CONSOLIDATION BY FRICTION AND PRESSURE. XX 



effects of differential motion in developing the veined structure, 

 it is added, " I believe that it is during the progress of the glacier 

 thus subjected to a new and peculiar set of forces depending on 

 gravity, and which remodel its internal constitution by substi- 

 tuting hard blue ice in the form of veins for its previous snowy 

 texture, that the horizontal stratification observed in the higher 

 part of the glacier or ntoe is gradually obliterated."* It will 

 be seen in the pages of this volume that the identity of the 

 process which (at least in the higher glacier) produces the blue 

 veins of the ribboned structure, with the conversion of granular 

 snow into glassy ice, remained for nearly three years a strongly 

 fixed idea in my mind, but it only received a satisfactory 

 development when I returned to Chamouni in 1846, thoroughly 

 unsatisfied with the explanation of the conversion of the ntve 

 into ice by thaw and congelation, and determined, if possible, 

 to find a better solution for it. In the meantime I avoided in 

 my writings any farther allusion to the mode of this conversion, 

 as to which I had merely sanctioned the traditional opinions 

 adopted even by De Saussure, notwithstanding his well-founded 

 objections to the dilatation theory. f 



But in my autumn journey of 1846 this difficulty was 

 removed, and I hastened, on my return, to record in my 

 Thirteenth Letter on Glaciers! my now clear conviction that 

 all the phases of consolidation of a glacier are due to the effects 

 of time and cohesion alone acting on a substance softened by 

 the imminent approach of the thawing state, in opposition to 

 the belief which I formerly, in common with most other persons, 

 entertained, that snow could not pass into pellucid ice without 



* Fifth Letter, p. 53 of this volume. 



f " Ces memes neiges . . . abreuvees des eaux des pluies et des neiges fondus, 

 se gelent pendant I'hiver, et forment ces glaces poreuses dont les glaciers sont com- 

 poses." Voyages, torn. i. 527. 



| Reprinted in the present volume, page 199. 



