126 



strong one in favor of his theory ; for it was quite natural to sup- 

 pose that this would be the case, since the ice at this point had 

 not been exposed to the influence acting upon it long enough to 

 produce the structure in question. He regarded Prof. Forbes's 

 opinion that the ribbon ice is caused by a movement of the mass 

 on itself, by which longhudinal fissures are formed, as unphilo- 

 sophical; since it would suppose a cohesiveness among the par- 

 ticles, and a disposition to separate into planes parallel to its 

 course, not in accordance with the laws of such a mass. The 

 fissures spoken of by Mr. Desor he regarded as the effect of 

 atmospheric erosion, like those in a slate quarry. The bands 

 could not be caused by water freezing in cracks of the glacier, 

 as such ice would be likely to have an irregular, crystalline 

 arrangement, as is seen where cracks in pond ice have been 

 closed up. 



Dr. Jackson asked Mr. Desor if he knew M. Elie de Beau- 

 mont's opinions on the structure under consideration. 



Mr. Desor replied that M. de Beaumont admitted the constant 

 correlation between the fissures and the bands, and attributed the 

 former to a shrinking in winter. 



Dr. Jackson said it did not seem to him important that the fis- 

 sures should penetrate the whole mass. The contraction would 

 be the greatest on the sides where the glacier is the thinnest, and 

 where these bands of ice are found. 



Mr. Desor remarked that it had been ascertained that below a 

 depth of about ten feet, the centigrade thermometer stands inva- 

 riably at zero. 



Dr. Jackson replied that he did not attach much importance to 

 this fact, since if the surface were to contract, the fissure would 

 extend downwards to a depth proportionate to the toughness of 

 the ice, and on the sides this process would go on the easiest. 



Prof. Rogers said, that if fissures, ultimately giving rise to the 

 bands in question, were thus formed by radiation from the bar- 

 rier mountains or the direct rays of the sun, they would neces- 

 sarily occur on the side of the glacier most exposed to these 

 influences, and in accordance with the direction of the glacier. 

 This was not found to be the case. In fact, none of these me- 



