The landscape now changes altogether, and we are reminded that we have quitted the Lozère for the Aveyron. The air has lost the matchless purity and exhilarating briskness of Sauveterre and Montpellier-le-Vieux. Alike sky, atmosphere, and vegetation recall the south. Pink and white oleanders bloom before every door; the quince, the mulberry, the peach, ripen in every garden. We long to get at our boxes and exchange woollen travelling-dresses for cottons and muslins. Pleasant and welcome as is this soft air, this warm heaven, this bright, rich-coloured, flowery land, we strain our eyes to get a last glimpse of the Causse Noir. To betake ourselves to cosmopolitan hotels, cities and railways, after this sojourn in elfdom, was like closing the pages of 'Don Quixote' or Lucian to read a debate in the House or listen to a sermon. And now that I am no longer held spellbound by wizardry and genii, good or evil, and the first glow of enthusiasm is over, let me jot down a few hard facts for the reader's edification--give in a few words the geological and general history of the Causses, if nothing more--a bare outline to serve the tourist on his way. The origin of the phenomenon is thus explained by the great French geographer, Elisée Réclus, in his chapter on 'Le Plateau Central de la France.' [Footnote: See his 'Géographie Universelle,' vol. ii.: 'La France,' 1885.] 'There is no doubt,' he writes, 'that at a remote period all these plateaux of jurassic rock formed a single Causse, deposed by the sea in the southern strait of the granitic group of France. Although the Causse Méjean, placed almost in the centre of the series of plateaux, is a hundred mètres loftier than the rest, its formation accords with theirs. All show the same features. From the banks of the Hérault to those of the Lot and the Aveyron, all show the same development of continuous strata. The ancient glaciers spread on the highest summits of the Cévennes as they melted, gradually cut into the rock, channelled openings--finally, forcing their way through the layers, have formed these gigantic defiles, now the marvel of geologists. If the rivers flow in an unbroken stream in these deep gorges, on the contrary, water is altogether absent from the plateaux above. The ground, riddled everywhere into holes and fissures, is hardly moistened by a shower. The rain, as if falling through a sieve, immediately disappears. In some places the chasms of rock have widened, the intermediate projections given way, and huge cavities of rightful depth--avens or tindouls, as they are locally called--are formed in the limestone. But the surface of the Causse is almost universally uniform, and these subterranean wells are only indicated by slight openings. Nowhere a foundation springs forth. Alike as to formation, aspect, and climate, the Causses are unique in France.'