The Glacial Theory, 



145 



shaped current ; whereas a solid limit, during a certain time, of a 

 covering of ice as extensive as that of the South Pole, obviates all 

 the difficulties presented by such a phenomenon, such as the conti- 

 nuity and the regularity of the outlines, the uniform furrov^^s of the 

 polished surfaces of the North, the passage across the Baltic and the 

 North Sea of the blocks which lie on the surface of Germany and 

 of England, &c. In a second zone of blocks, more to the north than 

 the first, and observed likewise in Russia, to the south of the White 

 Sea, and of the lakes of Onega and Ladoga, we have a direct proof 

 of the successive and slow retreat of this covering of ice, a second 

 isopagetic line more remote than the first. If this covering of ice 

 really existed, it must at last have retired beyond the northern limits 

 of the British Islands, after having enveloped them partially or en- 

 tirely ; but so long as the northern ice had not retired to its present 

 limit, the climate of Europe must have been colder than it now is, 

 and, even when the primitive ice had abandoned the plains, groups 

 of glaciers must have remained in all mountainous countries. Hence 

 it appears natural that during the retreat of this covering of ice, 

 there must have been a period when the mountains of Scotland were 

 the focus of numerous glaciers, which at first descended from their 

 summits into the plains, but afterwards occupied only the interior 

 valleys, before disappearing completely. 



There would thus be two very distinct periods to be particularized 

 in the epoch of the existence of ice in the north of Europe, — that 

 during which the general covering enveloped the region, and that 

 when glaciers existed only in the high valleys. The dispersion of 

 erratic blocks over great spaces, across considerable depressions of 

 surface, the formation of the till, the furrowing and uniform striation 

 of the polished rocks of Sweden and of Finland, seem to me the 

 chief phenomena which have been produced by the northern covering 

 of the epoch of ice. The differences which exist as to the erratic 

 phenomenon between the north and the centre of Europe, appear to 

 me to be susceptible of easy explanation by the differences of latitude 

 and of the configuration of the surface. In Britain, the ice, at the 

 time of its greatest extension, seems to have covered completely 

 great tracts of country, and consequently rendered the fall of blocks 



on its surface, if not impossible, at least extremely rare ; so that the 



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