M. Studer on the Geological Stmcture of the Alps. 147 



able to the direction of the, central mass. On the two sides, 

 tlie beds dip towards the central axis., and their inclination 

 becomes more considerable as we ascend the flanks, until 

 they are completely vertical. The arrangement may be com- 

 pared to a fan, open towards the summit. The rock compos- 

 ing the vertical beds is generally a gneissitic granite, — that is 

 to say, a rock so much approaching to true granite, that we 

 can only see the structure on the great scale, and when we 

 examine it from a distance. In the inclined beds of the 

 flanks, gneiss alternates with other rocks, and we have fre- 

 quently layers several thousand feet thick. Sometimes also 

 the gneissitic granite makes its appearance there as a subor- 

 dinate rock. In ascending the valley of Hash, we see the 

 beds of gneiss and of mica-slate, which form the walls of the 

 valley, dipping to the south as far as above Guttanen, where 

 they give place to a gneissitic granite whose strata gradually 

 become vertical. Near to the Hospice, and at the summit of 

 the Col, the rock has completely the aspect of a true granite ; 

 its beds are vertical ; and it is not until we descend towards 

 Obergestelen, that we see, though in an indistinct manner, 

 the strata dipping to the north. This northern inclination is 

 observable in a more distinct manner at many points of the 

 pass of the Furka, and in the Galenstock, as seen from the 

 summit of the Col of the Grimsel. 



De Saussure, and, after him, Necker, have recognised this 

 fan-shaped structure in the group of Mont Blanc ; Escher de 

 la Linth, sen., observed it in St Gothard ; and, lastly, it is 

 displayed in a striking manner in the beautiful sections which 

 M. Lardy has published of the rocks of St Gothard. 



Flysch, S^c. — The rocks which occupy the space between 

 the different groups are pretty generally distinguished by 

 their regularity. The prevailing rock is the Flysch, that is 

 to say, a grey or black slate, effervescing with acids, often 

 siliceous and passing into a dark-coloured sandstone, and of a 

 large slaty structure ; at other times very calcareous, and so 

 much so, as to deserve the name of calcareous slate. All 

 these varieties of flysch alternate with one another, and somee 

 times contain large calcareous or dolomitic beds, which are 

 frequently accompanied by masses of gypsum. In the Grisons 



