INTBODDOTION. 9 



required, and profited frequently hy their advice. Mr. Stanton and Mr. Cro.s.s liav(; 

 also been consulted upon points connected with the general plan and its execution, 

 and to them and others some of the more far-reaching considerations touched upon 

 have been referred. Mj' acknowledgments should not, however, be brought to a 

 close without an expression of thanks to Miss Frances Wieser and Miss Mary- 

 Mitchell, who have executed the drawings by which the paleontologic portion of this 

 work is illustrated. 



