377 



that this variety of stratification had not been recognized as a dis- 

 tinct form, but had been confounded with the horizontal stratifica- 

 tion. He stated that this form would only be met with when the 

 original structure of the glacier had been broken up and destroyed 

 by some obstructing barrier or other cause. He instanced as the 

 most marked example of this the terminal portion of the Rhone 

 glacier, after it pours into the valley of the Rhone over its rocky 

 barrier or precipice. He described the strata as being formed close 

 to the icy mass on which the icy cataract descends, originally paral- 

 lel to each other, and with a dip of 70° ; but that, as new layers 

 are formed, and the first formed layers are pushed forwards, they 

 lose their parallelism to each other, and assume angles of dip less 

 and less as they approach the termination of the glacier. This 

 change of dip and of parallelism the author attributed to the for- 

 ward movement and plasticity of the mass, together with the greater 

 amount of friction below, where the ends of the layers were in con- 

 tact with the ground, and the constant deprivation of support ante- 

 riorly and below, from the continued melting of the ice at these parts, 

 which would give the layers a constant tendency to fall forwards. 



The author then proceeded to shew that fissures or crevices in 

 glaciers could not bo produced in consequence of the unequal expan- 

 sion of the ice itself, nor in consequence of the expansion of the air 

 contained within its pores ; but that in every case crevices were pro- 

 duced in censequence of the movement of the glacier over the in- 

 clined plane on which it rested. 



The author next passed to the second division of his subject, the 

 Movement of Glaciers, and first commented on the Dilatation Theory. 

 He endeavoured to prove that none of the phenomena observed in 

 glaciers could be accounted for by that theory. That a glacier was 

 not retarded in its movement though riddled with crevices ; that 

 the supposed dilatation did not alter the form of the walls of these 

 crevices ; that it did not close them at their upper extremity nor 

 widen them out below ; that it did not give rise to any convexity of 

 the surface of the glacier ; that the icy mass did not require to touch 

 the rocky walls of the valley through which it passed ; that it could 

 move onwards for miles quite unsupported on its margins ; that du- 

 ring a whole summer, whilst its movement was greatest, it never 

 dilated even the few feet requisite to fill up the spaces intervening 

 between its margin and the rocky walls of the valley ; that it ad- 

 vanced during the heat of the day, and during winter, when it is al- 



