346 OONOLCSION. 



leave all conjectures whatever, take up the facts of the case and look at 

 these in the light of what is known. 



The accounts given of inundations in South Africa may enable sufferers 

 from inundations elsewhere to identify the form of the evil with which they 

 are familiar, with the form of the evil seen in the late inundations in France, 

 these presenting them with an intermediate form having much in common 

 with both J and the identification of this with the torrents of the Alps and 

 other mountain regions of France is not more difficult. Surell spoke from 

 the first of torrents and torrential rivers as essentially identical ; and the 

 evils calling for remedial measures, though varying in the degree of impor- 

 tance attached to them, have been the destruction of the mountains, the 

 covering up of fertile lands in the valleys with sterile detritus, and the 

 inundation of the plains beyond by the superabundant waters. In these 

 inundations we have one of the correlated effedts. And it is in view of this 

 that I have proposed to look at the phenomena of this inundation in the 

 light of what has been ascertained in France in regard to torrential floods 

 and the means of extinguishing them. 



The Alpine torrents are traced by Surell to two sources — the melting of 

 snow about the beginning of June, and storms of rain occurring about the 

 end of summer. The inundations in question have been occasioned by 

 similar causes, but by these operating simultaneously, and this in the 

 Cevennes and in the Pyrenees at the same time. In accordance with what 

 has been stated, when a basin drained by a river is covered with vegetation 

 the flow of the water is retarded, diffused, and protracted ; but when 

 mountains upon which the rain falls are devoid of vegetation, the rain 

 rushes off as does water on the roof of a house, — and thus was it here. 



The Journal des Dehats thus explains the phenomena of these inunda- 

 tions : — 



" It is the chain of the Cevennes which causes these immense disorders. 

 Between the sources of the Loire and the H6rault the Cevennes are 3,700 

 feet high. All this surface is composed of granite impermeable to the 

 rains. The river waters rush over this ground with immense rapidity, but 

 do not enter it. The chief streams rising there are the Dour, the Ervieux, 

 the Ard^che, and the Garden, afluents of the Rh6ne ; on the west, the Lot 

 and the Tarn, affluents of the Garonne ; on the north, the Loire and its 

 tributary the Allier; on the south, the H6rault. The Ard6ohe, whose 

 basin is only 2429 kilometres, has enormous rises. At the bridge d'Arc the 

 stream rises to nineteen metres above the lowest level, and pours down at 

 a rate af 7000 cubic mbtres per second, almost as much as the Loire at 

 Tours. An equal violence is registered in the Dour, the Ervieux, the 

 Gardon, the Is^re, the Drdme, and the Durance. Since everything depends 

 on the rainfall, it is obviously impossible to calculate with certainty before- 

 hand. Every year the Cevennes cause vast ' spates ' in the largest rivers 

 in France — the Ehdne, the Loire, and the Garonne. All the streams of the 

 region are torrents. The southern part of the Cevennes, the Black Moun- 

 tain, and the Corbiferes exercise a great influence on the small Mediter- 

 ranean streams between the Ehdne and the Pyrenees. A rain of 200 

 millimetres, which has no perceptible effect elsewhere, causes in these parts 

 a sudden flood." 



Tn general the rains fall there in May, and being then comparatively cool, 

 they melt but little of the snow, and flow away as they fall. But when they 



