PREFACE 1X 
In the preparation of this book, I am indebted to my 
colleagues at Cornell, Professors Harris and Gill, for sug- 
gestions and other aid. I have also drawn upon all the 
available literature, and have endeavored to do so carefully. 
Mistakes and misinterpretations may have crept in, but I 
believe that the book is as free from them as could well be 
expected. For illustrations I have depended largely upon 
the materials in the geological laboratory of Cornell Uni- 
versity, and the majority of these are original. Other 
illustrations are obtained from various sources, for which 
acknowledgment is made in the list on the succeeding pages. 
To those who have kindly allowed me the use of photographs 
not before published, I return especial thanks. These and 
the other borrowed illustrations will add greatly to the value 
— of the book. 
RALPH S. TARR. 
IrHaca, N. Y., Nov. 16, 1896. 
