MOUNTALN SLIDES. 281 



the left bank of the Arno at Florence — ^forms a part, was deeply 

 fissured by cracks which seemed to threaten extensive slides; 

 and similar observations were made in other parts of Tuscany. 

 The journals of Savoy announce that the forests of Joigny, at 

 Combe, Mont-Granier, in that province, covering two square 

 kilometres, has shd down the hill of Entremont, in the direction 

 of the village, and its inhabitants have abandoned it. The heavy 

 rains had saturated the ground and then formed torrents which 

 undermined the foot of the hill. 



Such displacements of earth and rocky strata rise to the mag- 

 nitude of geological convulsions, but they are of so rare occur- 

 rence in countries still covered by the primitive forest, so com- 

 mon where the mountains have been stripped of their native 

 covering, and, in many cases, so easily explicable by the drench- 

 ing of incohesive earth from rain, or the free admission of water 

 between the strata of rocks — ^both of which a coating of vegeta- 

 tion would have prevented — that we are justified in ascribing 

 them for the most part to the same cause as that to which the 

 destructive effects of mountain torrents are chiefly due — the fell- 

 ing of the woods. * 



In nearly every case of this sort, the circumstances of which 

 are known — except the rare instances attributable to earthquakes 

 — ^the immediate cause of the slip has been the imbibition of 

 water in large quantities by bare earth, or its introduction be- 

 tween or beneath soHd strata. If water insinuates itseK between 

 the strata, it creates a shding surface, or it may, by its expansion 

 in freezing, separate beds of rock, which had been nearly con- 

 tinuous before, widely enough to allow the gravitation of the 

 superincumbent mass to overcome the resistance afforded by in- 

 equahties of face and by friction ; if it finds its way beneath hard 

 earth or rock reposing on clay, or on other bedding of similar prop- 



* There is good reason for thinking that many of the earth and rock slides 

 in the Alps occurred at an earlier period than the origin of the forest vegeta- 

 tion which, in later ages, covered the flanks of those mountains. — See Bericht 

 iiber die Untersuchung der Schiceizerischen HochgebirgswaMungen, 1862, p. 61. 



Where more recent slides have been again clothed with woods, the trees, 

 shrubs and smaller plants which spontaneously grow upon them are usually of 

 different species from those observed upon soil displaced at remote periods. 

 This difference is so marked that the site of a slide can often be recognized at 

 a great distance by the general color of the foliage of its vegetation. 



