V 

 Notices of Me moin — Prof. Bertrand — Structure of Alps. 227 



the example of Mont Blanc, a great kernel rising in the middle of a 

 Liassic sjncline, which shuts in round it. In the region to which I 

 have devoted special attention, the Vanoise, Mont Pourri, with the 

 Aiguille du Midi, the massif of the little Mont Cenis, and probably 

 that of the Grand Paradis, all owe their existence to a like 

 phenomenon ; on the other hand, the massif of the great Sassiere, 

 and that of the Sana, are due to the sudden broadening of synclinals ; 

 in place of the ancient rocks it is the most recent ones which 

 are here developed, but the system of folds sweeps round these 

 widenings in just the same fashion and opens out and shuts in 

 round them. 



I do not think that we have, at least on a large scale, anything 

 strictly comparable to this amygdaloidal structure, unless it be the 

 crystalline region of the Lake of the Woods in America. Mr. 

 Lawson derives one of his arguments from this structure to prove 

 that the kernels formed of granitoid gneiss are eruptive in origin. 

 Without contesting Mr. Lawson's conclusions on this ground we 

 may point out from the structure of our Alps that this argument, if 

 it stood alone, would be valueless. 



(3) A third conclusion is the generalization of that which M. 

 Termier has already drawn from the study of Vanoise. On the east 

 of the Carboniferous hand metamorphism increases from ivest to east. 

 I am driven, as was M. Termier in the Vanoise, to place confidently 

 in the Permo-Triassic the ancient chloritic gneisses and mica 

 schists of Mont Pourri, little Mont Cenis, and of the Val Grisanche, 

 a continuation of the " Casanna schists " of Gerlach. Most of these 

 arguments apply to the augen gneisses of the Grand Paradis, that is 

 those which have been designated central gneiss ; this would be a 

 last term of the same metamorphism. It is to be noticed that in 

 certain masses like the Dent Blanche and Monte Eosa we see, 

 according to Gerlach, rising like an anticlinal from under this gneiss 

 (or Casanna schist) still more ancient gneiss pierced by numerous 

 granite veins, whilst such veins are absolutely wanting in the 

 massifs previously cited ; this is certainly a new ai'gument. No 

 region offers a more favourable field for continuing those micro- 

 graphic studies so brilliantly inaugurated by M. Termier in the 

 Vanoise, and it is to be hoped that we may be able to follow up 

 in the formation and arrangement of the minerals all the stages 

 to what it is at present convenient to term true gneiss. 



This conclusion is analogous to that which M. Lessen has 

 established for the ancient Hercynian Chain, where the Devonian 

 in a similar central zone, situated, however, rather south of the 

 centre, takes the form of mica schists and gneiss. It is right also 

 to recall that M. Suess in 1869 made out a link between certain 

 gneisses of the Carnic Alps and the Casanna schists in attributing a 

 Permian age to them both. 



I think it right to add that in favour of this last conclusion, at 

 least in its general form, one can at present only give arguments, 

 and not proofs, so that it is as well to separate it from the first 

 twopropositi ons, which appear to me to be definitely established. 



