DE SAUSSURE IN SCIENCE AND LITERATURE 429 



(about fifteen English) feet. He adds that some Englishmen had 

 applied the same test with heaps of stones and had got a like re- 

 sult. These rough attempts probably formed the basis of a corre- 

 sponding statement in Ebel's Guide (1793), severely commented on 

 by Forbes, whose own observations gave the yearly motion at the 

 same spot as 482 feet ! It is curious to find that Forbes' measure- 

 ment had been anticipated by an observation recorded in the 

 work of a Genevese pastor published in 1817. l A boulder that had 

 fallen from the Dru on to the glacier had moved eighty and a half 

 toises in eleven months at a rate, that is, of about 520 feet in 

 the year. 2 Again, it is strange to find that de Saussure believed 

 that the middle of the glacial surface advances more slowly than 

 its sides ; although the dirt -bands, visibly convex towards the 

 lower end of the glacier, serve to prove the contrary. Once more, 

 the origin of medial moraines from the meeting of inner lateral 

 moraines where two ice-streams join is nowadays generally recog- 

 nised even by an average peasant. I can only endorse with regret 

 the comment of Forbes on de Saussure 's treatment of this feature : 

 * There is nothing more surprising to be found in his writings 

 than the most unsatisfactory explanation which he gives of 

 medial moraines.' It is fair to quote the passage (Voyages, 537) 

 which called forth this severe comment. I have slightly abbre- 

 viated it : 



' In the heat of summer, streams, formed by the melting of the ice, 

 flow on the surface of the glacier and crevasses open, and as the 

 trough of the glacier has the form of a cradle, the ice in the middle 

 shrinks and falls, while the stones on the sides of the glacier [the 

 outer lateral moraines] slide away from the mountain towards its centre. 

 The accuracy of this statement is shown by the fact that towards the 

 end of summer one sees frequently, and particularly in the larger 

 valleys, a considerable gap between the foot of the mountain and the 

 edge of the glacier, and these gaps arise not only from the melting 

 of the glacier's edges, but also from their having shrunk away from 

 the mountain in falling towards the centre of the glacial trough. 



1 Promenades Philosophiques et Religieitses aux Environs du Mont-Blanc, 

 Geneva and Paris, 1817. 



2 In the eighties of the eighteenth century the Chamonix glaciers were 

 on the increase. Of the Glacier des Bois Mr. Brand, in a manuscript diary of a 

 tour in 1786, writes : ' It was really curious to see the green tops of larches 

 which the glacier had borne down by its pressure showing themselves amongst 

 the fragments of ice and granite.' 



