398 PKOCEEDINGS OP THE GEOLOGICAL SOCIETY. [April 9, 



are detached from the great Alpine groups. The Matterhorn, the 

 Grivola, the Viso, the needle of Bessans, that of Mondrone, &c. are 

 all or partly composed of these rocks. Mont Blanc and Monte Bosa 

 are colossal masses, while the others are isolated points produced by 

 the fall of their flanks. These dioritic, serpentine, and euphotide 

 rocks are in no wise eruptive. I have followed them for more than 

 100 kilometres from the valley of the Toce to that of Chisone and 

 the Po ; and I have seen that they are disposed in zones, hands, and 

 ribboned layers, which surround the masses of ancient gneiss. 

 Thus the Viso, which, according to M. de Beaumont, is a centre of 

 elevation, is to me only a euphotide layer which has resisted 

 atmospheric degradation, of which the flanks, weatherworn and 

 decayed by rockfalls, now make one of the most beautiful pyramids 

 of our Alps. 



These amphiboHtes, euphotides, and serpentines not only appear 

 in the Alps, but at many other points on the surface of the globe, 

 covering more ancient crystalline rocks, and are in their turn 

 covered by various palaeozoic formations. In the Alps of Lombardy 

 and Venetia the zones of serpentine, diorite, and greenstone are 

 found near the centre of the chain running east ; but on leaving the 

 St. Gothard they describe a curve and strike towards the south. 

 Thus in Piedmont the diorites, amphiboHtes, euphotides, and ser- 

 pentines form the outer band of the Alps towards their base on the 

 border of the plain, and are directly covered by the Pliocene and 

 alluvial strata. The large dioritic band, which in the valley of the 

 Toce is found above and outside the basin of the Lago Maggiore, 

 forms the zone by which the valley of the Baltea debouches at 

 Ivrea ; and it is the zone of amphibolite, euphotide, diorite, and 

 serpentine which forms the country at the mouth of the Dora 

 Biparia on its passage to the plain of the Po. This is the reason 

 why the mouths of these two valleys are so narrow. The glaciers 

 of the Adige, of the Ticino, and of the Toce, in debouching into the 

 valley of the Po, have easily eroded the granite (one proof of which 

 is the separation of Mount Orfano from Baveno), mica-schist, lime- 

 stone, gneiss, &c, and have hollowed large and. deep basins. The 

 glaciers of Baltea and Biparia at their opening into the plain met 

 with a large zone of diorite, euphotide, and serpentine, which 

 obliged them to rise, and which resisted their erosive force and 

 consequently the excavation of large and deep basins. I have, 

 however, long been convinced that near Ivrea and Avigliana, in the 

 interior of the two morainic amphitheatres, there was a shallow 

 lake, which is now completely filled, between Avigliana and Bivoli, 

 but which at the Val d'lvrea still leaves open the two lacustrine 

 basins of Candia and of Viverone. The bottom of these amphitheatres 

 shows no erratic blocks, because they are covered by the alluvium 

 which has filled the lake. The opening of the valley Stura di Lanzo 

 is also barred by a great band of euphotide and serpentine ; but here 

 the glacier did not pass out beyond the valley. However, the water 

 that flowed from the end of the glacier (the foot of which I did not 

 find for some kilometres up the valley), impetuously rushing agaii st 



