is soon reduced to pebbles and hurried off. In the Vivarais we shall have occasion to observe this process going on very obviously, and in a manner strikingly suggestive of the prodigious results it is calculated to effect within no very great lapse of time. In the majority of instances, as near Chaspinhac, St. Geneys, Couron, Alègre, &c., the cones rise immediately from granite. That in the neighbourhood of the last town, called La Montagne de Bar, has a large and regular crater at its summit,, about a mile in circumference and 150 feet in depth. A flat area 700 feet in diameter occurs at the bottom, which once contained a small lake or pool of water, but has been artificially drained by a channel cut through the lowest part of the encircling ridge. The lava-streams which descended from the principal range of cones towards the Allier have in a similar manner encrusted the western slope with a thick coating of basalt, and appear to have occupied the former bed of the river nearly in its whole extent from Langogne to Vieille Brioude. The primitive chain of La Margéride, however, rising immediately from the western banks of the Allier, drove the river back upon the basalt that had usurped its channel, and through this, as well as the granite beneath, it has excavated a fresh one. By this process have been disclosed many most magnificent mural ranges of columnar basalt which at St. Ilpize, Chiliac, St. Arçon, Monistrol, &c., encase and frown over the river. They are generally seen to rest upon a bed of water-worn pebbles, from 100 to 150 feet above the present stream, and may be traced eastwards uninterruptedly to the volcanic cones on the slope or summit of the range above. The basalt originating in this linear group of volcanic mouths assumes on different points a very regularly columnar, a tabular, and a spheroidal concretionary structure. It sometimes also separates so readily and to such a degree into small angular globules from the size of a nut to that of a millet-seed, that the roads are strewed with them to the depth of some inches, and the foot often sinks into rocks of this nature as into a heap of gravel. In mineralogical characters the rock varies from distance to distance. Among the remarkable kinds I noticed one with very large spherical cells and an exceedingly crystalline texture; the interlaced grains being felspar, augite, and a bright yellow transparent olivine. It occurs round La Roche on the road from Le Puy to St. Privat; another, near St. George d'Aurat, dense, heavy, and iron-shot, contains still larger oblong cavities frequently coated internally with fiorite. In this range also, as in the Monts Dôme and Mont Dore, we meet with a few lakes occupying wide, deep, and nearly circular basins, which bear every appearance of having resulted from some violent volcanic explosions, but differ from ordinary craters, not only in their greater dimensions, but in the nature also and disposition of their enclosure, which is usually of primary, or, at all events, pre-existing rocks, merely sprinkled more or less copiously with scoria and puzzolana, little if at all elevated above the surface of the environing country. Such are the lakes du Bouchet, de Limandre, d'Issarles, de St. Front, as well as a large and remarkable hollow, now drained, in which the river Fontaulier takes its rise, and which is traversed by the road from Usclades to Montpézat. The latter crater contains a small parasitic cone rising from its bottom. I need not repeat here the remarks upon the peculiar modification of the volcanic phenomena to which this variety of crater apparently owes its formation, which were sufficiently dwelt on in the description of the Gour de Tazana.* Between Pradelle and Aubenas the cones diminish in number, rising here and there through the great forest of Bauzon, and showing themselves up to the escarpment of the elevated platform of the Haut Vivarais. * P. 81. But the most remarkable and interesting by far of the recent volcanic remains of the zone we are now considering, and perhaps of all France, are those that occur on the steep declivity by which this escarpment is connected with the great southern valley or low-lands of the Bas Vivarais and Languedoc. I have already described the primary table-land as abruptly cut down on this side. Its rapid slope is intersected by deep mountain gorges, into which frequently open the transverse trough-shaped valleys of the coal formation. Viewed from below, this front of the great platform appears as a precipitous curtainlike range, broken by recesses into short, steep, and massive promontories, in which all the rude and stupendous scenery of a granitic mountain district is displayed in its full magnificence.* It is therefore an unexpected and striking contrast that is presented by a few single and regular volcanic cones perched at distant intervals upon the rocky ridges of these granitic embranchments; nor is it less surprising to find the gorges that sever them almost choked up to some distance by enormous flat-topped beds of columnar basalt, such as we have been accustomed only to observe as the cappings of elevated hills. These remarkable characters belong to six different points of eruption, designated by the six very perfect volcanic cones of Montpézat, Burzet, Thueyts, Jaujac, Souillols, and Ayzac. 1. The first, called by the peasants La Gravenne de Montpézat, from the puzzolana or "gravier" of which it chiefly consists, is a It would be perhaps difficult to find, in any range of mountains, scenes which present a more exquisite combination of beauty and magnificence than some of the valleys of the Bas Vivarais, so little visited by hunters of the picturesque. The rich glow of their chesnut forests, tinted by a soft and brilliant atmosphere, is far more adapted to painting than the cold transparent colouring of the Alps and Pyrenees, their pine-forests and waterfalls; nor can the outline of their masses be considered as much inferior in grandeur. The scenery is in fact that of the Apennines, but with a more luxuriant vegetation than that great limestone range can support. |