484 ON THE STRUCTURE OF GLACIER ICE 



which is characteristic of the one has been erroneously ascribed to the 

 other. 



I had no means of measuring the dimensions of the water- 

 chambers, but at a guess I should say they varied from a tenth to a 

 fiftieth or a sixtieth of an inch in diameter. 



The line of contact of the water in the water-chambers with the 

 ice was optically perfectly well defined, and easily distinguishable.. 

 Hence I have no hesitation in saying, that if canals or fissures of any 

 appreciable size filled with water had existed in the ice, I must, with 

 the magnifying power employed, have discovered some trace of 

 them ; but I repeat, nothing of the kind was discernible in perfectly 

 fresh ice. 



If the existence of fluid water dispersed through its substance in 

 closed chambers is shown by future observations to be a universal' 

 character of glacier ice (and I cannot imagine that a structure 

 universally prevalent in the Mer de Glace, the Geant, the Brenva,, 

 and, as I shall show by-and-bye, from M. Agassiz's figures, in the 

 Aar glacier also, is a mere local peculiarity), it appears to me to be 

 a fact of primary importance. For what I have described is the 

 structure of the unchanged ice of the glacier — of ice which has been 

 protected from the solar or atmospheric influences by that which 

 covered it ; and it must be remembered that the ice which is within 

 a foot of the surface on the Mer de Glace opposite the Montanvert,, 

 must have formed a part of the very depths of the tributary glaciers.. 

 In other words, the ice which is at this moment, say a hundred feet 

 below the surface in the Glacier du Geant, will, in consequence of 

 ablation, form the superficial ice of some part of the Mer de Glace years 

 hence. Consequently, unless it can be shown that the substance of 

 a glacier, as it approaches the surface, is exposed to some influences 

 capable of developing the water-chambers and their contents, it is to- 

 be presumed that the structure found near the surface in the lower part 

 of a glacier is the structure which prevails throughout the thickness, 

 of the higher part ; and hence that the structure described is that 

 of unaltered glacier ice in general. This conclusion, as I shall 

 immediately show, is directly confirmed by the boring experiments, 

 and by the figures of M. Agassiz. 



M. Agassiz's deductions, however, are totally at variance with 

 mine ; and he is so generally quoted as an authority in these matters,, 

 that I feel compelled, however unwillingly, to enter into a detailed 

 criticism of his views, which are contained in the following extracts 

 from his ' Systeme Glaciaire,' numbered, for the sake of more con- 

 venient reference, in successive order. 



