770 THE JOURNAL OF GEOLOGY. 



of Harvard, by saying : " But I have not yet seen a trace of glacial 

 action proper, if polished surfaces and scratches and furrows are 

 especially to be considered as such." 1 



BIOLOGICAL EVIDENCE. 



Thus far I have confined myself to a statement of the facts 

 that relate directly to glaciation. Aside from these a matter of 

 the utmost importance is the continuity of life from Tertiary 

 times down to the present, especially in the tropical and sub- 

 tropical parts of the earth. If glaciation had been cosmic, as 

 suggested by Agassiz — if it had taken place under the very 

 equator — then the reasoning of biologists regarding the origin 

 and distribution of the present life of the globe is about all at 

 fault. A reviewer of Hartt's Geology of Brazil long ago called 

 attention to the fact that "the grand objection to the theory of 

 the former existence of a continental glacier in tropical America, 

 is the unbroken continuity of tropical life since the close of the 

 Tertiary period." 2 Mr. Wallace, in an earlier review, had already 

 called attention to the same point, 3 while still another lays stress 

 upon the important fact that the plants found in the Amazonian 

 silts, supposed by Agassiz to be of glacial origin, are the remains 

 of tropical plants, and are not therefore comparable with the 

 Alpine plants growing beside existing glaciers in mountainous 

 regions. 4 



THE OPINIONS OF OBSERVERS. 



The following are some of the opinions of geologists regard- 

 ing the phenomena regarded by Agassiz and Hartt as glacial. 

 These authors are quoted, not simply for the purpose of bring- 

 ing the weight of authority to bear on the subject, but because 

 they have all seen much of the geology of Brazil and are 

 competent to have opinions worthy of consideration. Darwin, 

 who visited Brazil in 1832 and saw something of these 



1 Journey in Brazil, 88. 



2 American Naturalist, 1871, V., 36. 



3 Nature, 1870, II., 511. 



t The Geological Magazine, 1868, V., 458. 



