78 GEOLOGY OF THE ISLE OF WIGHT 



this wonderful chapter of the world's history. But we 

 must know a little of how the story has been made out. 

 We have already seen that the changes in plant and 

 animal life point to a change from a hot climate, through 

 a temperate, at last to arctic cold. Again, over the 

 greater part of Northern England the rocks of the various 

 geological periods are buried under sheets of tough clay, 

 called boulder clay, for it is studded with boulders large 

 and small, like raisins in a plum pudding. No flowing 

 water forms such a deposit, but it is found to be just like 

 the mass of clay with stones under the great glaciers and 

 ice sheets of arctic regions ; and just such a boulder clay 

 may be seen extending from the lower end of glaciers in 

 Spitzbergen, when the glacier has temporarily retreated 

 in a succession of warm summers. The stones in our 

 boulder clay are polished and scratched in a way glaciers 

 are known to polish and scratch the stones they carry 

 along, and rub against the rocks and other stones. The 

 rock over which the glacier moves is similarly scratched 

 and polished, and just such scratching and polishing is 

 found on the rocks in Wales and the Lake District. 

 Again, we find rocks carried over hill and dale and right 

 across valleys, it may be half across England. We can 

 trace for great distances the lines of fragments of some 

 peculiar rock, as the granite of Shap in Westmorland ; and 

 even rocks from Norway have been carried across the North 

 Sea, and left in East Anglia. This will j ust give an idea how 

 we know of this strange chapter in the history of our land. 

 For, by this time it was our land England much as we 

 know it to-day ; though at times the whole stood higher 

 above sea level, so that the beds of the Channel and the 

 North Sea were dry land. But, apart from variation of 

 level, the geography was in the main as now. 



The ice sheet did not come further south than the 

 Thames valley. What was the country like south of 

 this ? Well, you must think of the land just outside the 



