120 SCIENCE IN SHORT CHAPTERS. 



the out-thrust glaciers, the overflow down the valleys, can- 

 not come to an end like the present Swiss and Scandinavian 

 glaciers, by the direct melting action of the sun. They may 

 be somewhat thinned from below by the heat of the earth, 

 and that generated by their own friction on the rocks, but 

 these must be quite inadequate to overcome the perpetual 

 accumulation due to the snow-fall upon their own surface 

 and the vast overflow from the great snow-fields above. 

 They must go on and on, ever increasing, until they meet 

 some new condition of climate or some other powerful 

 agent of dissipation something that can effectively melt 

 them. 



This agent is very near at hand in the case of the Scan- 

 dinavian valleys and those of Scotland. It is the sea. I 

 think I may safely say that the valley glaciers of these 

 countries during the great ice age must have reached the 

 sea, and there have terminated their existence, just as the 

 Antarctic glaciers terminate at the present Antarctic ice- 

 wall. 



What must happen when a glacier is thus thrust out to 

 sea? This question is usually answered by assuming that 

 it slides along the bottom until it reaches such a depth that 

 notation commences and then it breaks off or "calves" as 

 icebergs. This views is strongly expressed by Mr. Geikie 

 (p. 47) when he says that " The seaward portion of an 

 . Arctic glacier cannot by any possibility be floated up with- 

 out sundering its connection with the frozen mass behind. 

 So long as the bulk of the glacier much exceeds the depth 

 of the sea, the ice will of course rest upon the bed of the 

 fjord or bay without being subjected to any strain or tension. 

 But when the glacier creeps outwards to greater depths, 

 then the superior specific gravity of the sea- water will tend 

 to press the ice upward'. That ice, however, is a hard con- 

 tinuous mass, with sufficient cohesion to oppose for a time 

 this pressure, and hence the glacier crawls on to a depth far 

 beyond the point at which, had it been free, it would have 

 risen to the surface and floated. If at this great depth the 

 whole mass of the glacier could be buoyed up without 

 breaking off, it would certainly go to prove that the ice of 

 Arctic regions, unlike ice anywhere else, had the property 



