192 GLACIAL HISTORY. 



proved by the polishing of the rocky walls and the presence of 

 accumulations of boulders. 



The direction taken by the moraines over this enormous sea 

 of ice has been ascertained by Prof. Guyot, who distinguishes 

 two periods in the history of the glacier. In the first of these 

 its area had its greatest extension, and its subordinate glaciers 

 spread into the high valleys of the Jura belonging to the Can- 

 tons of Vaud and Neuchatel. At this time the terminal 

 moraine was pushed forward as far as Aarwangen and Zofingen. 

 The right lateral moraine stretched along the mountains of 

 Friburg, and was composed chiefly of grey sandstones derived 

 from the sides of the Dent de Morcles (conglomerates of the 

 Val Orcine) ; the left lateral moraine issued from the mountain- 

 mass of Mont Blanc, and conveyed the Alpine granites through 

 the valley of the Trient into the basin of the Rhone ; it may be 

 traced on the side of Savoy as far as Geneva. The central 

 moraines came, in the first place, from the Upper Valais, from 

 which they brought white granites ; secondly, from the masses 

 of Monte Rosa, which furnished the serpentines and eupho- 

 tides ; thirdly, from the head of the valleys of Erinz and Bagne, 

 which sent down enormous masses of talcose granite (arkesine} ; 

 and, fourthly, from the Val Ferret, from which the immense 

 erratics of Monthey are derived. Following the widening of the 

 glacier at its issue from the valley of the Rhone, the interme- 

 diate moraines spread out in a radiating manner, and their 

 materials were conveyed to the slopes of the Jura. In the ter- 

 minal moraines , which extend from Aarwangen to Guggisberg, 

 the rocks are seen in the same sequence : near Guggisberg there 

 are the grey sandstones from the Dent de Morcles, between 

 Schwarzenberg and Konitz the granites of the upper Valais, in 

 the district west of Berne and Burgdorf the rocks of Monte 

 Rosa, near Seebach the talcose granite of the Ering valley, and 

 near Aarwangen the alpine granites of Mont Blanc. . 



In the second period the glacier had become smaller. It filled 

 the basin of the Lake of Geneva, but did not extend so far 

 towards the north-east as in the first period. The left lateral 

 moraine had the blocks from Mont Blanc which had passed 

 through Martigny ; and the right lateral moraine was formed of 

 the grey sandstones and the rock from the upper Valais. The 



