154 Proceedings of the Royal Physical Society. 



thick. The ice in the North Sea area certainly must have 

 had its upper surface at a higher level than that of the ice 

 which passed over the watershed, but the difference in elevation 

 need not have been anything like what it has been assumed 

 to be. If, as is here maintained, the movement of glaciers 

 is to a certain extent due partly to the effects of terrestrial 

 radiation, partly to the effects of radiant heat emanating from 

 the Sun, and comparatively little to gravitation, then it 

 would follow that many of the difficulties that have hitherto 

 confronted glacialists in attempting to explain the glacial 

 phenomena of Eastern Britain will be cleared away, and we 

 may turn our attention to other matters which are still 

 under discussion. 



It will therefore be seen from the foregoing statements 

 that gravitation is by no means an essential factor in causing 

 the movement of land-ice. Solar Energy, warming the stones 

 within the lower parts of ice, and warming also the face of 

 the rock next to it, co-operates with terrestrial radiation in 

 elevating the temperature of the ice (more especially if it is 

 thick) to a higher point at its base than it has at the surface. 

 Differential expansion ensues ; the parts of the ice in contact 

 with the rock are warmed most, and, expanding most, are 

 compelled to slide past the rock face, which they do regard- 

 less of both the superincumbent pressure and the enormous 

 friction caused by the grinding of the stone-shod base of the 

 ice over the rock beneath. 



In speculating, therefore, upon the causes which impelled 

 the land-ice of Scandinavia as one continuous stream, from 

 its birthplace to the shores of Britain, we have no need to 

 postulate the existence of land-ice miles in thickness at its 

 starting-point. Solar Energy and terrestrial radiation, co- 

 operating in the manner described, are quite sufficient to 

 account for all the facts, even for the powerful deflection 

 which the Scandinavian ice produced upon the streams of 

 local origin, and even for that remarkable ponding-back of 

 the ice of the North-Western Highlands, which made its 

 upper layers cross the mountain tops, and carry boulders 

 over the watershed westward towards the Atlantic. 



