XIV.] THE GEOLOGY OF THE ALPS. 345 



ondary strata upon the schists of the Aiguilles Eouges. These 

 elevated points are evidences of the enormous erosion in this 

 region, the results of which have contributed to build up in the 

 lower regions of the Alps, and in the Jura, the great masses of 

 miocene sediment known as the molasse, a formation partly 

 marine and partly lacustrine, which attains in some parts a 

 thickness of more than 2,000 metres. This period was fol- 

 lowed by other movements which have raised the beds of 

 molasse to a vertical attitude, and in some cases inverted them, 

 so that they appear dipping beneath the nummulitic formation. 

 It is worthy of note that the molasse near Geneva includes in 

 its upper part a lacustrine limestone, followed by marls with 

 gypsum, and by lignites. 



That the nature of the fan-like structure of the Alps is cor- 

 rectly represented in the sections of Studer, Lory, and Favre, 

 can, we think, no longer admit of doubt. Another explana- 

 tion was, however, possible ; the dipping of the beds on either 

 side toward the centre of the mass might indicate synclinal 

 mountains, lying between two eroded anticlinals. Such a 

 mountain- structure appears not to be uncommon in regions 

 where the undulations are moderate ; and is, according to Les- 

 ley, frequent in the anthracite region of Pennsylvania. Snow- 

 don in Wales, according to Sedgwick, and Ben Nevis and Ben 

 Lawers in the Scottish Highlands, according to Murchison, are 

 also examples of this structure, the summits of all of these 

 being composed of newer strata, beneath which, on either side, 

 dip the older formations. When, therefore, geologists of au- 

 thority from Bertrand and Keferstein to Murchison and Lyell 

 maintained that the crystalline rocks of Mont Blanc were 

 newer than the limestones of the valleys on either side, and 

 even declared them to be altered sediments of the tertiary 

 period, it was difficult to regard Mont Blanc as anything else 

 than a synclinal mountain similar in general structure and 

 origin to those just mentioned. Hence it was that in 1860 

 (American Journal of Science (2), XXIX. 118) I remarked, 

 " the weight of evidence now tends to show that the crystal- 

 line nucleus of the Alps, so far from being an extruded mass 

 15* 



