METHODS — PAL^ONTOLOGICAL 49 



processes of evolution and the course of geographical arrange- 

 ment. The bones and teeth afford admirable means of tracing 

 the gradual steps of modification by which the modern 

 mammals have arisen from very different ancestors and of 

 following their wanderings from region to region and continent 

 to continent. It is to these questions that most of the subse- 

 quent chapters are devoted. 



