in the Neighbourhood of Cliamounix, in Savoy. 85 



vation, of which the Buet and the Fiz form the northern lip. 

 Lastly, the nearly horizontal beds of the Buet, as stated by 

 M. Saussure (§ 581), and the perfectly horizontal ones of 

 the Aiguille Rouge, are the prolongation of the formations 

 of the two declivities, and leave no doubt as to the ancient 

 formation of this great vault which, from Sixt (about 750 

 metres) rises first to the Buet (3100 metres), then to the 

 Aiguilles Rouges, of which the Jurassic formation alone 

 reached, before the falling down of this great mass, the 

 height of 3750 metres, and descended to Chamounix (1050 

 metres), to be continued perhaps beneath the ground. 



The sedimentary formations, therefore, in this part of the 

 Alps, seem to be arranged not by relation to the central chain 

 of Mont Blanc, but by relation to the chain of the Aiguilles 

 Rouges and the Br event ; and, what is very extraordinary, 

 we cannot discover what has been the influence of the chain 

 of Mont Blanc, in this part of the Alps, on the upraising of 

 the beds. It seems to have had no effect. 



Figure 1 (Plate I.), represents, nearly on a scale of 

 iso^oooj the section taken from Sixt to the Aiguille Verte ; 

 it passes, as will be seen, by the summit of Buet, the Col 

 de Salenton, the Col de Berard, the most elevated of the 

 Aiguilles Rouges, and the valley of Chamounix. This is the 

 only point where the secondary chain of the Buet is not se- 

 parated from the chain of the Aiguilles Rouges by a deep 

 valley. The dotted line indicates the form of the gi*eat vault 

 of Jurassic limestone, and the height to which this formation 

 must have been raised at the time of its elevation. Fig. 2 

 represents the summit of the Aiguille Rouge on a larger 

 scale. The first of these two sketches represents the same 

 chain, and the same assemblage of formations as that figured 

 PI. III., fig. 1, of M. Necker's Memoir on the Valley of Valor- 

 sine.* This section is taken a little more to the north tban 

 that which I give here. The only changes to be made would 

 be to add to my section the granite figured in M. Necker's, 

 and to add to the summit of Mont Loguia, figured by the lat- 

 ter, the horizontal beds of limestone on the summit of the 

 Aiguille Rouge. 



* Memoires Soc. de Physique et d'llist. Naturclle do Geneve, t. iv., ^j. DOD. 



