XIV.] THE GEOLOGY OF THE ALPS. 347 



APPENDIX. 



[THE crystalline rocks in the line of the Mont Cenis Tunnel, con- 

 sisting of micaceous limestones, dolomites, gypsums, and anhydrites, 

 with talcose schists, serpentines, and quartzite, have been, as we 

 have seen, regarded by all observers as altered mesozoic strata. 

 According to Elie de Beaumont and Sismonda, they are metamor- 

 phosed Jurassic, and the uncrystalline anthraciferous strata in con- 

 tact with them near Modane are unaltered rocks belonging to the 

 same period. Favre, on the other hand, while maintaining the car- 

 boniferous age of the latter, followed Lory in regarding the crystal- 

 line strata as more recent than these, and, in fact, as metamorphosed 

 triassic. These conclusions as to the age of the crystalline rocks I 

 have ventured in the preceding pages to call in question, and have 

 compared them with certain ancient crystalline schists of Scandi- 

 navia. A letter from Professor Favre, dated February, 1872, admits 

 the justice of my strictures ; he now rejects the notion that they 

 are altered fossiliferous strata, and regards them as of unknown age, 

 citing the recently expressed opinion of Gastaldi that they are older 

 than the carboniferous and are altered paleozoic. The existence 

 of such rocks of paleozoic age is, however, improbable, and those 

 to which I have compared them are eozoic. 



Professor Favre writes, with reference to my ideas as expressed in 

 the above review and also in my address at Indianapolis (ante, pages 

 286-312), as to the possible alteration of palaeozoic and more re- 

 cent strata to crystalline schists : " Je vois avec grand plaisir que 

 vous n'y croyez guere, puisque vous ne voyez nulle part des schistes 

 cristallins dont on puisse dire que ce sont des schistes paleozoiques 

 alteres. Je suis arrive a croire qu'il n'y a pas de metamorphisme 

 pour les terrains en grand, au moins bien peu, et que tous les ter- 

 rains se sont deposes a peu pres dans 1'etat oil nous les voyons."* 



* " I see with great pleasure that you have little belief in it " (the alteration 

 of palaeozoic and more recent strata to crystalline schists), "since you nowhere 

 recognize crystalline schists of which it can be said that they are altered 

 palaeozoic schists. I have come to believe that there is little or no metamor- 

 phism for the great formations, and that all these formations were deposited 

 very nearly in the state in which we see them." With the above extract from 



