72 Professor Favre's Geological Besearches 



the observations which MM. Escher and Studer* have made 

 on the pebbles of Nagelflue, that is, I have seen some of the 

 rolled pebbles forming part of it, which had made an impres- 

 sion on each other ; or, in other words, the convex part of one 

 pebble was embedded in the concave part of another pebble. 

 This fact, however extraordinary it may seem, is less sur- 

 prising in the pudding-stones of Valorsine than in the Nagel- 

 flue, for this pudding-stone appears to have been partly re- 

 melted since its formation. As a proof of this, we may I'efer 

 to the pebbles which are closely soldered, at a part of their 

 circumference, to the cement which encases them, and the in- 

 sensible way in which they and this cement run into one 

 another. If we admit this kind of semifusion, we can readily 

 explain this singular phenomenon of impressed pebbles, for 

 we can understand how rolled pebbles formed of fusible mat- 

 ters could receive the impression of substances less fusible. 



Near Ceblancs we find the rocks of St Jean, in which there 

 is a fissure where ice is formed, even in summer, by the efl"ect 

 of a very rapid current of air. But I could not examine this 

 natural glacier in a somewhat warm temperature, cold and 

 bad weather having followed me during my excursions. 



After traversing for some days the valley of Chamounix, I 

 was very much struck, as MM. De Saussure, Foi'bes, and 

 Necker had been, with the singular position of the masses of 

 limestone observed here and there on the sides and in the 

 bottom of the valley. We perceive that the chain of the 

 Brevent and the Aiguilles Rouges is nearly parallel to that 

 of Mont Blanc. These two great masses of crystalline rocks 

 are separated by the valley of Chamounix, in which stratified 

 limestones occur. It is a very remarkable position for lime- 

 stones to be thus enclosed between two masses of crystalline 

 rocks so extensive and so near each other, the more so as 

 the beds of limestone are very neai'ly vertical at the base of 

 the Aiguilles Rouges, and dip under the chain of Mont Blanc 

 with a great inclination. They thus constitute the structure 



* Actes de la 8oc. Helvetiquc des Sci. Nat. 1837, p. 28 ; 1839, p. 47 ; Annul, 

 des Soc. Geologiques, tome i., p. 228 ; Oouiptes Kendus dc TAcad. des Sc. de 

 Paris, 21 Fcvricr 1818, p. 251. 



