ON THE STRUCTURE OF GLACIER ICE 483 



appeared perfectly smooth and glass}-, exhibiting not the least trace 

 of fissures. Minute shallow pits, however, were scattered over it, 

 and became particularly obvious when a coloured fluid was poured 

 ■on to the surface and then wiped away again, inasmuch as under 

 these circumstances every pit retained a very small portion of the 

 colour. 



The mass was, as usual, traversed by a larger or smaller number 

 of parallel blue veins (whose lenticular form was almost always very 

 apparent, particularly in the Brenva) ; and when a thin section was 

 made perpendicular to the plane of the veins and viewed by transmitted 

 light, it became obvious that the ice formed one continuous mass, 

 without fissures or interruptions of continuity of any kind. It 

 ■contained, however, a multitude of small, closed, and perfectly 

 distinct chambers, and it was to the absence or rarity of these in 

 the course of the veins that the latter owed their transparency and 

 blueness. 



The form and contents of these chambers were exceedingly 

 remarkable. In a blue vein, and in those parts of the intermediate 

 " white ice " which were contiguous to a blue vein, they were always 

 round or oval disks, with extremely flat and closely approximated 

 .sides ; so that, viewed in one plane, they looked like circles ; but in a 

 plane at right angles to this, like narrow parallelograms. In the 

 white ice midway between the blue veins, on the other hand, I very 

 -generally noticed an irregularity of form, which was in many instances 

 so great that the cavities appeared to be ramified. The walls of the 

 ■chambers very frequently appeared to be a little roughened, or, as it 

 ^vere, frosted. 



Every chamber, without exception, which I carefully examined 

 ■contained both water and air. The former was commonly present in 

 larger quantities than the latter, which swam as a bubble in the water, 

 and could very often be made to move about in the chamber like the 

 bubble of a spirit level. It seemed to me, though I will not pretend 

 to lay it down as a rule, that the air was more abundant in proportion 

 to the water in the more irregular chambers. Where the air was in 

 large proportion to the water, the bubble of course became more or 

 less completely supported by the walls of the containing cavity, and to 

 a certain extent assumed its form ; but where, as in the majority of 

 ■cases, the air-bubble was small in proportion to the water, its figure 

 was spheroidal, and totally different from that of the containing 

 -cavity. I mention this particularly, because, as I shall show below, 

 the chambers (which for distinction's sake I will term the " water- 

 f hambers ") have been confounded with the air-bubbles, and the form 



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