ON THE STRUCTURE OF GLACIER ICE 493' 



frequently observed traversing the middle of the blue veins. At 

 length the fissures extended completely through the mass, which thus, 

 became truly sponge-like. Water poured on its surface, filling the 

 interstices, gave the mass a clear and semitransparent aspect, though 

 by no means to be compared to that of a blue vein. But as soon as 

 the supply of water ceased, the fissures of the side uppermost imme- 

 diately began to lose their water, which drained away below, and 

 becoming filled with air, a whitish opaque hue succeeded. On reversing 

 the block suddenly, what had been its under surface appeared at 

 first clear, but the water soon deserting it, it rapidly whitened, while the 

 previous upper and white surface became clear. Water poured upon 

 the upper surface, traversed the mass and flowed out again below with 

 the utmost ease. In fact it is impossible to conceive any more 

 striking contrast in these respects, than that between the freshly 

 extracted ice-block (or that which had remained under cover) and 

 that which had been exposed. 



So far as it may be permissible to draw a conclusion from the few 

 experiments I made, I should say that direct exposure to the sun has 

 much influence on the rapidity of this process of weathering ; but it is 

 by no means essential, for the northern faces of the walls of crevasses 

 exhibit a well-developed superficial layer ; and I have seen it even 

 beneath huge boulders, where these were not in direct contact with, 

 the ice. 



But one conclusion appears to me to be deducible from these 

 experiments, and that is in perfect accordance with the results of" 

 ocular investigation. Glacier ice is essentially devoid of all pores, 

 fissures and cavities, save the closed water-chambers ; though of 

 course, like all other brittle bodies, it is liable to become fissured and 

 fractured by pressure from without. Fissures and cavities produced 

 in this way, however, are accidental and not essential. But it is a 

 remarkable feature of glacier ice, that it is liable to weather in a 

 peculiar manner, becoming fissured and breaking up into irregular 

 fragments to a certain depth. The superficial layer formed in this 

 way is eminently porous, and absorbs fluids like a sponge. 



In arriving at these results, however, I again regret to find myself 

 in direct opposition to the current doctrine based on the statements 

 of Prof Agassiz, from whose ' Systeme Glaciaire ' I continue my series 

 of quotations. 



(8) " Capillary fissures. — The true capillary fissures are very 

 "different from the superficial fissures which have just been described 

 (3). They exist not merely at the surface, but are found on the walls.. 

 of crevasses and in the interior of cavities where the rays of the sum 



