aceous lava and basalt, and poured them into the valleys; and beside the more ancient volcanoes, that have formed beds of basalt before the excavation of the valleys, there are other volcanic mountains, which have rounded summits or domes, without any perforation or crater, and these are chiefly composed of whitish or grey earthy felspar, containing imbedded crystals of felspar: to this rock the name of trachyte has been given, on account of its rough fracture. It may be properly called a volcanic porphyry.

The first, or more recent volcanoes, resemble in every particular the existing volcanoes in various parts of the world; and the currents of lava may be traced from their sides along the granitic plane on which the volcanoes stand, and thence into the adjacent valleys for many miles. The lava appears as fresh as the recent lavas from Vesuvius, though it has been exposed to the action of the atmosphere for some thousand years. The Puy de Pariou is the most perfect of these volcanic cones. The following description of it is taken from the 2d volume of my Travels:-" We were one hour in going from La Barraque, a mountain village, to the foot of the Puy de Pariou, where we left our char, and another hour in ascending to the summit, as we halted several times to rest. As nearly as I could estimate, the summit of this mountain rises about one thousand feet above the plain, and is therefore about three thousand eight hundred feet above the level of the The crater, which is the best preserved of any in Auvergne, is nearly circular. I walked round it, and its circumference is about eight hundred yards. Its shape is that of an inverted cone or funnel quite perfect. The edge or rim of the crater is narrow, from which the descent or slope is very rapid on each side: the depth of the crater from the highest part of the edge (which is on the southern side) to the small plain at the bottom, may be about three hundred and twenty feet; and from the western

sea.

side, about two hundred and sixty English feet. The lava which flowed from Pariou to La Barraque, and thence towards the plain of Clermont, is generally supposed to have issued from the crater; but had this been the case, the crater would not have been so entire as it is; and I am fully convinced, that the eruption of such a mass of lava must have broken down one of the sides, as at Nugere, which we afterwards visited, and the Puy de Vache. There appears, I think, decisive marks of the lava having flowed from an opening on the north-east side of the mountain, to which it may be traced. Indeed on this side there are the indications of a much larger crater, which has its escarpments turned towards the Puy de Pariou like those of Mount Somma, which are turned towards Vesuvius. The Puy de Pariou was, in all probability, a volcanic cone, formed within the larger crater by its last eruption of scoria.

"The annexed cut, from a drawing I made near the foot of the mountain, represents the external shape of the Puy de Pariou, and the dotted lines show the form and the relative depth of the crater, the bottom of which, a a, is about three hundred and twenty feet below the highest part of the rim c. The current of lava, b b, is on the north-east side of the present mountain. The internal shape of Pariou approaches to quadrilateral, or is that of a cone compressed on each side, and somewhat elongated from north to south. The bottom of the crater is nearly flat; there was a little water, from the recent melting of the snow, remaining in some of the hollows indeed we were told at Clermont that we should find the crater filled with snow. It was

early in May but the snow was gone, and grass was growing in some parts; others were covered with loose masses of scoriæ. Owing to the great porosity of the soil, the crater of Pariou seems doomed to perpetual sterility, there is no tree or shrub within it; while that of Vesuvius, after a cessation of erup

tions for only four centuries, was covered with large chestnut trees." Vol. ii. page 307.

In the Puy de Pariou, and many other volcanic mountains of this district, there is nothing particu larly remarkable, except, that the lavas which have flowed from them at a remote period, should preserve all the freshness of recent lavas, and that volcanoes so well characterised, both by their forms and mineral products, should have remained unnoticed until the middle of the last century. The round-topped or dome-shaped hill on the left of the Puy de Pariou is called Sarcoui; it belongs to that class of volcanoes that have no craters, which will subsequently be noticed. The more ancient vol canoes, that have poured out the thick beds of basalt that cap many of the valleys round Clermont, cannot always be traced, as the openings from whence it issued may be covered by the lava of more recent eruptions. In order to obtain a more distinct idea of the position of these caps of basalt, it will be necessary to remark, that the granitic plain above Clermont, and the hollows or valleys in its sides, received their present form prior to the most ancient volcanic eruptions; these hollows, or ancient valleys, were probably basins or lakes, in which were deposited a vast thickness of calcareous strata, containing freshwater shells, and the bones of land quadrupeds. Into these lakes, there has flowed a vast mass of volcanic tufa, covering the limestone, and sometimes intermixed with it. The volcanic tufa, and the freshwater strata, appear to have filled up the ancient valleys or lakes; and. on this tufa, the basalt was deposited by a subsequent eruption. At a later period, diluvial currents have. furrowed excavations or new valleys in the basalt, in the subjacent tufa, and in the freshwater limestone, leaving detached portions or hills, composed of basalt, tufa, and limestone, which once were parts of continuous beds. Into these new valleys, the lava of the most recent volcanoes has flowed. The most.

remarkable circumstance attending these more ancient eruptions, is the bituminous nature of the tufa, which forms the lowest bed, and covers the freshwater limestone of Gergovia, Canturges, and the neighbouring hills. This tufa is in some parts more than three hundred feet thick; it consists of earthy basalt or wacke, intermixed with lumps of scoriæ and basalt, and in some places with limestone: it is every where impregnated with bitumen. The tufa of Auvergne bears evident marks of being the product of an aqueous or muddy eruption, intermixed with lava and scoriæ, which increase in quantity in the upper part of the mass, and at length cover it with compact lava or basalt. That the tufa was ejected in an aqueous or muddy state is proved, by the quantity of bitumen which it contains: by any other mode of formation, the bitumen would have been consumed. By some former writers it has been supposed that the tufa is an alluvial bed of sediment and water-worn fragments; but the bituminous nature of this bed excludes the probability of this mode of formation; and at Montadoux, the upper part of the tufa may be clearly seen passing into basalt. In some situations, however, the tufa has been transported from its original situation, and intermixed with fragments of more ancient rocks.

The dome-shaped hills without craters, composed of volcanic porphyry or trachyte, have given rise to much speculation respecting their origin. Some geologists contend that they are only the remains of one vast bed of trachyte, of which the other parts are washed away. Others contend that they are merely portions of the granite on which they rest; and that this granite has been wholly or partially fused, and upheaved, by the expansive force of subterranean fire. This mode of formation is rendered probable, by what may be observed at the Puy de Chopine, which is a mountain standing within a crater; this mountain is partly composed of unaltered granite and sienite, and partly of vol

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