ON THE STRUCTURE OF GLACIER ICE SOI 



which the proportion of white ice was larger, weathered less deeply 

 and into finer granules. 



The markings of La Brenva, then, are neither ordinary dirt-bands 

 nor direct expressions of structure, nor direct evidence of stratification, 

 but they are produced by the more ready lodgment of dirt in some 

 parts of the superficial layer of the glacier than in others, in conse- 

 quence of the more coarse and deep weathering of these parts ; which 

 again, is the result of the predominance of blue ice over white in these 

 localities. 



Why blue ice should predominate at intervals in the substance of 

 this glacier, — whether the like alternation of structure holds good in 

 glaciers generally, — and whether it has any relation to a primitive 

 stratification, are problems of great interest and well worthy of 

 investigation. 



With regard to the second, I will merely express a belief that 

 some such alternation of structure does obtain in glaciers generally ; 

 for the appearances presented by good sectional views of glaciers, such 

 as that exposed on the north side of the Allalein, are so similar to 

 those exhibited by La Brenva, that I cannot doubt the identity of 

 their cause. I had been in the habit of regarding the appearances 

 referred to as direct evidences of stratification ; but if my supposition 

 be correct they will merely be evidences of an alternation of structure 

 which may or may not depend on stratification. 



