Wavre— Structure of Mont Blanc, IX 



ABSTRACTS OF BRITISH KM FOEEiaN MEMOIRS. 



L — Ots. the Structure of Mont Blanc. 



By Alphonse Favee. 



lA Structure en eventail du Mont-Blanc, par Alphonse Favee. (Tir6 

 de la BibliotMque universelk et Revue Sukse de Novembre 1865.) 



FAVEE here describes a peculiar arrangement of the stratifica- 

 tion, called ihe fan-like (''en eventail") structure, seen in 

 most of the Alpine massives foj-med of Crystalline rocks ; and dis- 

 cusses the aqueous origin of Protogine and Granite. 



The structure, "en eventail," as explained by M. Lory, is "the 

 remains of a large vault formed by Protogine rocks under the 

 influence of lateral pressure," and M. Favre agrees with this view. 

 It, however, requires that the aqueous origin of Protogine be 

 admitted, for if the Protogine had burst forth in a molten state, 

 it would have run out and settled down without forming any 

 considerable elevation. When the rocks took their present position, 

 their hardness must have been nearly complete. M. Favre, there- 

 fore, considers Protogine as having been deposited under water, not 

 as an ordinary sedimentary deposit, afterwards altered by metamor- 

 phism, for then the stratification would have been obliterated, which 

 is not the case ; but in seas whose temperature was very high, and 

 whose conditions and properties were quite different from those of 

 the present time. M. Rose, he observed, had determined that quartz 

 was formed solely by the agency of water ; and it was evident that 

 tiie crystals of felspar, disseminated in great abundance in the 

 Magnesian Limestones of the Alps, must have been similarly 

 deposited. Talcose and micaceous substances must also have owed 

 their origin to reactions in wliich water was the most important 

 agent. iSe stated that impressions of fossil plants from the coal of 

 Petit-Cceur, in Tarentaise, were covered with a fine pellicle of white 

 glittering material, which, on analysis, proved to be mica ; this could 

 not have been deposited otherwise than by water. 



If, therefore, Protogine and all granitic rocks had an aqueous 

 origin, whence were they derived? From a recent observation of 

 Dolomieu, in Auvergne, Lava (taking the word in its broadest sense) 

 •was seen to pierce Granite, which has been supposed to form the 

 basement of all other known rocks ; he concludes that, as Lava is 

 proved to be older than Granite, the latter, as well as other rocks, 

 may have been derived from it, and that, consequently there is but 

 one true igneous rock, namely, Lava. 



H. B. W. 



