In the Proceedings of the Royal Society, vol. iii., p. 348, an account has been given by Professor Forbes of the discussions which had then taken place as to the geological constitution of the chain of Mont Blanc, and as to the reality of the alleged superposition of the primary rock (gneiss) to the secondary (limestone), near Chamouni, and at Courmayeur.

In order to clear up any remaining doubt, Mr Ruskin caused sections to be made, laying bare the junction at several points of the Valley of Chamouni.