The masses of limestone are cleft with _clus_, gorges through which the rivers thunder, and _foux_ springs of living water bursting out of the bowels of the mountains.
Consider what the variety of geologic formation implies: an almost infinite variety of plants; moreover, owing to the difference of altitudes, the flora reaches in a chromatic scale from the fringe of the Alpine snows to the burning sands by the seas. In one little commune, it is estimated that there are more varieties to be found than in the whole of Ireland.
But the visitor to the seaboard—the French Côte d’azur and the Italian Riviera—returns home after a winter sojourn there with his mind stored with pictures of palms, lemons, oranges, agaves, aloes, umbrella pines, eucalyptus, mimosa, carob-trees, and olives. This is the vegetation that characterises the Riviera, that distinguishes it from vegetation elsewhere; but, although these trees and shrubs abound, and do form a dominant feature in the scenery, yet every one of them is a foreign importation, and the indigenous plants must be sought in mountain districts, away from towns, and high-roads, and railways.
These strangers from Africa, Asia, Australia and South America have occupied the best land and the warmest corners, just as of old the Greek and Roman colonists shouldered out the native tribes, and forced them to withdraw amidst the mountains.
The traveller approaching the Riviera by the line from Lyons, after passing Valence, enters a valley that narrows, through which rolls the turbid flood of the Rhone. Presently the sides become steeper, higher, more rocky, and draw closer; on the right appears Viviers, dominated by its cathedral and tower, square below, octagonal above, and here the Rhone becomes more rapid as it enters the _Robinet de Donzère_, between calcareous rocks full of caves and rifts. Then, all at once, the line passes out of the rocky portal, and the traveller enters on another scene altogether, the vast triangular plain limited by the Alps on one side and the Cevennes on the other, and has the Mediterranean as its base. To this point at one time extended a mighty gulf, seventy miles from the present coast-line at the mouth of the Rhone. Against the friable limestone cliffs, the waves lapped and leaped. But at some unknown time a cataclysm occurred. The Alps were shaken, as we shake a tree to bring down its fruit, and the Rhone and the Durance, swollen to an enormous volume, rolled down masses of débris into this gulf and choked it. The Durance formed its own little _crau_ along the north of the chain of the Alpines, and the Rhone the far larger _crau_ of Arles, the pebbles of which all come from the Alps, in which the river takes it rise. But, in fact, the present _craus_ represent but a small portion of the vast mass of rubbish brought down. They are just that part which in historic times was not overlaid with soil.