Reports and Proceedings — Geological Society of London. 381 



If the valley of Chamounix be a synclinal, then there should be 

 some agreement between the sequence of the schists on both sides of 

 the valley. M. Michel-Levy divides the schists into three zones. 

 The western includes three main types : the granulitic mica-schists 

 (i.e. schists injected by granulite) of the Aiguille de Berard, Aiguille 

 cotee, the amphibolites and eclogites of Lac Cornu, and the coarse 

 mica-schists of the Brevent. The median zone is a series of mica- 

 schists, which extend from the Col du Montet, past the Flegere, 

 and below the Planpraz, along which line they form the slopes at the 

 foot of the crags formed by the coarse schists of the first zone ; very 

 similar rocks to these occur at the end of the Glacier des Boissons. 

 The eastern zone is constituted of mica-schists, associated with some 

 amphibolites, and analogous to the rocks of the western zone : this 

 zone can be well studied in the valley of the Mer de Glace, where 

 the schists alternate with interstratified granulites, while both are 

 cut by veins of aplite. Hence though the evidence is inconclusive, 

 the existence of a synclinal is probable. M. Michel-Levy hopes to 

 obtain more satisfactory proof during the coming season. 



The age of the protogine cannot be exactly determined. It is 

 pre-Carboniferous, as fragments of it occur in the Carboniferous con- 

 glomerate of Ajoux ; it is later than the pre-Cambrian schists (z" and 

 probably also x of the French Survey), and so is much younger than 

 the Italian geologists admit. 



In addition to the main question discussed in the memoir, valuable 

 contributions are made to the discussion of collateral subjects. 

 Thus the author claims that the microgranulite of La Poya supplies 

 conclusive evidence of the existence of the two different stages of 

 consolidation in granitic rocks. Further that while pre-Carboniferous 

 movements had a great influence on Alpine topography, the extent of 

 later elevations can be seen by the foldings of the Mesozoic beds of 

 the Charollaise and the Mayonnaise. It is also contended that the 

 neighbouring granite of Valorcine has altered true gneiss into the 

 schists in which it is intrusive. 



In addition to the woodcuts illustrating the micro-structure of the 

 rocks described, the memoir is accompanied by four admirable photo- 

 graphic views, of which those showing the Mer de Glace opposite 

 the " Angle," and the Aiguille du Chardonnet across the Glaciere 

 d'Argentieres, are especially pleasing. J. W. G. 



BEPOBTS J^ISTJD PEOCEEDIUGS. 



Geological Society of London. 



June 18, 1890.— Dr. A. Geikie, F.R.S., President, in the Chair. 

 — The following communications were read : 



1. " The Borrowdale Plumbago, its Mode of Occurrence and 

 Probable Origin." By J. Postlethwaite, Esq., F.G.S. 



After giving details of the mode of occurrence of the plumbago 

 of Borrowdale in veins traversing diabase and diorite, which 

 break through the Volcanic Series of Borrowdale, the author refers 



