sTATliMKNT BY MR MAK.SH. 



229 



derived have formed shoals in the sea which once beat against the 

 cliffs ; then, by successive deposits, gradually raised them above the 

 surface, and finally expanded them into broad plains traversed by 

 gently flowing streams. If we could go back to earlier geologitial 

 periods, we should find this theory often verified ; and we cannot fail 

 to see that the torrents go on, at the present hour, depressing still 

 lower the ridges of the Alps and the Apennines, raising still higher 

 the plains of Lombai-dy and Provence, extending the coast still 

 farther into the Adriatic and the Mediterranean, reducing the 

 inclination of their own beds and the rapidity of their flow, and thus 

 tending to become river-like in character. 



" We cannot measure the share which human action has had in 

 augmenting the intensity of causes of mountain degradation, and of 

 the formation of plains and marshes below, and we know that the 

 clearing of the woods has, in some cases, produced, within two or 

 three generations, effects as blasting as those generally ascribed to 

 geological convulsions, and has laid waste the face of the earth more 

 hopelessly than if it had been buried by a current of lava or 

 a shower of volcanic sand. New torrents are forming every year 

 in the Alps. Tradition, written records, and analogy concur to 

 establish the belief that the ruin of most of the now desolate valleys 

 in those mountains is to be ascribed to the same cause, and 

 authentic descriptions of the irresistible force of the torrent show 

 that, aided by frost and heat, it is adequate to level Mont Blanc 

 and Monte Rosa themselves, unless new upheavals shall maintain 

 their elevation, 



" There are cases where torrents cease their ravages of themselves 

 in consequence of some change in the condition of the basin where 

 they originate, or of the face of the mountain at a higher level, while 

 the plain of the sea below remains in substantially the same state as 

 before. If a torrent rises in a small valley containing no great 

 amount of earth and of a disintegrated or loose rock, it may, in the 

 course of a certain period, wash out all the transportable material, 

 and if the valley is then left with solid walls, it will cease to furnish 

 debris to be carried down by floods. If, in this state of things, a new 

 channel be formed at an elevation above the head of the valley, it 

 may divert a part or even the whole of the rain-water and melted 

 snow which would otherwise have flowed into it, and the once furious 

 torrent now sinks to the rank of a humble and harmless brooklet. 

 * In traversing this department,' says Surell, ' one often sees, at the 

 outlet of a gorge, a flattened hillock, with a fan-shaped outline and 



