and contemporaneous Deposits of South America. 431 



turally led to conclude, that this was the chief agent in the enormous amount of 

 transportal formerly effected over a more extended area. It would indeed require 

 the strongest evidence to make one believe that the surface of the sea, or even of 

 rivers, between lat. 41° and 42°, had ever been frozen thickly enough to enclose the 

 huge masses of rock which we now find stranded on the island of Chiloe. The an- 

 gularity of their forms at this latter place and at Santa Cruz, accords with their 

 transportal by icebergs ; but it is not improbable that the other agency, namely, 

 the freezing of the sea, may formerly have been instrumental in Tierra del Fuego, 

 and especially in the southern parts of that country, where the boulders frequently 

 show signs of attrition, as if they had been worn on a sea-beach. In endeavouring, 

 therefore, to determine, in any country where boulders occur, the nature of the 

 climate during their dispersal, we should attend not only to the character of the 

 contemporaneous organic productions, but likewise to the shape of the fragments 

 and to their position ; for these circumstances would aid us in discovering whether 

 they had been imbedded in sheet-ice, or carried on the surface of deeply-floating 

 icebergs. 



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