THE BEDSHIEL KAIMS 309 



We may realise this better by considering the full meaning 

 of a well-known fact that, in the Arctic regions, the Sun's 

 rays have been concentrated by a lens made of pure ice, 

 and paper has actually been lighted at the focus by sunheat 

 that has passed through a frozen mass. Now, the side of 

 the ice-lens facing the object which caught fire melts at a 

 much faster rate than the side of the lens facing the Sun. 

 The difference is due to the difference in the quality (so to 

 speak) of the heat rays from the Sun and those radiated 

 back from the solid body. The one cannot, and the other 

 can, melt ice. This property enables stones or any foreign 

 bodies in, or under, the ice to work their way upward in 

 opposition to the force of gravitation, and, eventually, to 

 rise to the surfuce. It is by these means that stones, mud, 

 and sand (including stones which have become glaciated 

 through onward movement in the sole of the ice) tend to 

 rise into the ice, and to form, as it were, part of the 

 glacier itself. Bodies of this kind, includhuj organic remains, 

 are elevated by means of the factors described into the ice 

 of existing glaciers, and are not confined to the so called 

 moraifie prqfonde. The writer of this note suggested — in 

 The Geological Magazine for November 1874 — that, on 

 investigation, this would prove to be the case, and the 

 prediction has been abundantly verified by several inde- 

 pendent observers since. (See iVahire, October 11th 1897, 

 and Gregory, in the Quarterly Journal of the Geological 

 Society, p. 222, of the volume for 1898.) It was by means 

 such as these that the great ice-sheet of the Glacial Period 

 became charged with rocks, stones, grit, sand, mud, and 

 occasional organisms, which latter, probably in connection 

 with frozen masses of mud, had worked their way up into 

 the ice in the way described. 



At a late period during the Glacial Epoch of the earth's 

 crust here, occurred a depression which eventually brought 

 the glacial conditions to an end. The cause of the depres- 

 sion has been variously interpreted by different students of 

 glacial geology, and it must be confessed that we can 

 by no means be sure as to what is the true explanation. 

 But many persons think that what happened was that the 

 superincumbent load of ice, which had gradually been 



