XIV.] THE GEOLOGY OF THE ALPS. 343 



that the underlying crystalline rocks, forced by great lateral 

 pressure, formed an elevated anticlinal arch, which, breaking on 

 the crown, from the excess of curvature, shows the lowest rocks 

 in the centre of the rupture, flanked on either side by the over- 

 lying strata. These, in their upper part, are subjected to a 

 comparatively feeble lateral pressure, while the deeper portions 

 are forcibly compressed by the smaller folds on either side, from 

 which results the fan- like or sheaf-like structure of the mass. 

 The newer strata in the synclinals are by this process arranged 

 in troughs, and are more or less overlaid by the older rocks. 

 Such a synclinal exists in the valley of Chamonix, between 

 the two ruptured and eroded anticlinals represented by Mont 

 Blanc and the Brevent. In illustration of this structure Favre 

 has given a grand section commencing to the northwest in the 

 mountain known as Les Fiz, which, overlooking the Col d'An- 

 terne, rises to a height of 3,180 metres, and displays all the 

 Alpine formations from the sandstones of Taviglionaz, overlying 

 the nummulitic beds, down to the carboniferous, which i is seen 

 resting on the crystalline schists. These appear in the height 

 of Pormenaz, and in the Brevent, at the northwest base of 

 which the carboniferous rocks are arranged in a sharp fold dip- 

 ping beneath the crystalline strata. The latter, to the northeast, 

 rise in the Aiguilles Eouges, which are steep hills of vertical 

 beds including hornblendic, chloritic, and talcose rocks, with 

 petrosilex, eclogite, and serpentine. The highest of the Ai- 

 guilles rises 2,944 metres above the sea, and consequently 1,892 

 metres above the valley of Chamonix. This summit, which 

 was visited by Favre, was found to be capped by horizontal 

 strata, consisting at the top of about thirty-seven metres of Ju- 

 rassic beds, with belemnites and ammonites, underlaid by infra- 

 liassic strata with cargneules, sandstones, and schists, the whole 

 resting upon vertical strata of unctuous mica- schists, which 

 enclosed a bed of saccharoidal limestone. From thence we pass 

 over the valley of Chamonix, which holds enfolded in crys- 

 talline schists triassic and Jurassic strata, and over the summit 

 of Mont Blanc, to find the same folding repeated between the 

 base of the latter and the protogines of Mont Chetif. The fan- 



