ANCIENT VOLCANOES OF AUVERGNE.

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issuing from conical chimnies, are merely the expiring fumes of those furnaces, that have once desolated whole regions of the earth. Of this fact, we have convincing evidence in France, which has never been visited by volcanic fire, within the memory of man; yet there is no country where volcanic products exist in greater variety, in closer affinity with one another, or in more interesting forms, than in the heart of that kingdom. Travelling in that territory from the north, the first volcanic lavas occur in Auvergne, to the west of Clermont, on the granite table-land bounded by the rivers Allier and Sionle. Extinct volcanoes, to the number of 100 appear in an immense range of insulated conical hills about 700 feet in height, formed of masses of solid lava, and spongy scoriæ. Their tops are hollowed out in the crater form, the edges of the cup being in many cases entire and well defined. The streams of lava are blistery on the surface, and bristling with scoriform asperities, which rise sometimes three feet high. The deeper we penetrate into the mass, it becomes less cellular and more compact, exactly as in modern lava streams; yet the basis occasionally differs in no respect from that of the finer basaltic prisms, including like it, grains or crystals of augite, olivine, and felspar. The lavas have sometimes spread widely over the plains, and at others flowed into narrow valleys, following their windings through a distance of 9 or 10 miles. In their progress, they have obviously taken the lowest track, bending over or gliding about, the rising grounds which obstructed their advance, and like every stream of liquid mat

ter, have observed strictly the laws of hydrostatics. The natural history of these lavas is therefore complete, and needs no aid of fancy to identify their volcanic source; for we perceive the focus that poured them out, the path they percurred, the obstacles they shunned, and the strata which they overwhelmed and still cover.

In the same district, there also occur genuine basalts, or submarine lavas of more ancient date, being anterior to the excavation of the valleys, while the lava streams are evidently posterior to this event. The basalts appear under the form of horizontal coulees, or sheets, covering portions of elevated land since upheaved, or constituting the caps of mountain chains and insulated peaks. These are shreds of antediluvian and diluvian lavas.

In Velay and Vivarais volcanic lava forms a great portion of the surface of the ground, exhibiting in certain spots, interesting phenomena. Near Montpesat, Thueys, and Jaujac, small extinct volcanic hills are still to be observed; and a stream of lava may be traced from the foot of each, running down the valleys. The shape of these currents is perfectly defined. Their bottom reposes on a stratum of pebbly gravel, and is altogether scoriform; while higher up the lava is split into most regular prisms, as sonorous as metallic iron, and in beautiful colonnades. The basis of the lava is black coloured and compact, containing grains of olivine and augite. It has flowed evidently after the excavation of the valleys. Similar appearances pervade the south of France down to the Mediterranean shores. Near Agde, the extinct volcano of St. Loup occurs,

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composed of cellular lavas; which have been employed in the hydraulic architecture of the canal of Languedoc.

The volcanic remains of central France have been recently illustrated by two ingenious practical geologists, Dr. Daubeny and Mr. Scrope; from the latter of whom I shall select a few facts, as they have been well arranged in the Quarterly Review for October 1827. The associated rocks of igneous origin seem scarcely in any instance to have been repeated in the same spot, but to have burst forth singly and successively on different though neighbouring points, remarkable for their general distribution in a line from North to South; a direction coincident with that of the granitic beds, from whose interior they have apparently, burst forth. To the west of the valley of the Limagne, immediately behind Clermont, rises a granitic plateau, about 1600 feet above the valley, and 3000 above the sea. On this rests a chain of volcanic hills about 70 in number, composed of steep truncated cones, called the Puys of the Monts Dome, which form with the ashes and scoriæ scattered around, an irregular ridge, from 500 to 1000 feet high, and about 18 miles in length by 2 in breadth. They consist of loose scoriæ, blocks of lava, lapillo, and puzzolana, with fragments of trachyte, and granite. The

Trachyte is a volcanic rock, characterised by its porphyritic structure; its scorified and cellular aspect; its harsh feel (whence its name rough-stone); and by the imbedded crystals of glassy felspar. These minerals are sometimes impasted in a felspathic light coloured cement. It is a rock entirely absent in the British islands; but the clay porphyry associated with red sandstone in the island of Arran, and that of Sandy

lava-currents, traceable to the craters of these cones, present the image of a black and stormy sea of viscid matter, suddenly congealed at the moment of its wildest agitation.

One of the largest volcanic cones of the district, the Petit Puy de Dome, has a very regular crater 300 feet in width and depth, elevated more than four thousand feet above the level of the sea. It consists entirely of fragmentary matter, basaltic scoriæ, sand and ashes. The Puy de Louchadière is the most striking of the chain. Completely insulated from the others, it rises at an angle of 35°, in a majestic cone to the height of more than 1000 feet from the western plain, forming a total elevation of 3956 feet.

Mont Dor is a mountainous tract, the higher portion of which is divided into seven or eight rocky summits, grouped together within a circuit of about a mile in diameter, the highest rising to 6217 feet above the level of the sea. The whole of this mass consists of successive beds of volcanic origin, and of immense thickness, which almost conceal the primitive soil.

The currents of basalt have flowed on all sides to the distance of fifteen, twenty, and in some instances twenty-five or thirty miles from the central heights. The plateaur of trachyte on the contrary, rarely extend beyond a circle of ten miles radius ; but what the latter currents want in length, they possess in height and breadth.

In the ancient province of Velay, Mr. Scrope

Brae presents numerous analogies. Some modern lavas of Vesuvius approach very nearly in composition and appearance to trachyte, and the oldest volcanic products on Ætna and Teneriffe are composed of it.

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counted more than a hundred and fifty cones, so thickly sown along the axis of the granitic range, that separates the Loire and Allier from Palhaguet to Pradelle, as generally to touch each other by their bases, and thus to form an almost continuous chain.

Germany, particularly on the banks of the Rhine, in Hessia, Saxony and Bohemia, presents a great many remains of basaltic lava-streams, accompanied often with clinkstones, in mountain groups. some localities, volcanic tufas, with cellular and scoriform lavas occur.

In

It is hardly necessary to say that Sicily and Italy particularly in the Vicentin, the environs of Rome, and Naples, include extensive volcanic formations. No less than 60 ancient craters have been specified in a small tract of Italy. When these were active, what a frightful region must it have been !

There are at present 205 burning volcanoes on the globe. 107 of these occur in islands, and 98 on continents, but ranged mostly along their shores. The American volcanoes are among those most distant from the sea. In Peru, they are about 70 miles from it. The volcano Popocatepec is 140 miles inland, but it merely smokes.

We owe to missionary zeal, an acquaintance with the most remarkable volcano ever described, in the island of Owhyhee, where several exist in an active state.

Mouna Roa, a mountain of trachytic formation estimated to rise to the prodigious height of 15000 feet, contains an enormous crater, 8 miles in circumference, and includes a vast lake of molten lava, subject to horrific explosions and undulations.