Ixxii PHOCEEDINGS OP THE GEOLOGICAL SOCIETY. 



these mountains, as well as the granitic rock, the protogine, con- 

 stituting the central part of the ridge, are actually stratified ; others 

 consider the divisions to be laminae of foliation ; Mr. Daniel Sharpe 

 took them for planes of cleavage. All except the latter writer were 

 struck with the fan-shaped arrangement of the laminar masses, a 

 structure which is reproduced in the St. Gotthard and other nuclei 

 of the central Alps, as well as in the eastern continuation of the 

 great chain. The sharp needles of rock which lend a special charm 

 to these scenes, and were strangely imagined by De Luc to have 

 been each independently thrust up from the interior of the earth, 

 are but the narrow ends of almost vertical tabular masses, which 

 viewed from the side form serrated ridges, but seen end-on appear 

 to soar as mere isolated points to the sky. 



Close alongside of some of the most marked of these, M. Favre 

 has traced the boundary between the granite and the crystalline 

 schists ; and he adheres to the old statement which has provoked so 

 much discussion, that the schists thus appear to underlie the granite, 

 and as indubitably to overlie the beds of fossiliferous secondary lime- 

 stone*. His own transverse section explanatory of the facts has 

 been before the public for some years, and is the most probable that 

 has yet appeared. The powerful lateral pressure called into action 

 by the upheaval and depression of the chain has produced parallel 

 lines of close flexure, forming a narrow and steep synclinal trough 

 under the valleys on the north and south of the Mont-Blanc mass, 

 and an anticlinal in the main ridge. As the elevation continued, 

 the abutments of the central arch would be squeezed closer together, 

 whilst the upper portion of the great fold of strata was not similarly 

 supported, and would thus tend to bulge, and to throw the beds 

 which were at first the lowermost in order into a position over-; 

 hanging what were the upper. Meanwhile a gigantic denudation 

 must be supposed to have taken place ; and, as M. Favre is fortified 

 by his investigation of that most remarkable outlier of lias and 

 Jurassic strata capping the loftiest peak of the Aiguilles Kouges, 9660 

 feet above the sea, the speculation hardly seems too hazardous that 

 the same band of secondary formations at one time completed its 

 loop above the summit of the whole Mont-Blanc range. 



If a similar reasoning be allowed to hold good for the cretaceous 

 and nummulitic beds, of which there is every probability that they 

 at one time covered the Aiguilles Rouges, and have been subse- 

 quently removed by denudation, it would add to the present height 

 of Mont Blanc a thickness of at least 4100 feet of rock. There 

 would thus have been carried away by denuding agencies from the 

 group (massif) of Mont Blanc alone, and since the comparatively 

 recent epoch of its attaining its full altitude, about 100 cubic miles 

 of solid material. 



Composition of Crystalline Rochs. — M.Favre's frequent excursions 



* The reader may be referred on tliis subject to Gen. Portlock's Anniversary 

 Address to the Society, in 1857, giving figures of the rock-structure and of the 

 excavation carried out by Mr. Euskin near Chr mouni, to settle what appeared 

 to some to be a doubtful question. 



