138 Mr. H. H. Howorth on 



"On entering ice caves, etc., underneath glaciers, where 

 ice fills up cavities, the ice appears to enter these 

 cavities not by fracture and regelation, but by change of 

 form, as in the case of a plastic body, for it is remarkably 

 clear and solid looking" {Jour. Geol. Soc.^ XIII. 199). 



Professor Tyndall himself allows that, according to his own 

 view, "it is manifest that the continuity of the fractured sur- 

 faces cannot be completelyand immediately reclosed afterrup- 

 tnre. It is not the same surfaces that are regelated, and hence 

 the coincidence of the surfaces cannot be perfect. They will 

 enclose for a time capillary fissures " {Proceedings Royal 

 Inst.^ 1857, p. 322 note), but the existence of such capillary 

 fissures in the deep ice is absolutely denied by Professor 

 Huxley, who accompanied Professor Tyndall to Switzerland- 

 Professor Huxley's words are: "All deep ice, that is, all ice 

 situated more than a few inches below the surface, is as solid: 

 as glass or marble and as devoid of any but accidental 

 fissures. The glacier, however, where exposed to the 

 atmosphere, presents what may be called ' a superficial 

 layer' of very different character. It is composed of larger 

 or smaller granules of exceedingly irregular form, separated 

 by very obvious fissures, but nevertheless so fitted into one 

 another as to cohese with firmness. The thickness of the 

 superficial layer varies a good deal, seven or eight inches 

 being rather above the average depth. Wherever you clear 

 away this superficial layer you find beneath it what I 

 have termed deep ice, that is, ice in which neither fissures- 

 nor granules are visible." Professor Huxley did not 

 content himself with a microscopic examination of glacier 

 ice, but he tested its porosity by making cavities, some 

 of them with very thin walls, and filling them with 

 coloured liquids, and thus testing its permeability ; and he 

 says, "I can only conclude from these experiments that the 

 chief substance of a glacier is as essentially impermeable as 

 a mass of marble or slate ; and that, though it may be 



