72 REV. A. IRVING ON THE 



different degrees of hardness, and that thus rock-basins might have 

 been produced. 



Mr. Walter Browne agreed with previous speakers that the 

 fact that the rivers flowing from the ends of glaciers contain so 

 much mud is proof positive that they erode their beds. He had 

 seen the Gbrner glacier pushing the turf of fields before it like a 

 plough. He called attention to considerations laid before the Royal 

 Society in his recent paper, especially that the Greenland glaciers 

 move, in the depth of winter, at temperatures far below 0° C. ; and 

 he thought this fatal to the movement of glaciers being due to rege- 

 lation. According to the author's theory, glaciers would cease to 

 move when they reach a horizontal surface. 



Dr. Hicks thought that the author had proved his case, which 

 was, that ice, by itself, cannot erode rock- surfaces. 



Dr. Woodward referred to the observations of Dr. Hector, in 

 New Zealand, and said that no glaciers are absolutely clean, but all 

 contain rock fragments, consequently all glaciers are capable of 

 erosive action. 



Mr. Batterman objected to the author's comparison of ice and glass. 

 Ice is perfectly crystalline, as shown when examined by polarized 

 light, the principal axis of the crystals being perpendicular to the 

 planes of cooling. Apart from this point, he was inclined to agree 

 with the conclusions of the author. He did not think there were 

 any experiments which could be quoted in support of the view that 

 glaciers can erode rock-basins. He thought that what is usually 

 called glacier-erosion would be found to be due to the erosion of 

 water in confined channels beneath the glacier. 



The Eev. E. Hill said that the argument that the thrust was 

 mainly expended in overcoming cohesion rather told against the 

 author's views than supported them, as the friction of the sides of the 

 glacier is necessary to produce a resistance to the thrust. 



The Eev. E. S. Dewicz agreed with Mr. Bauerman's views on the 

 subject. 



The Author said that, in the remarks objected to by Mr. Hill, he 

 had been merely arguing against the view that the glacier moves as 

 a solid mass. He fully recognized the " filing " action of the stones 

 held in the ice ; but since these stones and the rocks they grind 

 against are of equal hardness, only at most one half of the pulverized 

 material brought away by the glacier-stream comes from the rocks 

 over which the glacier moves. He agreed with Mr. Bauerman as to 

 the work done by streams beneath the glacier, and had given an 

 illustration of it in the paper. He argued, not against the erosive 

 power of glaciers, but against their power of cutting rock-basins such 

 as those occupied by lakes. He had already met many of the objec- 

 tions raised to his views in a paper to be read in a fortnight's time. 

 He had pointed out one cause of the motion of glaciers which is 

 quite independent of climatal conditions, namely the conduction of 

 heat to the glacier from below. The surface- conditions in a region 

 of excessive radiation like Siberia, which Mr. Browne had referred 

 to, were not comparable with the conditions found beneath the 

 glaciers in Greenland. 



