348 



2. On the Geological Relations of the Secondary and Pri- 

 mary Rocks of the Chain of Mont Blanc. By Professor 

 Forbes. 



This paper* is intended to meet the objections taken by Mr D. 

 Sharpe, in a paper published in the Quarterly Journal of the Geo- 

 logical Society for February 1855, to the views of the present 

 writer, and those of several eminent geologists, on the structure of 

 the chain of Mont Blanc. 



De Saussure first described the singular superposition of gneiss to 

 limestone which occurs on the south-east side of the valley of Cha- 

 mouni, a testimony the more clear from its obvious opposition to 

 the Wernerian views of the period. 



]Vr. Necker, grandson of De Saussure, in a remarkable paper on 

 the granite of Valorsine, published in 1828, presents a section of 

 the south-east slopes of the valley of Chamouni, which exhibits the 

 limestone dipping under the gneiss, the beds of which gradually be- 

 come steeper as we approach the centre of the chain. The facts 

 were still more emphatically stated by the same author in a work on 

 the Geology of the Alps, published thirteen years later. 



In 1842, Professor Forbes paid particular attention to the struc- 

 ture of both sides of the chain of Mont Blanc ; and pointed out the 

 precise analogy of the superposition of gneiss to limestone on the 

 Italian, to that on the Swiss side of the mountain. He indicated 

 very distinctly two localities, one on each side of the Alps, where 

 the superposition might be distinctly seen and traced for some dis- 

 tance. 



Mr Sharpe, in the paper referred to, having treated the descrip- 

 tions of De Saussure and of M. Necker as vague or contradictory, 

 the present writer defends them. And he repels Mr Sharpe's 

 objection to his own conclusions as not based on sufficiently definite 

 indications of the localities, by citing the passages from his Travels 

 in the Alps, where he has specified them, and by showing that other 

 geologists have satisfactorily verified his observations. 



He next quotes the testimony of M. Favre of Geneva, and of M. 

 Studer of Berne, as having from personal observation of the closest 

 kind, been led to conclusions identical with his own. 



* It will be printed at length in the Edinburgh New Philosophical Journal 

 for April 1856. 



