FALL OF MOUNTAINS. 



319 



and night. The mountain did not, like that of Mont Grenier, fall at 

 once, for it is composed of a succession of beds of limestone resting 

 on sandstone, and extremely fragile schist, which are even now yield- 

 ing to the constant action of rain. A deep excavation, which I ob- 

 served under a precipice of limestone, near the summit, appeared in 

 1821 to threaten a renewal of the catastrophe of 1751.^ 



In the Swiss Alps, the great ehoulements\ which have destroyed 

 whole villages, have been caused by the sliding down of highly in- 

 clined beds of loose conglomerates, which have been undermined at 

 their bases. This will be belter understood by a reference to Plate 

 II. fig. 2., representing the section of a mountain on the Alps : the 

 beds a a b a b are highly inclined ; and should the outer bed a be a 

 soft sandstone or conglomerate, the action of w^ater-courses or heavy 

 rains upon its foot or base tends to destroy and undermine it, and the 

 whole bed, perhaps several hundred feet in thickness, is suddenly 

 precipitated into the valley. In 1806, a part of the mountain of 

 Rosberg, between the lakes of Zug and Laworts, fell down from the 

 cause here mentioned, and buried a considerable part of the valley, 

 and several of the inhabitants. 



Where the soil is favorable to vegetation, the debris, or ruins from 

 the fall of mountains, become covered with vineyards and chestnut- 

 trees ; of which we have an example in the soil that covers the 

 former town of Pleurs, near Chavennes, and all its noble palaces, 

 belonging to opulent citizens of Milan. On the 26th of August^ 

 1618, " an inhabitant entered the town, and said that he saw the 

 mountains cleaving : he was laughed at for bis pains ; but in the 

 evening the mountain fell, and buried the town and all its inhabitants. 

 The number destroyed is stated to be 2430, oi' whom not one es- 

 caped, except the person who warned them of their danger." 



Where the soil is unfavourable to vegetation, the ruins remain ex- 

 posed to the action of rains, and of torrents from the sudden melt- 

 ing of snow, which furrow channels through them, and leave detach- 

 ed monticules, as in the Abymes de Myans ; but it is evident, that by 

 these causes they could not be transported to distant countries, ex- 

 cept in the comminuted form of sand or mud. 



There are, however, other causes in present activity, which tear 

 down large masses of rock, and carry them many miles from their 



* In an Essay sur les Caracttres Zoologiqucs, by M. Brongniart, published in 

 1822, he has given a section of this mountain ; and from the fossils in the upper 

 bed, and the green sand intermixed, he has, with mnch probability, classed it with 

 the chalk formation. The lower beds of the monntain, containing ammonites, he 

 still classes xvith transition rocks; but I am persuaded that these lower beds are 

 not more ancient than the English lias, or the blue beds of the magnesian lime- 

 stone: and in this mountain, (Montague de Fis,) we have all the upper secondary 

 strata of this- part of Savoy in one group. 



t The fall of parts of mountains is so common an occurrence in the Alps, that 

 it is expressively called an 6bouleme7it, from the verb ibouler. In Devonshire and 

 Dorsetshire, the fail of the cliffs is called a rougement. 



