p. 109, and Fiedler 'Reise durch Griechenland', th. ii., s. 469 and 584.)
Similar insular elevations, and almost always at regular intervals of 80 or 90 years,* have been manifested in the island of St. Michael, in the Azores; but in this case the bottom of the sea has not been elevated at exactly the same parts.**
[footnote] *Appearance of a new island near St. Miguel, one of the Azores, 11th of June, 1638, 31st of December, 1719, 13th of June, 1811.