18 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 15, 



peculiarities of interest ; it exhibits the junction of two beds of gypsum 

 of very different characters, separated by an irregular waving line, 

 which is on the whole vertical, striking E. The southern portion is 

 traversed by well-marked planes of cleavage, dipping S. 70°, along 

 which are small folia of talc, giving the mass a grey colour. The 

 northera bed is a pure white gypsum, quite free from cleavage ; the 

 annexed woodcut, fig. 1, will give a rough idea of this arrangement. 



Fig. 1. 



S 1/ 



A / 

 / Y / \ 



/ -'1 / / 



1 1 > I 





Talcose Gypsum. Pure white Gypsum. 



It appears from these sections that there are two deposits of gypsum 

 of very different ages in the valley of Chamoanix ; the earlier one 

 laminated, the later deposited after the lamination of the rocks was 

 completed. In both these cases the detritus concealed the base of 

 the gypsum. 



The lower part of the valley of Chamounix is so much filled up 

 by detritus that I despaired of finding anywhere the central axis of 

 the valley exposed ; but since my return I observe that Saussure 

 mentions at § 656, that at Blaitiere, to the east of the village of 

 Chamounix, the foliation of the crystalline schists is nearly hori- 

 zontal, striking N.E., from which spot the inclination gradually in- 

 creased as he ascended towards Mont Blanc. This observation bears 

 out what I had inferred, that the foliation of Mont Blanc and the 

 Aiguilles Rouges forms together a complete arch, the crown of which 

 runs down the valley of Chamounix. 



In Section No. 5, PI. I., I have given a rough sketch of the posi- 

 tion of the bedding and cleavage of the rocks seen in crossing the Col 

 du Bonhomme from Nant Bourant to Chapieux. The Bonhomme is 

 exactly on the southern prolongation of the western line of vertical 

 foliation of Mont Blanc. The section is a most interesting one, and 

 worthy of more time than I devoted to it ; but as M. Favre is engaged 



