36 



FOSSIL TURTLES OF NORTH AMERICA. 



THE GEOLOGICAL DISTRIBUTION OF THE TURTLES. 



In tables 1 and 2 the writer has endeavored to present in as accurate and effective 

 a manner as possible the chronological distribution of the fossil turtles of North 

 America, with the positions of the turtle-bearing beds and the level at which each 

 species has been found. Table i represents the principal divisions and subdivisions 

 of the Mesozoic age, except the Triassic, while table 2 deals in like manner with the 

 Cenozoic. No small difficulty is experienct in the preparation of such tables. The 

 limits of the larger formations and the periods which they represent have not 

 received general acceptance; and when we come to consider the smaller divisions 

 and the correlation of deposits in distant regions there are in many cases widely 

 divergent views. Again, in the collection of the fossils there has often been too 

 little care exercised in preserving records of localities and levels. An interroga- 

 tion mark ( ? ) preceding any generic name indicates that the species immediately 

 succeeding possibly does not belong to the level indicated. 



