Vlll PREFACE 



not go. For further and more detailed study of the fossils 

 themselves other books furnish ample material. 



The author is indebted to many persons for aid in the prepa- 

 ration of this volume, and in particular wishes to express his 

 gratitude to the following for criticism of various portions of the 

 manuscript and for the loan of illustrations : 



R. S. Bassler of the United States National Museum, Louis 

 Hussakof of the American Museum of Natural History, Gary N. 

 Calkins and Amadeus W. Grabau of Columbia University, John 

 M. Clarke and Rudolph Ruedemann of the New A^ork State 

 Geologic Survey, Charles Schuchert and Richard S. Lull of 

 Yale University, Percy E. Raymond and William F. Clapp of 

 the Museum of Comparative Zoology, Harvard University, 

 Francis N. Balch of Boston, Robert T. Jackson and Joseph 

 A. Cushman of the Boston Society of Natural History, Charles 

 H. Warren and R. P. Bigelow of the Massachusetts Institute 

 of Technology, Edward S. Morse of the Peabody Academy of 

 Science, Salem, and S. W. Williston of Chicago University. 



To G. R. Wieland of Yale University he feels especially in- 

 debted for most valuable suggestions on, and the loan of illus- 

 trations for, the chapter on plants. The original drawings in 

 the book owe much to the scientific knowledge and personal 

 interest which their delineator, Mr. J. Henry Blake of Cam- 

 bridge, has contributed to their execution. 



