Page:A book of the Cevennes (-1907-).djvu/43

Rh the limestone area, and cut right through it, separating one Causse from another.

A second feature in the river system of Haute Loire is that a certain number of the affluents of the Loire run into it from the direction in which it is flowing, and their mouths are more or less against the stream they are about to feed. A river usually affects the form of a deciduous tree, of which the branches represent the tributaries. The branches are attached to the trunk at an obtuse angle, as seen from below. With pines it is different; with them the limbs are attached in the reverse fashion, at an acute angle as seen from below. Some of the affluents of the Loire come into it in the way in which a fir branch grows out of the main trunk. This is notably the case with the Arzon and the Borne. The reason for this is that the basin of Le Velay has a rim to the north, and the drainage from the north naturally runs down to the lowest point in the basin. But on reaching this spot the streams come on the Loire, which has cut for itself a huge gap through the northern lip of the bowl, and is able to discharge its waters through that.

How this was done demands some explanation. The Rhone is the mightiest of the rivers of France, but its sources are in the Swiss Alps, and it does not enter France till after it has passed through the Lake of Geneva. But the Loire is next in size and importance, and it flows through French soil only. The source is under the Gerbier de Jonc, in the department of Ardèche, but flows in it for a short course only. It is still a feeble stream when it enters the department of