1. The lowest visible beds consist of a compact brownish grey limestone containing much fragmentary volcanic matter, generally arranged as above described in each stratum according to their respective gravities, the largest fragments at the bottom, the rest diminishing in size in proportion to their distance from thence. These beds dip rapidly below the level of the river, and are covered by

2. A bed about 4 feet thick of a coarse-grained limestone of an ochreous yellow colour and earthy fracture, without any visible admixture of volcanic matter. It contains the casts of numerous shells, Planorbes, Helices, Lymnei, the shells being often replaced by bitumen, which exudes likewise from fissures in the rock. This is a very common variety of the hard limestone beds frequent throughout the lacustrine series.

3. Above this is a considerable thickness of the soft white foliated marly limestone, characteristic of the formation, having a plain fracture, sometimes slightly conchoidal, strongly adhering to the tongue, with an earthy smell, its exposed surfaces occasionally presenting efflorescent carbonate of soda. It has frequently a tendency to desquamate in globular masses.

4. A single bed, 10 inches thick, of a very compact, hard, and fine-grained limestone, with a conchoidal fracture, of a deep bluish-black, probably coloured by volcanic ashes.

5. Numerous calcareo-volcanic strata, similar to No. 1; some of them being ribboned with different colours, yellow, brown, or bluish-black, determined, it seems, by the greater or less proportion of volcanic ashes contained in their several zones. Where this proportion is considerable the rock generally has the more compact character and conchoidal fracture; and by still further increase of the volcanic element it passes into a kind of peperino or basaltic breccia, which often affects a globular concretionary structure.

The strata interspersed with volcanic matter are perfectly parallel to those that are free from it, and present all the characters that we should expect in sediment slowly and tranquilly deposited in a body of water into which repeated showers of volcanic ashes and fragments were occasionally ejected from some neighbouring volcano in active eruption. Immediately behind this cliff rises the Puy de Dallet (6 in woodcut), an isolated hill about 900 feet high above the river, composed entirely of repeated strata of the freshwater limestone and marls, with the exception of a heavy capping of basalt. And in the ravines with which it is scored, sections are afforded sufficient to make it abundantly plain that the beds already described in the cliff alongside the Allier pass under the entire hill.

Some of the strata composing the Puy de Dallet are very siliceous, some oolitic, and the upper beds are of the concretionary indusial variety. The basaltic platform rests immediately on a thick bed which contains much volcanic matter, and is in fact a basaltic breccia, mixed with calcareous particles. It is compact, and seems at a distance irregularly columnar, as is the superimposed basalt.

Here we have unquestionable proof that volcanic eruptions of basaltic lava and scoriæ occurred within or on the banks of the. freshwater lake of the Limagne long before it had ceased to deposit sediment; since a thickness of several hundred feet of its sedimentary beds are found overlying some which contain numerous fragments of volcanic character. In the mountain of Gergovia a similar alternation is to be seen of beds of limestone and marls with others containing numerous fragmentary volcanic matters, often in such abundance as to compose far the greater part of the rock and give it the character of a peperino. This hill also is capped by an enormous platform of basalt and another thick bed of the same rock crops out from the side of

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the hill about a hundred feet lower, the interval being almost wholly composed of horizontal strata of calcareous peperino. It has been questioned whether this latter bed of basalt is a true lava-current like the sheet which caps the hill above it, or is not rather an intruded dyke that has forced itself between the strata ; a distinction of no great importance. It probably partakes of both characters; certainly it is associated with several true dykes which penetrate the calcareous strata beneath it. There can be no doubt, however, of its having been formed before many of the calcareo-volcanic beds which cover it, and which exhibit all the marks of sedimentary deposits accumulated under circumstances of great disturbance from neighbouring and contemporary eruptions.

On other spots of the lake-basin masses of calcareous peperino occur in which stratification entirely disappears. All is confusion, the rock passing by frequent and gradual transitions from a limestone impregnated but slightly with volcanic particles to a calcareous peperino, i. e. conglomerate composed of fragmentary basalt and scoriæ, cemented by calcareous spar, and finally to a compact basalt.

Such examples are found in the Puys de Crouel and de la Poix (remarkable for its abundant bitumen), at Verthaison, Cour-cour, Pont du Château, and the Puy Marmant. In these cases the rock appears to be the result of local volcanic eruptions through the still soft calcareous mud which then formed the bottom of the lake. It is reasonable to suppose that there would have been under these circumstances the most intimate admixture of the calcareous matter with the erupted igneous rock, such as we find here.

At the first of these localities, the hill of Verthaison, a great

* See the description of Gergovia, p. 107 infra.

quantity of fine specimens of radiated arragonite occurs, in veins, some of which are a foot in thickness. They intersect the rock in such numbers as to give it a reticulated appearance. A range of hill consisting solely of the same calcareous peperino is continued for about two miles towards the south.

Above the village of Chauriat it presents a very compact and hard stone, composed of small unequal fragments of augitic basalt firmly united by a fine cement of calc spar. It is difficult, while examining this rock, to believe that the basaltic parts are in reality mere fragments, and the impression is strongly excited that its peculiar structure is owing to a separation of dissimilar substances during the consolidation of a lava which by some mechanical cause had been universally penetrated with calcareous matter.*

La Montagne de Cour-cour, an insulated hill of considerable size rising alone from the plain near Beauregard, is of the same nature. The peperino here is traversed by irregular venous masses of dark-grey basalt. Arragonite is not so abundant as at Verthaison.

The calcareous peperino of the Vicentin (Montecchio Maggiore) exhibits some very similar mixtures of basalt and calcareous spar, which it is difficult to refer decidedly either to the conglomerate or the solid lava-rock.

In giving the name of peperino to a volcanic conglomerate consisting of fragments of basalt and scoria, without pumice or any trachytic matter, united either by simple adhesion or a calcareous or argillaceous cement, I follow the Italian geologists, who have continued this trivial term to a similar rock, which also, like that under consideration, occasionally contains fragments of limestone and primitive rocks, bituminized wood, &c. &c.-Vide Brocchi, Catalogo ragionato di Rocce, pp. 45, 47.

There exists the strongest analogy

between the calcareous peperino of the Limagne and that of the Vicentin, the latter being without doubt the result of volcanic eruptions breaking forth from the bottom of the sea, in which vast masses of calcareous matter (of the Pliocene tertiary formation) lay in a pulpy unconsolidated state; the former of eruptions through a similar mass, the deposit of a freshwater lake. The great variety of rare and beautiful crystallizations to which this violent mixture of calcareous matter with incandescent lava has given rise in both localities, is remarkable. Mesotype, stilbite, arragonite, chalcedony, and numerous forms of calcareous spar, abound in the drusy and vesicular cavities and veins of both these conglomerates.

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The Puys de la Piquette and de Marmont, which rise on the other side of the Allier above Vayre, the first relay on the posting-road from Clermont to Le Puy, are similar examples of amorphous masses of calcareous peperino traversed by vertical dykes of basalt. The latter hill is connected by the base with another of a rather larger size, on which stands the town of Monton, but differs from it in substance. Its principal component rock is like those already described, a peperino of basaltic fragments, small scoriæ, and fine volcanic detritus mingled with fragments of limestone of various sizes, and united by a calcareous cement. On the western side of the hill fronting the Puy de Monton the limestone fragments predominate; the opposite or eastern face consists of an amorphous mass of basalt, hard, solid, and of a dark bluish grey colour, which has here without doubt burst from below through the calcareous sedimentary beds. Parts of this rock are amygdaloidal, being thickly larded with globules of compact radiated mesotype; this mineral having evidently occupied the vesicles formerly existing in the stone. Where the cavity is of a considerable size, it is not filled throughout with the zeolite, but a nest or hollow pouch appears, lined with the most brilliant crystals. These are too well known in all mineralogical collections to require a description here. That variety is most common which consists of radiated groups of large quadrilateral prisms terminated by an obtuse pyramid whose faces correspond with the sides of the prism. Numerous capillary crystals resembling the finest spun glass are sometimes joined with these, but more frequently occupy separate cavities. The same crystallizations are found in cavities of the peperino as well as of the basalt; others present different beautiful varieties of calcareous spar.

The peperino of Pont du Château is equally rich in rare and splendid specimens, which are well known to all collectors of rare minerals.