real Hliucture of Glacier la. 13D 



Extract Fifth. — Mr Rohcrtson of Newton to Professor Forbes, 



Newtox, 4th M(ty 1842. 



" Before joining you on the 13th August last year, I was pretty familiar, 

 from reading, with all the ordinary phenomena of glaciers, and, on my 

 walk to the ' Cabunc,' examined each as it presented itself. Among others 

 I observed the supcrfckil'mAicnilons of the ribboned structure ; and, dur- 

 ing the first half hour after my arrival, I recollect perfectly, in walking 

 from the ' Crevasse ' at the end of the Finster Aar glacier (where you had 

 been preparing the experiment on the absorption of ice with red wine) to 

 the left flank of the Lauter Aar (where we exposed, Avith a hatchet, the 

 contact of the ice and rock, in order to see the sand, &c. between them), 

 having asked Agassiz how it was produced ? He told me that the sur- 

 face of the glacier had completely changed since !ast year, when he had 

 scarcely observed it, — that it was an effect of the moraines, and probably 

 caused by the greater variations of temperature to which they were sub- 

 ject as compared to the rest of the glacier, and that it had nothing to do 

 with stratification. I remember also asking whether the horizontal lines 

 at the end of the glacier were those of stratification .'' and was told ' un- 

 doubtedly.' 



"On our return to the ' Cabane,' I pointed out the structure very well 

 marked, at some distance from the moraines, and, on cross questioning 

 Agassiz, saw that he was far from satisfied with his theory. 



" I have thus abundant evidence, independent of your ample testimon}', 

 to shew, that, at the date I have mentioned, my friend Agassiz was un- 

 aware of the general occurrence of the ribboned structure, through the 

 mass of glaciers ; and, in writing to him some days ago, mentioiicd my 

 conviction that the discovery^ certainly the most important of tlie recent 

 ones, was due to you. I shall be glad to find that, as I believe is the 

 case, j\I. Desor alone, and not M. Agassiz, could call it in question." 



The " stratification'' alluded to at the close of the first pa- 

 ragraph of tlie preceding letter, refers to the twisted planes of 

 structure v^•hieh I have described in my paper, and which are, 

 in fact, continuous with the veins which, throughout the 

 greater mass of the glacier, run parallel to its sides, when 

 these sides are steep and continuous. The complex form of 

 the surfaces of the shells into which a glacier is divided by 

 these bands of compact and friable ice, I was first able to dis- 

 cover, during a visit to the glacier of the Rhone on the 23d 

 August 1842. I was accompanied by Mr Heath, and Mr Cal- 

 verley Trevelyan, but not by M. Agassiz or any of his party. 

 In the course of a very careful examination of the glacier, I 

 succeeded in satisfying myself completely of the conoidal I'orni 

 of the veined surface, and in ex})laining the apparent frontal 



