146 Proceedings of the Royal Physical Society. 



except the southern part of England, was swathed in 

 one vast mantle of ice. 



Another question now arises : How came it that these 

 vast confluent sheets of ice radiated to so great a distance 

 from their centres of dispersal ? So far as Scotland is con- 

 cerned, there are many reasons for believing that these 

 centres of ice-dispersal coincided, nearly, but not quite, with 

 the centres of the areas where there is the greatest winter 

 rainfall now. A line passing through these centres does not 

 coincide with the watershed, but lies to the east of it in the 

 districts north of Glen More, and to the west of it on the 

 south of that line of depression. A similar line marked the 

 direction of the main axis of dispersal of the ice during the 

 Glacial Period. The movement of at least the higher parts 

 of the ice in the north-west Highlands of Scotland com- 

 menced, at the climax of the Glacial Period, on the eastern 

 slopes of the mountains (for a reason which we shall 

 presently consider), and was continued westward up their 

 slopes and over their summits in the direction of the 

 Atlantic. It is possible that this westward movement may 

 have extended to the middle or even to the lower strata 

 of the ice. In the south-east Highlands, the line of ice-shed 

 extended through the Cairngorms, south-westward across 

 the main watershed, and then southward, keeping some 

 distance to the west of that line ; so that the branch of the 

 ice-sheet that filled the basin of the Forth originated in the 

 mountains of Argyllshire, far to the west of the head- waters 

 of any branches of the Forth. The feeders of the ice of the 

 Forth basin, therefore, must also have travelled uphill over 

 part of their course. AVhy they did so is difficult to explain 

 satisfactorily on any theory that has yet been put forward. 

 The difficulty is increased when we consider the now well- 

 known fact that a continuous mass of solid land-ice extended 

 from the mountains of Scandinavia across what is now the 

 North Sea, and well on to what are now the maritime parts 

 of eastern Scotland. What was the nature of the agent that 

 forced extensive sheets of ice to flow to so great a distance 

 from their birthplace ? Not gravitation, surely. If gravita- 



