Preface ix 



ACKNOWLEDGMENTS 



A book of this kind is in effect a distillation of information in the 

 literature and the ideas from one's own research program extending 

 over many years. It is therefore with deep thanks that I acknowledge 

 my indebtedness to all those who have published on this subject 

 and to the John Simon Guggenheim Memorial Foundation, the Re- 

 search Board of the Graduate College of the University of Illinois, 

 and especially to the Illinois Natural History Survey for generous 

 support of research activities. I am grateful also to a host of scientific 

 colleagues in many institutions and countries who have been of 

 assistance in many ways and to all my students for vigorous stimu- 

 lation. 



During the preparation of the manuscript I have been greatly in- 

 debted to the following persons for valuable discussion, suggestions, 

 and criticisms: Sidney W. Fox, Florida State University; Harlan 

 Lewis, University of California at Los Angeles; Everett C. Olson, 

 University of Chicago; H. B. Willman and David Swann, Illinois 

 Geological Survey; J. B. Kitzmiller, J. R. Laughnan, and W. M. Luce, 

 University of Illinois; and M. W. Anderson, P. W. Smith, and L. J. 

 Starinard, Illinois Natural History Survey. 



I am especially indebted to Harlow B. Mills, Illinois Natural His- 

 tory Survey, and to Alfred E. Emerson, University of Chicago, for 

 counsel and encouragement during the preparation of this book. 



For scientific editorial assistance, I am extremely grateful to my 

 wife Jean and also to my son Charles A. Ross and his wife June 

 Phillips Ross. 



I am grateful also to many publishers and authors for permission 

 to reproduce a number of illustrations and to others who kindly 

 loaned illustrations for use in this book. Specific acknowledgment 

 is made under each such illustration. Finally I wish to thank the 

 staff of Prentice-Hall, Inc., for the preparation of many original 

 figures and for editing the manuscript. 



Herbert H. Ross, Illinois Natural 

 History Survey. Urbana, Illinois 



