A Period in the History of our Planet. 27 



The same relations must also have come into existence when 

 the ice-crust was exposed to the destructive influences which a 

 condition of heat like ours at the present day must have brought 

 along with it. In the plains began, as we have already re- 

 marked, the contest, in which death itself was to succumb, and 

 the new life of our present creation to conquer. Attacked 

 from without by the beams of the sun, and from within by the 

 rays of the earth's own warmth, the ice dwindled away, and 

 the more land became free so much the more powerful became 

 the forces which supported the contest. But just where the 

 ice disappeared, on the boundaries of the ice-field, was the 

 seat of the more active movement, which, finding its point of 

 support in the before-mentioned centres, proceeded from thence 

 in every direction ; for the most considerable movement of 

 the ice-masses is always at those places where heat can exert 

 the greatest influence upon them. But if the destructive in- 

 fluences preponderated at the limits, the forming elements did 

 so at the centres, and the masses collected there consequently 

 pressed downwards to the contest as a fresh reserve, carrying 

 along with them fragments of their formation-sites — the erratic 

 blocks. From the distribution of the various alpine rocks 

 upon the chains of the Jura, as well as from the extension of 

 the zones of blocks that descend from the heights of Scandi- 

 navia, it will some time or other be possible to calculate the 

 time which was required for the retreat of the ice-covering 

 into its narrower limits. 



But vain was the contest. More and more was the ice-mass 

 compelled to recoil, more and more was the land denuded, to 

 become covered with verdure. The plains of Germany, Rus- 

 sia, France, and Italy, were rescued from their frozen state ; 

 the Baltic was set free ; the north sea, for the most part, was 

 anew covered with waves. But the more considerable chains 

 of mountains, presenting, by their elevation above the sea- 

 level, a more secure resting-place to the ice-covering, still re- 

 tained the eternal winter upon their summits and in their val- 

 leys, and thus there arose detached glacier ranges, which no 

 longer formed a connected whole, like their common ances- 

 tress, but separate groups, each of which belonged to a par- 

 ticular mountain range. The Scandinavian peninsula, the 



