OE THE OUTER HEBRIDES. 869 



and down hill, as the advocates of an ice-sheet required it to do. 

 If Gree aland, as had been asserted, was covered with an ice-sheet, 

 surely this would be able to cross the narrow strait separating that 

 country from the American continent ; but it appeared that Green- 

 land really had only enormous glaciers, which did not cross the 

 strait. We can, indeed, theorize as to the conditions prevailing in 

 the Antarctic region, because we know little or nothing about 

 them ; still it was to be observed that, while the Arctic icebergs are 

 very irregular in form, the Antarctic ones are flat-topped. The 

 former are fragments of glaciers, hence their form ; the latter had 

 not been strained, and so showed that they were not derived from a 

 sheet moving over the southern continent. He doubted whether 

 there was any physical evidence to prove that ice could move to the 

 extent required on a slope of 1 in 211, or indeed of 1 in 422 ; in 

 such a case he regarded it as impossible that gravitation could 

 produce motion. The absence of fragments from the mainland and 

 Inner Hebrides upon the Outer Hebrides seemed to him to show 

 that no great body of ice could have passed from the former to the 

 latter. The formation of Boulder-clay was probably effected in 

 shallow water by floating ice. 



Prof. Eamsat thought that the idea of local precipitation favouring 

 glacial action, though not new, had been remarkably well treated by 

 Mr. Jamieson. The notion of the existence of two great ice-sheets, 

 once put forward by Agassiz, would not, he thought, be again 

 seriously advanced. At the same time, he did not think that 

 floating ice and comparatively small glaciers would explain the 

 phenomena recorded by Mr. Geikie along all the western side of 

 Scotland above the sea and below it. In his opinion, glacier ice did 

 not move by gravitation alone ; its behaviour was, so to speak, more 

 like that of sluggish water. The marks, as a rule, follow the general 

 trend of the valleys, though there might be local variations, and the 

 direction of glaciers could be inferred from the markings. Jle 

 thought that there was good evidence that large districts of Scot- 

 land, England, and Ireland had been covered by land-ice, and he 

 quite accepted Mr. Geikie's conclusions as to the thickness of the 

 ice. He had himself found it 1300 feet in the Llanberis valley. 

 He called attention to the rock-basins between the mainland and the 

 Hebrides being just where his theory of excavation would require 

 them to be, paralleling the case of the lakes in the Alps and at the 

 foot of the Jura. If a great quantity of ice accumulated in the 

 interior of a district it would flow outwards. 



Prof. Judd stated that, while boulders derived from Skye, Rum, 

 Mull, &c, did not go to the Outer Hebrides, and on Skye rocks 

 from the mainland are very rare, yet boulders derived from the 

 Inner Hebrides are certainly found on the west coast of Scotland. 



Mr. Callard remarked that, if Mr. Croll's theory were true, we 

 ought to find evidence of the glaciation of the planet Mars at the 

 present time. But such was not the case, so he doubted the 

 correctness of the theory. Referring to the President's remarks, he 



