338 Proceedings of the Royal Physical Society. 
of warm water, and of air charged with aqueous vapour, from 
the south-western regions of the Atlantic to the region lying 
far to the north-east. 
While the land stood at the higher level referred to, and 
the sea was excluded from the North Sea area, the climatal 
conditions on the eastern side of Britain were decidedly colder 
than at present, as a direct consequence of that elevation, 
and the exclusion of the sea. Rapid condensation of the 
vapour-laden currents of air travelling north-eastward with 
the Gulf Stream resulted in consequence. On the west of 
Britain, and of Norway, this precipitation took the form of 
rain, while on the east of Britain and of Scandinavia, the 
same precipitation was congealed into the form of snow. 
The east of Scotland, therefore, experienced a colder climate 
than was found in the west. Rain fell on the one side, snow 
on the other. Hence arose glacial conditions. Snow once 
on the surface, the temperature of the superincumbent air 
could not rise above the freezing-point. So matters, so far 
as climate is concerned, went on from bad to worse, until in 
the end—the east of Scotland first, and eventually even the 
west, became enveloped in a thick mass of ice. This flowed 
outward from the principal areas of high ground over the 
low lands adjoining, modifying the surface features to 
an extent that is not yet fully appreciated even by 
northern students of glacial geology. Great quantities of 
detritus were transferred within the ice itself (possibly some 
even on it, and some beneath), and these eventually, when 
the movement of the ice ceased and it began to melt away, 
were left beneath the ice as a kind of sediment, which now 
forms the Till; while the material liberated near the surface 
was washed down the gradually-widening crevasses, and 
eventually left as Eskers or Kaims.1 
When rain falls on the surface, most of it flows off under 
the influence of gravitation, and the load upon any given 
part of the earth’s crust is not perceptibly increased. When 
snow forms and gives rise to glaciers, the load on the surface 
1 This explanation, which is now well known under the title of the 
englacial theory of the origin of glacial deposits, was first put forward by 
the present writer in a paper ‘‘On Drift,” Geological Magazine, November 1874. 
