layers of flint passing into semi-opal, especially in the vicinity of volcanic rocks. At St. Pierre Eynac these siliceous strata evidently pass under the powerful clinkstone mass of Montplaux. Towards the middle of the basin the clayey marls alternate with beds of gypsum, several of which are sufficiently rich to be worked for agricultural and other uses. The shells contained in these beds are of lacustrine or marshy species; bones also occur in them, and the remains of fish, crustacea, birds, and their eggs." Above the marls with gypsum is usually a considerable thickness of calcareous and foliated marly strata, alternating with greyish limestone of the consistence of chalk, having tubular cavities attesting its palustrine origin, and numerous casts of planorbes, limnei, cyclostomæ, bulimi, cyprides, &c. Bones and teeth of animals, both terrestrial and aquatic, are also found in them abundantly, for a catalogue of which I must refer to M.Pomel.† In one site alone, the hill of Ronzon, and nearly in one bed, so large a number and variety of organic remains occur as almost to furnish a complete Fauna of the district at the period of its deposition, which MM. Pomel, Aymard, and Lyell unite in referring to the Lower Miocene.

There is no clear evidence of the outburst of any neighbouring volcanos during the tertiary period in which these sedimentary beds were deposited in the freshwater lake of the Haute Loire. No alternation of volcanic matters with the sedimentary strata, such as those already described in the Limagne, have been detected within this basin. It is possible, therefore, that the earliest development of local volcanos occasioned such a disturbance as to cause the drainage of the lake; on the other hand, several of the basaltic breccias, which we shall have occa

* M. Aymard mentions the following mammifers, as found by him in these beds:-Palæotherium primævum, Pal, sub

gracile, Monacrum velaunum.
+ See Appendix.

sion to describe among the volcanic rocks of this district, bear a near resemblance to the peperino of the Auvergne lake-basin, and were perhaps, like that rock, the product of eruptions from within its area before the waters were wholly drawn off.

IV. BASIN OF MONTBRISON.

I have not myself visited this locality, nor am I acquainted with any detailed description of it. It occupies a valley-plain, about 20 miles long by 10 in width, encased between the granite and gneiss ranges of the Forèz and the Lyonnais on the south, west, and east, and the porphyry rocks and Devonian strata of the Tarare, through which the Loire finds an outlet to the north. The tertiary strata of this basin have so close a resemblance in character and position with those of the lower valley of the same river about Roanne, as to lead M. Raulin to presume that the two basins were originally connected by a channel permitting their waters to maintain the same level. The same red and yellow sands, sandstones, clays, and green and white foliated marls are found at Marcilly, Boën, Sury le Comtal, and generally throughout the plain. Several eruptions of volcanic matter appear also to have taken place within this basin, and from the granitic heights to the west. But for the reason given above I am not aware of the precise circumstances under which the volcanic rocks present themselves. M. le Coq informs me that several basaltic dykes appear near the junction of the porphyry and granite; while others penetrate through beds of rolled pebbles, probably belonging to the lower term of the lacustrine series. A further examination of this basin seems very desirable.

V. TRIPOLI BASIN OF MENAT.

At Menat, on the road from Riom to Montaigu, occurs a sin

* Bulletin XIV. p. 584.

gular depression in the gneiss and mica-schist which here take the place of the granite of the primary or crystalline platform. It is nearly circular and about a mile in diameter, and discharges its waters into the Sioule through a narrow gulley worn in the schists not more than 12 feet wide and as many deep. Before this passage was effected they must have formed a lake over the whole valley, the surface of which is almost perfectly level.

The excavations that have been made in the sedimentary beds beneath this surface show them to be composed to a considerable but unascertained depth of bituminous shale, or desiccated flaky clay of a muddy black colour, evidently the fine detritus of the micaceous and talcose rocks which enclose the basin impregnated with bituminous matter, and often containing vegetable remains in such abundance as to become a true lignite. It envelops many nodules of iron pyrites, globular or lenticular, sometimes assuming the flattened moulds of fish, chiefly a cyprinus, very like the Cyp. papyraceus of the lignite of the Siebengebirge. The thin folia of the shale and lignite exhibit on their surface innumerable impressions of leaves resembling those of the chesnut, sycamore, willow, lime, and aspen, which still grow in the neighbourhood, with others which certainly do not belong to European species, and resemble those of the liquid amber, Styraciflua and Gossypium arboreum.* Some flattened fruit, or seed-vessels, are also found resembling those of the hornbeam. These lignites appear to have undergone spontaneous combustion on some points (probably where pyrites abounded), and the shale has been thus converted into reddish tripoli, which is largely quarried for commercial use. It seems probable that the formation of this simple alluvial deposit is of no very distant date.

Bouillet, 'Vues et Coupes du Puy de Dôme.'

CHAPTER III.

INTRODUCTORY ACCOUNT OF THE NOTICES WHICH HAVE BEEN HITHERTO PUBLISHED CONCERNING THE VOLCANIC REMAINS OF THE INTERIOR OF FRANCE.

To those who now travel over the mountains of central France, and see on all sides marks of volcanic agency exhibited in the most decided manner, numerous hills formed entirely of loose cinders, red, porous, and scorified as those just thrown from a furnace, and surrounded by plains of black and rugged lava, on which the lichen almost refuses to vegetate, it appears scarcely credible that, previous to the middle of the last century, no one had thought of attributing these marks of desolation to the only power in nature capable of producing them. This apparent blindness is however very natural, and not without example. The inhabitants of Herculaneum and Pompeia built their houses with the lavas of Vesuvius, ploughed up its scoriæ and ashes, and gathered their chesnuts from its crater, without dreaming of their neighbourhood to a volcano which was to give the first notice of its existence by burying them under the products of its eruptions. The Catanians regarded as fables all relations of the former activity of Etna, when, in 1669, half their town was overwhelmed by one of its currents of lava.

In the year 1751 two members of the Academy of Paris, Guettard and Malesherbes, on their return from Italy, where they had visited Vesuvius and observed its productions, passed through Montelimart, a small town on the left bank of the Rhône, and, after dining with a party of savans resident there,

amongst whom was M. Faujas de St. Fond, walked out to explore the neighbourhood. The pavement of the streets immediately attracted their attention. It is formed of short articulations of basaltic columns planted perpendicularly in the ground, and resembles in consequence those ancient roads in the vicinity of Rome, which are paved with polygonal slabs of lava. Upon inquiry they learnt that these stones were brought from the rock upon which the Castle of Rochemaure is built, on the opposite side of the Rhône; and were informed, moreover, that the mountains of the Vivarais abounded with similar rocks. This account determined the Academicians to visit that province, and step by step they reached the capital of Auvergne, discovering every day fresh reason to believe in the volcanic nature of the mountains they traversed. Here all doubts on the subject ceased. The currents of lava in the vicinity of Clermont, black and rugged as those of Vesuvius, descending uninterruptedly from some conical hills of scoriæ, most of which present a regular crater, convinced them of the truth of their conjectures, and they loudly proclaimed the interesting discovery.

On their return to Paris M. Guettard published a Memoir announcing the existence of volcanic remains in Auvergne,* but obtained very little credit. The idea appeared to most persons an extravagance; and even at Clermont a sagacious professor, who ascribed the volcanic scoria to the remains of iron-furnaces established in the neighbouring mountains by those authors of everything marvellous, the Romans, gained far more partisans than the naturalist. By degrees, however, the obstinacy of ignorance was forced to yield to conviction, and M. Desmarest some years afterwards, having published his Memoirs on the

Mémoire sur quelques Montagnes de la France qui ont été des Volcans.Mém, de l'Acad. des Sciences, 1752.