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I.—On the Volcanic Geology of the Vivarais (Ardêche)
Published online by Cambridge University Press: 17 January 2013
Extract
The limited district of country which I am about to describe, is one of those which may rank amongst the least frequented in the civilized part of Europe, yet which might justly claim for France the character of romantic beauty which travellers on her beaten highways commonly, and not without reason, deny to her.
The modern department of the Ardêche, corresponding in part to the ancient province of the Vivarais, includes country of very dissimilar features, the southern and eastern part, forming the right bank of the Rhone near Viviers, being comparatively flat; whilst the north-western boundary is the irregular chain of the Cevennes, including the localities more immediately to be described. This chain is not so remarkable for its absolute height, although that be considerable, rising at the Mont Mezenc, in the neighbouring department of the Haute Loire, to an elevation of 5750 English feet above the sea, as from forming the separation of a remarkably elevated tract stretching to the north and west, and which suddenly subsides, at the point of which we now speak, into the wide champaign country of the Lower Rhone, possessing a very different aspect, soil, climate, and population.
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- Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 20 , Issue 1 , 1853 , pp. 1 - 38
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- Copyright © Royal Society of Edinburgh 1853
References
page 2 note * Recherches sur les Volcans eteints du Vivarais et du Velay, avec un discours sur les volcans brûlans, &c. Grenoble et Paris, 1778.Google Scholar
page 3 note * These pages were written in 1847.
page 3 note † Bertrand.
page 4 note * See Mr Scrope's Panorama from the Montagne d'Ours.
page 4 note † In clear weather Mont Blanc is visible from hence. Bertrand, Description du Puy, &c., p. 124
page 5 note * Burat Terrains Volcaniques de la France Centrale, p. 230.
page 5 note † Mr Scrope's General Map gives an altogether erroneous idea of the proximity and mutual dependence of the basaltic formations of the Mezenc and those of the Coyrons.
page 6 note * “The uniformly progressive declination of this series of phonolitic summits from the Mezenc to the bed of the river where they terminate, proves them, in my opinion, to be the remains of a single enormous lava current prior in date to the excavation of the actual channel of the Loire, and far the most considerable in bulk and extent of any which I have had occasion to observe in the phlegræan fields of France.”—Scrope's Geology of Central France, p. 129.
page 7 note * Burat, p. 158.
page 7 note † From this point of the description, the map, Plate I., may be consulted.
page 8 note * Burat, p. 4.
page 10 note * That such is the mode of progression of lava streams at a great distance from their origin or after they have been running for a long time, appears from the descriptions of the best writers on volcanoes. Compare Scrope's description of the lava of Etna of 1819, in his work on Volcanoes p. 102; and Auldjo's figure of the descending lava waves of 1831, in his Description of Vesuvius, p. 92.
page 12 note * Measured by the fall of a stone, and confirmed by the authority of a person who told me that he had measured it with a string.
page 13 note * Geologv of Central France, p. 152.
page 14 note * A description of the Western Islands of Scotland, vol. ii.
page 15 note * Examples:—The tributary on the left of Ardêche near Thuez; lava of Burzet at the cascade near the village.
page 15 note † On the authority of Faujas St Fond.
page 19 note * The elevations in this part of the valley were deduced from barometrical observations chiefly made in 1841, and referred to Thuez as a standard height. This latter has been estimated at 1545 feet above the sea at Marseilles from six observations in 1839 and 1841, compared with those of M. Valz at Marseilles, and kindly communicated to me by that excellent observer.
page 21 note * Jameson's Edinburgh Philosophical Journal, 1829.
page 21 note † The specimen illustrating this curious fact, and others referred to in this paper, are now placed in the Museum of the Royal Society of Edinburgh.
page 22 note * About 5 hours' walk across the hills to the south-west of Mayres, or 7 hours' from Thuez (passing le Chambon and Bornes), are the remote mineral-springs of St Laurent les Bains, having a temperature of 125° Fahr. They rise from mica slate, in the neighbourhood of granite, and traversed by granite veins. They contain salts of soda almost exclusively, and particularly the carbonate.
page 23 note * Messrs Lyell & Murchison (Edin. Phil. Journal, 1829, p. 27) speak of angular blocks of unaltered gneiss as occurring near the summit of the Gravenne. These appear to have escaped my notice.
page 25 note * There is also another cottage more to the left, in a place where, on Cassini's Map, is marked “Lac de Ferrand;” that little lake in reality lying higher up in the direction of the volcano of Bauzon.
page 27 note * Bulletin de la Société Géologique de France. Tom. III. and IV.
page 28 note * I am sorry to say, that the view in M. Burat's interesting work on Central France (Plate VII.), is altogether exaggerated and inexact.
page 28 note † 1839, June 3. Spring 42°·0 (Therm. marked A. 1.). 1841, June 25. Spring 42°·2 (Therm. marked A. 3.). Now the correction of A. 3 is +0°·2. That of A. 1 was 0°·0 in 1838. By a singular coincidence the barometer on these two occasions marked the same tenth of a millimetre. The temperature of the air was also within 1° Fahr. of being the same both days.
page 28 note ‡ The mean temperature of Viviers on the Rhone, which is in the same Department, and only 57 mètres above the sea, is 55°·25 according to Cotte, metres as given in Dove's Tables. The crater of Pal is at 1186 mètres above the sea, or 1129 above Viviers. Now, in France generally (according to Martins), the decrease of temperature with height is 1° cent, for 180 metres, or 1° Fahr. for 100 mètres exactly; or 11°·29 for 1129 mètres, whence the mean temperature of Pal should be 55°·25 − ll°·29 = 43°·96. The temperature of the spring was somewhat lower in the month of June, but the approximation is a fair one.
page 30 note * M. de Buch in his early writings (Journal des Mines, XIII., p. 251) notices the olivine of La Barraque, without saying anything as to its origin, except that he considers it an exclusive character of old basalt, as contrasted with lavas, at least in that country.
page 30 note † Scrope, p. 150. Faujas St Fond speaks of the lava at Beaume containing “petits éclats de granit en chrysolite,” which seems to indicate a similar opinion. (Recherches, p. 300.) He also describes masses of olivine existing in the basalt of the valley of Burzet, in the meadows below the village of St Pierre Colombier, weighing as much as 30 pounds. This remarkable statement deserves verification. See Recherches sur les Volcans etcints, pp. 249 and 312.
page 32 note * Barom. 715·6 mm. 26th June 1841.
page 33 note * In the View, fig. 4, the hill behind the cottage of La Fiollonge is of granite, but covered with cinders nearly to its summit. The rocks in front on the left are of granite, but those between the spectator and the cottage in the centre, are of lava, as well as in the lower part of the ravine on the right.
page 33 note † So spelt in the Maps.
page 33 note ‡ Plate XVI. The volume of the River Volane is, however, by mistake, altogether exaggerated.
page 34 note * Recherches, p. 296–298.
page 36 note * The native language of this country, as well as of the Haute Loire, is an almost unintelligible patois. It is more Italian or Latin than French, and is probably the remains of the old language of Provence. The following^Italian phrases struck my ear, “un' ora e mezzo,”—“Aspett' un poc,”—“non ho mai stato,”—“Perchè.”