1846.] GLACIER ICE THE RESULT OF PRESSURE AND COHESION. 201 



The belief which I formerly (in common, probably, with 

 most other persons) entertained, that snow could not pass 

 into pellucid ice without being first melted and then frozen, 

 was part of the chemical prejudice that molecular actions 

 cannot take place except in the liquid state, a prejudice now 

 disappearing, as the subjoined note, on the very competent 

 authority of M. Gay Lussac, shews.* The crystalline forces 

 act on the snowy granules when brought into close contact by 

 pressure, and the imprisoned air is then distributed in the 

 direction of the lines of tearing, in the form of layers of regular 

 globules, just as in the case of the banded lavas which have 

 been so well described by Mr. Darwm.f Bishop Rendu, whom 

 I had the pleasure of visiting at Annecy, remarked a familiar 

 circumstance which illustrates the same thing. We often see, 

 in the coldest weather, that opaque snow is converted into trans- 

 lucent ice by the sliding of boys on its surface ; friction and 

 pressure alone, without the slightest thaw, effect the change, 

 which must take place still more readily in the glacier, where 

 the mass is, during a great part of the year, kept on the very 

 border of thawing, by the ice-cold water which infiltrates it. 

 In this condition, molecular attachment amongst the granules 

 must be comparatively easy, and the opacity disappears in pro- 

 portion as optical contact is attained. Most evidently, also, the 

 icy structure is first induced near the sides of the glacier where 

 the pressure and working of the interior of the ice, accompanied 

 with intense friction, comes into play, and the multitudinous 

 incipient fissures occasioned by the intense strain, are reunited 

 by the simple effects of time and cohesion.:): 



* " II n'est plus permis aujourdhui d'avoir une foi aveugle au principe si banale- 

 ment repete des anciens Chimistes, corpora non agunt nisi soluta. II est certain, 

 au contraire, que tous les corps, solides, liquides, et aeriformes, agissent les uns sur 

 les autres, mais que, des trois etats des corps, 1'etat solide est le moins favorable a 

 1'exercice de I'afnnite." Anndles de Chimieet de Physique, Juin 1846, p. 231. 



f On Volcanic Islands, and in Philosophical Magazine, April 1845. 



| A very remarkable peculiarity is observed in some of the glaciers of Switzer- 

 land, which distinguishes them from the more rapid and precipitous ones of Savoy. 

 The glaciers of the Aar, Rhone, and Great Aletsch, exhibit a degree of crystalline 

 structure which I have nowhere else observed ; broad, laminated, crystalline plates 



