XIV.] THE GEOLOGY OF THE ALPS. 329 



la Savoie," published in 1859. Since that time the views then 

 maintained by Favre have, in spite of much opposition, gained 

 ground, and are set forth at length in the present work, sup- 

 ported by an amount of evidence which seems convincing. 

 We shall endeavor from its pages to present a condensed sum- 

 mary of our present knowledge of the structure of Mont 

 Blanc and the adjacent regions. 



The crystalline rocks of the Alps, as first shown by Studer, 

 do not form a continuous chain, but appear as distinct masses, 

 separated from each other by uncrystalline sedimentary de- 

 posits, generally fossiliferous. According to Desor, there are 

 between Nice and the plains of Hungary not less than thirty- 

 four such areas, standing up like islands from out of the sedi- 

 mentary rocks, and presenting for the most part a fan-like 

 structure (en eventail). Of these masses of crystalline rock, 

 Mont Blanc is the most remarkable, and is described by Elie 

 de Beaumont as " rising through a solution of continuity in the 

 secondary strata, which may be compared to a great button- 

 hole." The length of this area of crystalline rock, measured 

 from the Col du Bonhomme on the southwest to Saxon in the 

 Valais on the northeast, is fifty-nine kilometres, while its 

 breadth, from Chamonix on the northwest to Entreves near 

 Courmayeur on the southeast, is fourteen kilometres. The 

 length of the central mass of protogine is, however, only 

 twenty-seven kilometres. Of the numerous peaks in this 

 area the highest attains an elevation of 4,810 metres above the 

 level of the sea, being 3,760 metres above the valley of 

 Chamonix, and 3,520 metres above the valley of Entreves. 

 This great mass is described by Eavre as supported at the 

 four corners by as many buttresses rising from the surrounding 

 valleys, and known as the Cols de Balme, de Voza, de la 

 Seigne, and de Ferret. The distance between the two valleys 

 just named is only 13,500 metres, and the boldness with 

 which the mountain rises from them is strikingly apparent if 

 we take the Col de 1' Aiguille du Midi and the Col du Geant, 

 which are about 3,460 metres above the sea, and distant from 

 each other 5,000 metres, giving a slope of about 30. A still 



