STUDER — GEOLOGY OF SWITZERLAND. 27 



rocky defile which leads from Cormayeur to the Allee Blanche and 

 the Val Ferret. The view of the Mont Blanc range from this height 

 exceeds in sublimity that from Mont Cramont. Not far from the Mont 

 de la Saxe at the ' Trou des Romains ' can be seen an old mine of 

 argentiferous galena, worked at an unknown period. This is far from 

 being the only mine in the circuit of Mont Blanc, some of which 

 have been abandoned, while others are still in operation : on the 

 heights of Ardon magnetic iron-ore is now being wrought in a talcose 

 schist. 



The "central mass" of the Finsteraarhorn, in spite of its much greater 

 extension and its abnormal direction, presents several rather unex- 

 pected analogies with the two groups just described. The relation 

 of its beds to the upheaved limestone and schist formation is the 

 same as that observed in Savoy, but on a greater scale and more di- 

 stinctly exposed. On the northern boundary of the mass, the most 

 remarkable instances of the contact of crystalline with sedimentary 

 formations occur : the deep ravines have made a clean section through 

 their point of contact, and penetrated into the very heart of the 

 mountain. On the Bach Alp above Leuck, a wedge-shaped mass of 

 gneiss must be regarded as intrusive into the limestone which encircles 

 it. The romantic Gasteren-Thal is admirably calculated for studying 

 such relations. The numerous contortions of the limestone- and schist- 

 beds, as seen on the rocky walls of the Altel and the Doldenhorn, 

 together with the conversion of the lower strata into marble and do- 

 lomite, prove that here, as in Savoy, the limestone is older than the 

 felspathic rocks which underlie it. On the eastern declivity of the 

 Tschingel glacier the granite also appears beneath its covering of lime- 

 stone. Similar conditions may be observed in the Grindelwald, in the 

 deep section of the mountain by which the lower glacier descends. 

 The background of the Urbach valley, and especially the crest of the 

 Urbach Sattel between Tossenhorn and Gstellihorn, also give very in- 

 structive lessons bearing on the same question. The most striking 

 fact is the high inclination of the beds of gneiss which dip to the south. 

 A cursory observation would lead to the belief that the gneiss was 

 older than the limestone, and that its present outline parallel to the 

 beds of the latter was due to the disruption of the mass of both ; but 

 this opinion cannot be maintained if we only cast a glance on the 

 other side of the valley on the mountains of the Laubstock and the 

 Tristenstock. 



The pass of the Grimsel long ago excited Saussure's curiosity by 

 the external characters of the rock. 



The rounded spherical forms {roches moutonnees, rundhocher^ of 

 the gneiss and granite in the valley, and the hummocky and cylin- 

 drical shape of the rocks which hem it in, are seldom seen so marked 

 or so persistent. The contrast between the rounded shape of these 

 rocks and the sharp angles of the high mountain-crests is seldom so 

 distinctly marked as in the chain which surrounds the Aar-Grund on 

 the Grimsel and the glacier of the Vorder-Aar. It requires close ob- 

 servation to satisfy oneself that the rounded bosses really consist of 

 the schistose gneiss which passes uninterruptedly into the upper 



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