450 LOUIS AGASSIZ. 



forms and dimensions. At East Boston you 

 cannot see what underlies this deposit ; but 

 no doubt it rests upon a rounded mass of 

 granite, polished and grooved like several 

 others in Boston harbor. . . . 



In our journey to Niagara, Mr. Desor and I 

 assured ourselves that the river deposits, in 

 which, among other things, the mastodon is 

 found with the fresh - water shells of Goat 

 Island, are posterior to the drift. It is a fact 

 worth consideration that the mastodons found 

 in Europe are buried in true tertiary forma- 

 tions, while the great mastodon of the United 

 States is certainly posterior to the drift. . . . 

 In another letter I will tell you something of 

 my observations upon the geographical distri- 

 bution of marine animals at different depths 

 and on different bottoms, and also upon the 

 relations between this distribution and that 

 of the fossils in the tertiary deposits. 1 . . . 

 Although so deeply interested by the geo- 

 logical features of the country, Agassiz was 

 nevertheless drawn even more strongly to the 



1 I have left out a portion of this letter which appeared in 

 the first edition of the book, because I learned that the facts 

 there given concerning the deposit of Zostera marina were 

 not substantiated, and that Agassiz consequently did not for- 

 ward the letter in its first form. The remainder of this 

 chapter appears in this edition for the first time. E. C. A 



