84 Vro^e^^ovYskVYQ'^ Geological Researches 



rous formation, and particularly those of the sandstone, ai-e 

 slightly undulated and modelled on the asperities of the 

 crystalline ground. They occupy a small part of the northern 

 slope of the aiguille, and are raised against the great Alps. 



I shall not state the other observations I made in this loca- 

 lity. My object is not to enter into minute details in this 

 place, but to throw a glance at the general structure of this 

 part of the Alps. It is evident that the rocks on the sum- 

 mit of this Aiguille Rouge are a prolongation of the lower 

 part of the sedimentary formations of the Buet, and of those 

 which rest upon the base of these aiguilles in the valley of 

 Chamounix. Now, I estimate the thickness of the Jurassic 

 formation, by means of barometrical measurements, at 800 

 metres at least ; consequently, if there were no sinking down 

 immediately after elevation, and no denudation since that 

 time, the Jurassic formation would rise on the Aiguilles 

 Rouges, at least to the height of 3750 metres (a fig. 1), and 

 the Buet, of the height of 3100 metres, would be the north- 

 ern declivity of this great mountain, and not, as it seems 

 now to be, the principal chain. 



We must consider the chain of the Aiguilles Rouges as a 

 great mass of crystalline rocks, extending from Servoz as far 

 as the banks of the Rhone, near St Maurice in the Valais. 

 It is flanked on the north-west side by the great Jurassic 

 chain of Buet, the prolongation of which, to the south-west, 

 is crowned by the cretaceous limestones of Fiz, and which is 

 continued to the north-east as far as the Dent du Midi, above 

 St Maurice. The beds of this great secondary chain are 

 raised up to the south-east against the chain of the Aiguilles 

 Rouges and the Brevent. Passing along the escarpment 

 which it presents on this side, we can examine all the nu- 

 merous and varied formations comprised between the num- 

 niulitic beds and the crystalline slates. All these beds ap- 

 pear, therefore, to form the northern base of a vault or 

 gigantic elevation, the beds of which must have passed below 

 the Aiguilles Rouges. 



On the south-east, this chain is likewise flanked by the 

 formations of the valley of Chamounix and the Col de Balme, 

 which are upraised against the Aiguilles Rouges. They ap- 

 pear to form the southern base of the great vault or ele- 



