xii PREFACE 



ford Dean, and Professor I. C. Russell have kindly supplied me 

 with illustrations from their books. Mr. Lucas of the U. S. 

 National Museum, Dr. C. Hart Merriam of the U. S. Agricultural 

 Department, Professor R. D. Salisbury, Professor Calvin of the 

 Iowa Geological Survey, Mr. Pynchon of Hartford, and the offi- 

 cers of the Pennsylvania Railroad Company have furnished many 

 valuable photographs. My colleagues, Professors Magie and Lib- 

 bey, have assisted me with the proofs, and the latter has allowed 

 the free use of his collection of unpublished photographs taken in 

 Greenland, Alaska, and the Hawaiian Islands. Another colleague, 

 Dr. A. E. Ortmann, has taken great pains in the selection of 

 figures of the American fossil invertebrates, which have been re- 

 drawn by Mr. R. Weber, University Draughtsman. My friend, 

 Dr. Baur, has been my guide through the tangled mazes of the 

 synonymy of the American fossil reptiles. To these gentlemen, 

 one and all, hearty gratitude is due for oft-repeated and unstinted 

 kindness. 



No one can be more conscious than the author of the very 

 imperfect character of his performance, but he ventures to hope, 

 nevertheless, that the book may find a place of usefulness, supple- 

 mentary to the host of excellent works on Geology already in 

 existence. 



Princeton, N. J., Jan. 15, 1897, 



