548 THE LIFE OF JAMES D. FORBES. [APPEND. 



EXTRACT SECOND. Professor Agassiz to Professor Forbes, 29th March, 1842. 



' Comme vous en convenez vous-meme lorsque nous discutames pour la 

 premiere fois les bandes de glace de teintes diverses que Ton observe dans le 

 glacier, je, vous dis que fen avals remarque, DES TRACES SUPERFICIELLES au 

 Glacier des Bois en 1838, ce qui est mentionne^ians mon livre p. 121, a 1'occa- 

 sion des moraines medianes.' 



It appears, then, that Mr Heath's memory and my own agree 

 thus far precisely with M. Agassiz. Let us see whether the 

 reference to the 'Etudes sur les Glaciers/ published in 1840, 

 gives any farther evidence. 



EXTRACT THIRD. Agassiz, l Etiides sur les Glaciers,' pp. 121-2. 



' Les trainees regulieres et paralleles de grains de sable que Ton poursuit 

 quelquefois sur de tres grandes etendues, le long des moraines medicines, me 

 paraissent etre un effet de la dilatation de la surface charged de debris, combine 

 avec le mouvement progressif de toute la masse. Les pctits grains de sable 

 6pars, n'agissant pas comme les gros blocs, 1 teudent a former des series (Qu. 

 stries ?) longitudiuales et paralleles qui se transformed quelquefois en rainures, et 

 qui servent meme souvent de lit aux petits filets d'eau qui coulent le lor. 

 moraines. Nulle part je n'ai observe ce phe"noinene d'une maniere 

 frappaute que sur la Mer de Glace de Chamonix en 1838 ; je 1'ai egalement 

 remarque sur le Glacier de 1'Aar, et ce qui ni'a confirme dans 1'explication que 

 j'en donne, c'est qu'ici on remarque sur le cote gauche de la grande moraine une 

 petite moraine qui lui est parallele, et qui me parait d^tache'e de la n 

 maniere que les trainees de sable dont je viens de parler se de"tachent des 

 moraines en general.' 



It appears then, that, after three years of observation of the 

 glaciers, M. Agassiz still entertained, in 1841, the same view 

 of the cause of a fact which he had observed in 1838, and pub- 

 lished in 1840. The fact was the superficial arrangement of 

 lines of sand near the moraines of glaciers, which, according 

 to him, arose from some molecular dilatation of the ice, which 

 he does not very clearly explain ; and its effect was sometimes 

 to produce grooves (rainures}, by the heat of the sun acting on 

 the sand thus arranged. 



The fact which 1 pointed out to him on the 9th of August 

 had no reference to the arrangement of sand on the ice, but 

 consisted in a texture which the ice itself presented through- 

 out its mass, of harder and softer layers, whose wasting, when 

 it occurred in the neighbourhood of the moraines where the 

 glacier was covered with sand, occasioned hollow grooves, into 

 which, for obvious reasons, the sand was speedily washed, and 

 there it lay. M. Agassiz was very naturally and properly slow 

 to admit, in explanation of a fact which had for three years 

 been before his eyes, the existence of a prevalent structure to 



1 This refers to the well-known action of large blocks of stone in defending 

 the surface of the ice from evaporation ; here, on the other hand, the sand suni 

 in the ice. 



