still to appear cascading over the lips of craters of scoriæ, did assist in no small degree in putting an extinguisher on the then fading and flickering, but shortly before insolently triumphant, dogma. It had, likewise, I may hope, some share in directing attention to the vast influence exercised on the crust of the earth, not only by volcanic outbursts, but also by the erosive forces of rain and rivers, acting slowly and gradually, but through periods of immeasurable duration, upon the surface of supra-marine land.*

The edition of this Memoir printed in 1826 soon became exhausted. I was, however, unwilling to reprint it without previously revisiting the country of which the volume treats, and convincing myself of the accuracy of its descriptions; but it was only in the course of the past summer that I succeeded in accomplishing this.

Meantime Sir Charles Lyell and Sir Roderick Murchison, and many others, had followed me to Auvergne, and I had reason to believe were satisfied with the fidelity of my views and descriptions. The French geologists have also since that time paid more attention to this most interesting portion of their country than they had previously given to it. And I have been gratified to find many of the most trustworthy among them put forward views coinciding with

* See last note.

my own upon the several problems which there offer themselves for solution. I may instance M. Constant Prevost, whose ideas on the volcanic formations of that country, as expressed in a paper read before the Geological Society of France in 1843,* are identical with those which form the staple of my original volume. So likewise are those of M. Bertrand de

†M. C. Prevost, as well as M. Pissis, and some other practical observers, have, with good reason, from the first, endeavoured to stem the current of opinion, which, among the Parisian geologists for some years so unfortunately set in favour of that most unphilosophical theory of "Elevation Craters," first suggested by M. de Buch, and afterwards warmly espoused by MM. Elie de Beaumont and Dufresnoy. Next to the exploded theory of Werner, I know of no fallacy that has so much impeded the march of true science, or been so obstinately persisted in. Such a notion could only find favour with geologists who had never witnessed the phenomena of volcanic eruptions on a large scale, and consequently had no conception of the normal mode in which their products are disposed. To one who has had that advantage, the theory does not appear to merit serious discussion. Pushed as it has been to extremity by the two last-named authorities, it in fact denies a volcano to be eruptive at all, that is to say, to be productive of any appreciable amount of lava or fragmentary matter; since such products, if they really accompanied in enormous quantities (as observers have been in the habit of believing from the evidence of their senses) the often repeated eruptions of active volcanos, must have accumulated about the orifice in the form of a mountain composed of those same multiplied beds of intermingled lavas and conglomerates, which these geologists persist in asserting not to have produced the mountain or its parasitic cones, which our eyes see them at work upon, but to have filled some supposed pre-existing hollow, afterwards raised by some sudden and anomalous process into the form of a mountain! It has never, of course, been denied by any sound writer on volcanic action, that a certain proportion of the frame of a volcanic mountain may have been partially elevated by those expansive throes or earthquake shocks which usually precede or accompany every eruption, and attest the production of fissures through its solid framework: which fissures being filled by the intumescent lava welling up from below, will no doubt when this is consolidated within them in the form of dykes, permanently raise and add in some degree to the bulk of the mountain, by what Sir C. Lyell

Doue, ably given in his description of the environs of Le Puy. MM. Le Coq and Bouillet have done me the honour to take many of my panoramic and other views as models for the illustrative engravings to their different works on the geology of Auvergne. Messrs. Rozet, Pissis, Ruelle, and others, many of whom were employed on the Government Geological Survey of the country, still in progress under the Ecole des Mines, have also printed or communicated to the Geological Society of France papers of interest on the tertiary and volcanic formations of Central France. Great light has likewise been thrown on the Palæontology of this district by the zealous researches and

aptly calls an "inward growth." Observations on the amount of matter composing the dykes, which are so frequent towards the centre of every volcanic mountain, would indicate perhaps a proportion of one-sixth or less of the substance of the central part of the cone as having been formed in this manner. And in some such proportion, elevation, in the sense implied by the elevation-crater theorists, may be admitted to have assisted in the production of the central summits. But at a distance from these few dykes are found, and there is no reason to doubt that the great bulk of such mountains owes in every case its formation to the heaping up of ejected matters, whether fragmentary or in the form of congealed lava-currents; a process which in fact may be witnessed in active volcanos, as the normal phenomena of every eruption. Any other view seems to me opposed not merely to the rules of philosophical analogy, but even to the evidence of the senses. The weight of authority unfortunately thrown into the scale in favour of this theory by geologists of such repute and influence as MM. de Beaumont and Dufresnoy has been the leading cause of the uncertain views and imperfect knowledge even now existing among French geologists on the great extinct volcanos of their own country. The clue to an understanding of a volcanic district must of course be a sound knowledge of the "modus operandi" of volcanic action; and this has been wanting in the modern school of Parisian geologists, with the exception of some few, who, like MM. Prevost and Pissis, above mentioned, have had the courage to oppose the influence exercised by two or three "great names."

able publications of MM. Croizet, Jobert, Bravard, Aymard, and Pomel.

The publication of the Explication de la Carte Géologique de la France,' by MM. Elie de Beaumont and Dufresnoy, has not yet reached those chapters in which the preface professes an intention to treat of the tertiary and volcanic formations of Central France. M. Le Coq is, I believe, engaged on a general work of this nature on Auvergne, to be illustrated by a geological map. But no portion of this work either has as yet been made public.

Under these circumstances, none of the publications, whether of French or English writers, which have yet appeared can be considered to afford that general view or detailed description of the very remarkable series of geological facts presented by this country which they undoubtedly merit, or which any visitor desirous of examining its phenomena would wish to have in his hand as a guide. I have therefore been led to suppose that a new edition of my Memoir, with such emendations and additions as time and the further observations, whether of myself or others, might suggest, would be acceptable at the present time. It will be seen that though I have found it desirable to recast some of the introductory chapters, the body of the work is still the same as was printed in 1826. Indeed on my late visit, I found no reason to alter the conclusions I had come to in 1821. Not possessing sufficient acquaintance with

Paleontology to venture on determining, of my own authority, the specific characters of the organic remains found in association with the rocks, whether tertiary or post-tertiary, of the district, I have given catalogues of its fauna from the works of MM. Pomel and Aymard in an Appendix, to which the text refers at the proper place. The illustrations have been recast and engraved on wood on a reduced scale, for the advantage of their being folded into the compass of an 8vo. volume, instead of necessitating, as in their original shape, an inconvenient accompanying folio atlas.

Of the maps, that of the Chain of Puys west of Clermont is nearly in the same state in which it appeared in the first edition. And I may add that it was entirely compiled from my own observations on the spot, on the basis of a sheet of Cassini's old Survey, as I had no access at the time to Desmarest's map, from which it has, I believe, been supposed that I took the details.

6

The other general map of Central France is copied from the Carte Géologique de France,' of MM. de Beaumont and Dufresnoy.