And on the other hand, supposing it probable that all traces of igneous operations had ceased before the earliest period to which history points, there would still be an ample margin left between that and the supposed date of the Flood, to allow of these outbreaks having taken place.

Let us, then, enter upon the inquiry with minds unswayed by any theological bias, and simply consider whether it be probable that, in the passages above alluded to, anything of the nature of a volcanic eruption could have been intended.

And for my own part, as no new arguments have been advanced in support of those alleged by Sir Francis Palgrave, I feel still at liberty to adhere to the opinion which had been taken up long before its possible bearing upon any polemical question was dreamt of, and to maintain, as I did in the year 1819, that the volcanos of Central France have not been shown, by evidence yet adduced, to have been in activity at any period within the range of history or tradition.

And now, having, as I hope, disposed of this previous question, let us proceed to consider whether that class of volcanos which Í denominated post-diluvial, but which I shall now merely designate as, by comparison, modern, presents any characters indicating great antiquity.

În fixing their age, I have derived great assistance from the researches of those eminent geologists who, since the period of my first visit to Auvergne, had explored the district in question, and especially from those of Mr. Scrope, who appears to have spent there the summer of 1821, and of Sir Roderick Murchison and Sir Charles Lyell, who went through the country in 1828.

From the descriptions given by these and other competent authorities, it plainly appears that the valleys in Auvergne were excavated, not at one, but at several successive periods—or, more correctly speaking, that although water was instrumental in their formation, yet that they must have been scooped out, not by any violent movement or sudden passage of a flood over the country, but by the long-continued action of the rivers now in existence.

And if this be the case, it follows, that there can be no abrupt line of demarcation between the older and the more modern volcanic products, and that even those which have been ejected since the formation of the principal valleys, may nevertheless afford evidence of extreme antiquity.

It is but fair to attribute to Mr. Scrope our first correct notions on this subject.

His 'Memoir on the Geology of Central France,' published in 1827, evinces a just idea of the mode in which its valleys were formed, as well as a clear appreciation of the amount of time which must have been occupied in their excavation, and his Work is illustrated by a number of interesting panoramic views, which bring vividly

before us the general Physiognomy of the country, so as better to enable us to realize the force of the evidence he had brought forward.

To this work, and to the memoir of Lyell and Murchison, On the Excavation of Valleys, as illustrated by the Volcanic Rocks of Central France,' I am chiefly indebted for the few facts the space allotted me admits of my bringing forward in proof of the great antiquity even of the more modern class of eruptions.

Let us take the case of the volcano of Chaluzet, near the village of Pont Gibaud.

This is a conical hill, composed of red and black scoria, having on its summit a depression resembling a worn-down crater, from which may be traced a powerful stream of lava descending into the valley below, in which the river Sioule flows. Deflected to the north-west by the lofty and serrated ridge of gneiss which forms the right bank of the stream, the lava-current follows its course as far as "Les Combres," where it terminates.

The upper portion of the mass is scoriaceous, the lower compact and prismatic, and the under-surface of the prisins stands at a height of about 50 feet above the present bed of the Sioule, resting upon a bed of pebbles.

The pebbles have indeed been traced some way into the rock, in consequence of a gallery driven in horizontally through the upper part of the gneiss and the interposed alluvium, so as to render it clear that the lava-stream really rests upon the latter.

The annexed drawing, taken from Sir Roderick Murchison and Sir Charles Lyell's paper On the Excavation of the Valleys in Auvergne,' will illustrate the relative position of the lava-current and gneiss in this locality.

Hence it follows, that since the period at which the lava was ejected, a thickness of 50 feet of solid gneiss must have been excavated.

Now the slowness with which the present river erodes a material of this description may be estimated by a fact pointed out by Sir Charles Lyell in the same province, near St. Nectaire, where an ancient Roman bridge spans the River Couze, over a stream of lava, proceeding from a volcanic hill,-the Puy de Tartaret,showing that a ravine, precisely like that now existing, had already been excavated by the river fourteen centuries ago.

And yet the lava of the Puy de Tartaret presents all the appearance of a modern current, both from its having conformed to the sinuosities of the valley, and also from its covering a bone deposit at its bottom, indicating a mammiferous Fauna, which, although distinct, as a whole, from that now inhabiting Auvergne, presents some features in common with it, as in the existence of the dog, deer, cat, &c., mixed with the remains of the reindeer, which, even so late as the time of Cæsar, appears to have been found in the Great Hercynian Forest, and also with an animal of the horse tribe, differing, however, in some points from the species now living.

But it is in the neighbouring province of the Vivarais that the most remarkable instances of the long-continued action of water slowly eroding to a great depth streams of lava which have flowed at a comparatively recent date, are afforded.

Before describing these, however, I must point out a circumstance which distinguishes a current of lava from one of water, namely, that from its viscid character it has a tendency, near its termination, to accumulate layer upon layer, so that its materials are piled up to a considerable height, instead of spreading onwards, as would happen to a substance of more perfect fluidity.

Hence, when a lava stream reached the bed of a river, it sometimes formed a precipitous bank on one side of it, without appearing to have advanced to the other.

Of this, indeed, several examples are met with in Auvergne, but the most remarkable cases are those to which I have alluded in the Vivarais.

In that province, Mr. Scrope enumerates no less than six perfect volcanic cones, with craters on their summits still preserved in a state of greater or lesser integrity, from which have proceeded streams of lava, each of which may be traced down the sides of the mountain, and are seen to terminate abruptly at its foot.

Now, when the bottom of the valley is occupied by running water, its bank is walled in by a colonnade of basalt, extending for a considerable distance along its margin, derived from the lava stream which had descended from the mountain above.

It is true that when, as sometimes happens, the igneous mass is not perceived on the opposite bank of the river, as is the case at the Coupe de Col. d'Aisac, of which a description and drawing has been given by Faujas St. Fond, we have no right, for the reasons above stated, to ascribe the entire height of the vertical cliff of basalt to the eroding force of water; but, in other cases, as at the spot called the Gravenaire of Montpeset, of which Mr. Scrope has given us a drawing, there can be no mistake about the matter, as a high, precipitous rock, upon which the ruins of a castle stand, is severed from the main body of the lava current, and rises up in the midst of the stream. The upper portion of this rock is composed of basaltic lava, derived from the mountain above and forming the termination of a current which had flowed from it; but the lower consists of gneiss, which, since the lava current had been erupted, is seen to have been excavated by the erosive power of the stream to the depth of 100 feet. The time necessary to bring about this effect I will not pretend to estimate, but may appeal to it as a proof of the great antiquity of a lava current, which must have, at least, been antecedent to its commencement.

One very remarkable peculiarity of the lava streams in the Vivarais currents is their basaltic character and their prismatic structure. We are accustomed to consider trap rocks in general, and more especially that particular description which is denominated basalt, as exclusively the product of submarine volcanos, their compactness being said to arise from the great pressure exercised upon them during their consolidation. But in this part of France we meet with several instances of basaltic colonnades, which have been evidently derived from streams of lava ejected from sub-aerial volcanos.

It is true that, in all those specimens which have come under my notice, minute cells and cavities may be discovered by careful examination, and, moreover, that the upper portions of the bed are more pervaded by them than the lower.

Still the resemblance which they bear to the products of submarine volcanos is very remarkable, and only admits of being explained by the thickness of the bed and the weight of the scoria superimposed, for it evidently matters not in what way the pressure is produced, provided it be sufficient to retain the aqueous and other volatilizable ingredients present within the rock in such a condition as to prevent the production of cells and cavities.

And, accordingly, it is observed, that this compact character and

columnar structure are not met with in those parts of the current which occupy the slope of the mountain, but only at its termination in the valley below, and that even there these characters are confined to the lower portions, where the pressure must have been greatest, the basalt being surmounted by a considerable thickness of cellular lava of the usual kind. Moreover, a difference can be traced in the degree of its compactness according to the relative position which the specimen holds in the basaltic bed, the upper layers being the most cellular.

In the Vivarais, then, as well as in Auvergne, we have abundant instances of lava streams, which, although amongst the most recent the district affords, being poured forth at a time when the general configuration of the country had become nearly what it is at present, exhibit, nevertheless, traces of their high antiquity, from having been subjected to the long-continued operation of denuding agents.

Where these agents have been at work their relative date may be fixed, but we do not appear to possess the same means of referring to a particular epoch the five isolated domes of trachyte which occur on the tableland to the west of the city of Clermont, although the occurrence of free muriatic acid in one of them would imply that they were modern.

These conical hills, of which the loftiest, called the Puy de Dôme, rises to the height of 4,842 feet, or 3,554 feet above the level of Clermont, seem each to have proceeded out of the midst of a kind of crater formed by volcanic rocks of the usual character and appearance, and therefore bearing no analogy to the material of which they are themselves principally constituted. Their general appearance is represented in the annexed woodcut, from a drawing of Scrope's.

FIG. 3.

They seem to bear some resemblance, although on a much larger scale, to the Bosses or Mamelons, to use a French phrase, protruding from the midst of the craters of Rocca Monfina, near Terracina, and of Astroni, near Naples, which may perhaps be paralleled by those dark spots observed by astronomers in the midst of the circular hollows existing on the surface of the moon,