Ix 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



this disputed question, and to establish as a fact, contrary to the 

 opinion of our late President, that the Jurassic rocks, composed of 

 strata of varied mineral composition, do dip under the crystal- 

 line rocks ; and that little has since been supplied by our fellow- 

 member Mr. Ruskin, who, in a truly practical manner, had a shaft 



Fig. 1. — Relative position of the Limestone in the Valley of Cha- 

 mounix according to M. Favre. 



La Flig^re. Vallee Ue Chamounix. 



N.W 



Aigruillcs 

 Rouares. 



Aiguille Verte de la 

 Chaine du Mont 



Blanc. S.E. 



1. Jurassic rocks. 



2. Anthraxiferous rocks. 



3. Crystalline schists. 



4. Protogene. 



sunk through the intervening detritus and discovered the crystalline 

 schists reposing upon the Jurassic beds ; — a beautiful fact communi- 

 cated to me by letter, and exhibited in the subjoined cuts from Mr, 

 Ruskin's drawing. (See figs. 2 & 3.) We must remember that Dr. 

 Buckland, as well as Saussure and others, came to this conclusion 

 before, and deduced from it the comparatively recent origin of the 

 granite of Mont Blanc ; but, admitting the facts as stated so well by 

 M. Favre, and represented by Mr. Ruskin, we may still hesitate to 

 admit that the crystalline schists ever reposed as non-metamorphic 

 rocks on the Jurassic strata ; indeed, there is no gradual progress of 

 metamorphism to show that such could have been the case. Let us 

 remember that as we pass through the Jura, say, for example, by 

 the Val Travers to Neufchatel, we enter on a disturbed district, many 

 portions of the rocks being evidently in an altered position, — a fact 

 which has been strongly urged by Professor Voigt, in an interesting 

 account of Mont Saleve, as being characteristic of the Jura ; whilst, 

 as Dr. Lombard has pointed out, the occurrence of the same thermal 

 phsenomena at the two extremities of the Jura chain where it ap- 

 proaches the Alpine region marks out the limits of great disturbance, 

 the portions of Jurassic strata which were deposited between the outer 

 belt and the inner focus of disturbance having been thrown necessarily 

 into very abnormal positions. Rejecting then the cleavage-planes in 

 the Jurassic strata, but admitting it in the gneiss, and combining the 

 uplifting of the Aiguilles Rouges on the one hand with that of the 

 Alps on the other, there does not appear any reason why these ap- 

 pearances should be considered anomalous, or the facts disputed. I 

 should, however, add, that Professor Rogers still denies a regular 



