xxii RECENT PROGRESS OF THE GLACIER THEORY. 



being first melted and then frozen. Friction and pressure alone 

 I affirmed to effect the change, especially in the glacier, 

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

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

 this condition, molecular attachment I stated to be comparatively 

 easy, the opacity disappearing as optical contact is attained. 

 The " glacification" of the neve takes place by the kneading or 

 working of the parts under intense pressure,^and the multitu- 

 dinous incipient fissures are reunited by the simple effects of 

 time and cohesion. Thus the conversion into ice is simultaneous, 

 and in this case identical with the formation of the blue bands, 

 which are formed where the pressure is most intense, and 

 where the differential motion is a maximum, that is, near the 

 walls of the glacier. * 



Thus the whole phenomena of the transformation of the 

 glacier from fresh fallen snow into laminated cohering ice, 

 which constitutes the character of the true glacial substance, 

 even at great depths, were accounted for without the embar- 

 rassing admission of the penetration of the winter frosts to an 

 unlimited extent, f 



It was important that I should specifically point out this 

 change in my opinion, of which the record is to be found in these 

 pages, because it is the only one (I hope) which occasions a 

 discrepancy of any consequence between my earlier and later 



* These expressions are verbally taken from the Thirteenth Letter, pp. 200, 201. 



f Since a certain amount of congelation of infiltrated water must necessarily 

 take place during winter, at least near the surface of a glacier, it is easy to see 

 that it is a matter of nice discrimination to limit precisely its agency in a theory of 

 glaciers. Certain phenomena cannot be produced without it. Such are the lenti- 

 cular frozen cavities which were described by myself on the Glacier of Bossons, and 

 which have been since particularly noticed by Messrs. Tyndall and Huxley, and by 

 Mr. Ball. I have referred to them more than once in the papers printed in this 

 volume, where I have described them as the limit of the veined structure when the 

 dislocating forces are very great and the lateral compression small, and I have also 



