Geology of South America 373 



Danvin landed in South America than two sets of phenomena power- 

 fully arrested his attention. The first of these was the occurrence of 

 great masses of red mud containing bones and shells, which afibrded 

 striking evidence that the Avhole continent had shared in a series of 

 slow and gradual but often interrupted movements. The second 

 related to the great masses of crystalline rocks which, underlying 

 the muds, cover so great a part of the continent. Darwin, almost as 

 soon as he landed, was struck by the circumstance that the direction, 

 as shown by his compass, of the prominent features of these great 

 crystalline rock-masses — their cleavage, master-joints, foliation and 

 pegmatite veins — was the same as the orientation described by 

 Humboldt (whose works he had so carefully studied) on the west 

 of the same great continent. 



The first five chapters of the book on South America were devoted 

 to formations of recent date and to the evidence collected on the 

 east and west coasts of the continent in regard to those gi'and earth- 

 movements, some of which could be shown to have been accompanied 

 by earthquake-shocks. The fossil bones, which had given him the 

 first hint concerning the mutability of species, had by this time been 

 studied and described by comparative anatomists, and Darwin was 

 able to elaborate much more fully the important conclusion that the 

 existing fauna of South America has a close analogy with that of the 

 period immediately preceding our own. 



The remaining three chapters of the book dealt with the meta- 

 morphic and plutonic rocks, and in them Darwin announced his 

 important conclusions concerning the relations of cleavage and folia- 

 tion, and on the close analogy of the latter structure with the banding 

 found in rock-masses of igneous origin. With respect to the first of 

 these conclusions, he received the powerful support of Daniel Sharpe, 

 who in the years 1852 and 1854 published two papers on the 

 structure of the Scottish Highlands, supplying striking confirmation 

 of the correctness of Darwin's views. Although Darwin's and Sharpe's 

 conclusions were contested by Murchison and other geologists, they 

 are now universally accepted. In his theory concerning tlie origin 

 of foliation, Darwin had been to some extent anticipated by Scrope, 

 but he supplied many facts and illustrations leading to the gradual 

 acceptance of a doctrine which, when first enunciated, was treated 

 with neglect, if not with contempt. 



The whole of this volume on South American geology is crowded 

 with the records of patient observations and suggestions of the 

 greatest value ; but, as Darwin himself saw, it was a book for the 

 working geologist and "caviare to the general." Its author, indeed, 

 fre(iuently expressed his sense of the "dryness" of the book; he 

 even says "I long hesitated whether I would publish it or not," and 



