160 M. Studer 07i the Geological Structure of the Alps. 



western Switzerland, at the foot of the Alpine Jura. The 

 pebbles of which it is there composed, are, as in the Rigi and 

 in eastern Switzerland, essentially limestones and sandstones, 

 which correspond with the nearest rocks of the Alps ; never- 

 theless there are also mixed with these, granites and other 

 rocks whose origin is unknown. 



In the nagelflues of the canton of Berne, which form several 

 chains of hills whose beds dip, sometimes to the south, some- 

 times to the north, it is these rolled masses, foreign to the 

 Alps, which predominate ; in the nagelflue of environs of 

 Thoune, Avhose beds dip to the south, we find, in particular, 

 red porphyries and granites of all kinds, such as occur in the 

 great porphyry chains. Similar rocks present -themselves in 

 the Black Forest, and at the southern base of the Alps. Near 

 Thoune, another kind of pebbles is mixed with these rocks, and 

 predominates especially in the nagelflue of the Belpberg, and 

 of the Emmenthal, which is horizontal or has a northern in- 

 clination. These are fragments of serpentine and gabbro, 

 rocks which only exist In situ, so far as we know, in the south- 

 ern part of the Grisons, also of compact serpentines contain- 

 ing diallage, several other species of gabbro, granites, green 

 porphyries, green or violet-coloured slates, and aphanites. 

 The Emmenthal likewise contains spilites or amygdaloidal 

 rocks, and variolites. In a small district to the north of the 

 Emmenthal, pebbles of quartz and the debris of a hornblendic 

 rock predominate. The sand brought down by the torrents 

 of this district contains grains of gold with much magnetic 

 iron, garnets, and other minerals. Where are we to seek for 

 the beds of porphyry, of serpentine, and of auriferous horn- 

 blende, which have furnished those enormous quantities of 

 rolled stones ? In what manner, and by what agent, have these 

 pebbles been accumulated at the base of the Alps, in masses 

 sufficiently large to appear considerable even in the vicinity 

 of those elevated summits ? These problems are still unsolved. 

 To suppose that the pebbles have come from the interior of 

 the earth, and that their considerable masses, produced during 

 the long period which corresponds to the last convulsions of 

 the Alpine system, cover the beds whence they were derived, 

 or that these very beds are partly destroyed, is too arbitrary 



