A Period in the History of our Planet. 25 



ration of thp surface, and becomes explicable only when we 

 consider that it was ice-banks that determined the direction of 

 these subglacierian rivers, and formed the limits of their beds.* 



Thus began the retreat. The centres towards which its 

 course was directed were, on the one hand, the far north ; on 

 the other hand, the lofty mountain-ranges of central Europe, 

 which still lie partially buried in eternal snow ; and from these 

 regions, from the mountains of Norway and of Sweden, and 

 the chains of the Alps of our continent, descend the rude wit- 

 nesses of the extension of the ice covering, those huge blocks 

 which lie scattered in the plains of Northern Germany and 

 llussia, of Switzerland, and even on the ridges of lower moun- 

 tains, as the Jura, and whose origin cannot be doubted, so char 

 racteristic is, for the most part, the species of rock which enters 

 into their composition. Torn from the ridges of the Scandi- 

 navian chain, these erratic blocks were moved forward on the 

 surface of the ice-coverings over the Baltic Sea, whose basin 

 was filled with ice instead of salt water, and deposited on the 

 plains of northern Germany on the skirts of the ice-field. From 

 the summits of the Alps in like manner, radiating in all direc- 

 tions, moved the fragments which the destroying influences of 

 the atmosphere, perhaps also the elevation of a part of the 

 chain, had broken loose from their bed, and hurled upon the 

 surface of the ice. The plains of Switzerland and the southern 

 declivities, nay, even the inland valleys of the Jura, the vales 

 of Lombardy, and the regions of eastern France, received from 

 the Swiss Alps those blocks which progressing culture has al- 

 ready applied in such quantities to industrial purposes, but of 

 which the quantity is still so great, that centuries will not suf- 

 fice to blot them from the empire of the existing. 



When the retreat of the ice-crust towards the north and 



* I cherish the conviction that the various traditions of ancient nations about 

 immense floods and inundations are referable to those times in the infancy of the 

 human race, when men inhabited only the moderate climates of the tropics, whilst 

 the northern latitudes were still covered with the glaciers of the glacial period. 

 According to this view, these traditionary floods were events similar to the in- 

 undations which even now are so often occasioned by the glitciere ; only with this 

 difference, that in proportion to the greater extension of those glaciei-s, they were 

 upon a much larger scale. 



