IV THE ICE AGE AND ITS WORK 81 



Ice Age, glaciers radiated ; but many facts prove that 

 during its maximum development these separate glacier 

 systems became confluent, and formed extensive ice- 

 sheets which overflowed into the Atlantic Ocean on 

 the west, and spread far over the English lowlands on 

 the east and south. This is indicated partly by the 

 great height at which glacial striae are found, reaching 

 to 2,500 feet in the Lake District and in Ireland, 

 somewhat higher in North Wales, and in Scotland to 

 nearly 3,500 feet ; but also by the extraordinary distri- 

 bution of erratic blocks, many of which can be traced 

 to localities whence they could only have been brought 

 across the sea. The direction of the glacial striae and 

 of the smoothed side of ice-worn rocks also indicate 

 that the shallow seas were all filled up by ice. The 

 Outer Hebrides, for example, are all ice-ground from 

 the south-east and east, showing that the deep channel 

 of the Minch was filled up, and that the Scotch ice- 

 sheet flowed completely over the islands. On all sides 

 of Ireland, except the southern coast, the ice flowed 

 outward, but on the north-east the flow was diverted 

 southward, and on the extreme north, westward, by the 

 pressure of the overflowing ice-sheet of Scotland which 

 here encountered it. In like manner, the ice-marks on 

 the east coast of Ireland and the west coast of Wales are 

 diverted southward by the mutual pressure of their ice- 

 sheets, which, together with that of the west of Scotland, 

 filled up St. George's Channel. That such was the case 

 is further proved by the fact that the Isle of Man is ice- 

 ground in a general direction from north to south, and to 

 the summit of its loftiest mountains which rise to a height 

 of over 2,000 feet. This could only have been done by an 

 ice-sheet flowing over it, and this view is further supported 

 by some most remarkable facts in the dispersal of its local 

 erratics. These are always found to the south of the 

 places where they occur in situ, never to the north ; and, 

 what is still more noteworthy, they are often found far 

 above the native rock. Thus, boulders of the peculiar 

 Foxdale granite are found about 1,400 feet higher than 



VOL. I. • G 



