308 THE BEDSHIBL KAIMS 



Furthermore, the expansion will take place under pressure 

 equivalent to that of the thickness of the ice. So the 

 ice will begin to expand in the direction of least resistance 

 — whichever direction that may be — and will expand most at 

 the greatest depths. Usually the line of least resistance, 

 and therefore of motion, will follow a curve starting from 

 the base of the ice and gradually rising towards the surface, 

 in the direction of the point (which may be many miles 

 off) where the end-pressure diminishes, or where the sheet 

 of ice comes to an end, either by melting, or by breaking 

 off and flowing seawards as icebergs. 



This explanation of the causes of movement of land-ice 

 appears to me to harmonise all the facts I have met with 

 in the course of more than thirty years' study of glacial 

 phenomena, and it possesses the additional merit of explain- 

 ing the movement of land-ice in the maritime parts of 

 Berwickshire and similar places without referring it wholly 

 to the effects of gravitation, and thereby having to assume 

 that the ice in Argyleshire must have been many thousand 

 feet in thickness, and that in Scandinavia many miles. This 

 must have been the case had gravitation alone been the 

 cause which propelled the ice to our shores and produced 

 the observed results. 



There is a closer connection than may at first be thought 

 between the features associated with Eskers or Kaims and 

 the origin of these vast glacial furrows and ridges, for both 

 kaims and drumlins of boulder clay are often moulded over 

 these ridges of rock. But there is yet one point more 

 which needs consideration, on account of its bearing upon 

 the chief object in view. It has already been mentioned 

 that ice is transparent to most of the Sun's rays ; that is 

 to say, pure ice whose temperature happens to be below 

 the freezing point is not much warmed by sunheat. On 

 the other hand, any foreign bodies within the ice (such as 

 may have fallen into the ice down crevasses) warm up undej 

 the influence of solar radiation much faster than ice does, 

 and they warm, furthermore, most on the surface faciug the 

 Sun ; that is to say, on their upper surfaces. Bodies so 

 warmed possess the property, which the direct rays of tie 

 Sun do not possess, of melting the ice in contact with theaa. 



