3S0 Revieics—M. Michel-Levy— On Mont Blanc. 



its more natural place amongst the LituiticlsB, which has been given 

 to it by Barrande." 



We desire in closing to express our sincere appreciation of the 

 valuable service the author has rendered to palaeontological science 

 in collecting and expounding so many new and interesting facts 

 regarding a hitherto but half-understood genus. We trust he will 

 permit us also to add our congratulations to him upon his admirable 

 handling of our mother-tongue. A. H. F. 



The Geology of Mont Blanc. 



IV. — " Etude sur les Boches cristallins et eruptives des 

 environs du Mont Blanc." By M. Michel-Levy. (Bull, 

 serv. Carte geol. France, No. 9, Paris, 1890.) 



THE old view of the geological structure of Mont Blanc repre- 

 sented the valley of Chamounix as occupied by a synclinal of 

 Jurassic rocks, nipped in between the schists and gneisses of the 

 anticlinals of the Aiguilles Rouges on the west and of Mont Blanc 

 on the east. This view has been widely circulated owing to the 

 frequent quotation of A. Favre's diagram, in which it is so well 

 expressed. It has not however, during the past few years, been 

 allowed to pass unchallenged. Lory regarded the fact of the schists 

 on the west flank of Mont Blanc dipping eastward, and those to the 

 east dipping westward, as due simply to an ordinary synclinal, and 

 not as a case of the "fan structure." According to this theory, the 

 central " protogine gneiss," which ftynns the main mass of the 

 mountain, is newer than the schists upon its lower flanks, while the 

 crystalline rocks are faulted up against the Mesozoic beds of the 

 Chamounix valley. Mazzuoli on the other hand regards Mont Blanc 

 as an anticlinal, and the protogine as part of the old " fundamental 

 gneiss," covered to east and west by newer but yet pre-Pala^ozoic 

 schists. It is clear that in these conflicting hypotheses, the whole 

 question turns upon the nature of the " protogine " and its relations 

 to the surrounding schists. M. Michel-Levy has therefore subjected 

 this rock to a careful examination, and in the above memoir claims 

 the protogine to be a true granite, intrusive into the schists, and 

 subsequently itself foliated by lateral pressure. This view is sup- 

 ported, first, by a microscopic study of the protogine and its 

 principal varieties, such as the amphibolic protogine, an altered 

 specimen of which was recently described by an English author as 

 an epidiorite. Second, by an examination of the relations of the 

 protogine to the schists, into which it is proved to send numerous 

 veins ; the junction of the two rocks is not well shown in the great 

 sections of the valleys of the Glacier d'Argentiere and the Mer de 

 Glace, but clear proof of the intrusive nature of the protogine can 

 be seen above Pierre Pointue and round the Aiguille du Plan. Third, 

 by a microscopic study of the " englobements " so numerous near the 

 junction with the schists. M. Levy rejects Prof. Rosenbusch's view 

 that these are segregations of the first period of consolidation, and 

 argues that they are included fragments of the schists. 



