316 



FALL OF MONT GRENIER. 



if this process take place on both sides of the mountain, the whole 

 of the bed of limestone will fall, except the part which rests flat up- 

 on the summit : in this manner have been left the enormous caps of 

 limestone, like immense castles, that compose the summits of the 

 calcareous mountains, near the lake of Annecy, and in the Bau- 

 ges. — Sometimes the mountain caps, which form an extended range 

 in front, present the appearance of a narrow ridge, when seen in 

 profile. 



The mountain called the Dent d'Alen^on, near the Lake of An- 

 necyj offers a remarkable instance of this. See Plate II. fig. 6. 

 The mass of limestone on its summit, — which I found by trigono- 

 metrical measurement to rise 3840 feet above the lake, and to be 

 nearly five hundred feet in thickness, — was, undoubtedly, once a 

 continuous bed, covering the mountain like a mantle, as represented 

 by the dotted lines : in the course of ages, the side a a has fallen 

 down, and the action of rain on the soft bed, c, on the other side, is 

 undermining the steep escarpment and preparing for its further 

 destruction. The soft bed c c, which forms the talus or slope, be- 

 ing covered with vegetation on the side h c, is in some parts protect- 

 ed from rapid disintegration. On the opposite side of the valley, I 

 found that the thick bed which formed the talus or slope under the 

 limestone, was lias clay. I was not able to ascend the Dent d'Alen- 

 ^on, and therefore did not ascertain whether the bed c was soft sand- 

 stone or lias. In numerous instances, the upper beds of limestone 

 in the mountains of Savoy, may be observed overlapping and over- 

 hanging, as at a a, Plate II. fig. 1., and are thus prepared to fall, 

 whenever the rain and frost has widened the longitudinal natural fis- 

 sures in the limestone. In Plate II. fig. 2., the mountain at y, which 

 had the arched stratification, has been so broken as to present a steep 

 escarpment : such instances are very common in Savoy. The pres- 

 ent state of Mont Grenier, south of Chamberry, and the vast ruins 

 in the plain below, offer a striking illustration of the causes which are 

 in operation, to disintegrate the vast calcareous mountains of Savoy. 

 The following; description, with the cut, is taken from the first vol- 

 ume of my Travels: — " A part of Mont Grenier fell down in the 

 year 1248, and entirely buried five parishes, and the town and 

 church of St. Andre. The ruins spread over an extent of about 

 nine square miles, and are called les Abymes de Myans. After a 

 lapse of so many centuries, they still present a singular scene of des- 

 olation. The catastrophe must have been most awful when seen 

 frofci the vicinity ; for Mont Grenier is almost isolated, advancing 

 into a broad plain, which extends to the valley of the Isere. It is 

 several ^niles in length, and is connected with the mountains of the 

 Grand Ci^artreux, but it is very narrow. Its longitudinal direction 

 is from easito west: near the middle it makes a bend towards the 

 aortb, forming a kind of bay or concavity on the southern side. 



