PREFACE 



In preparing this Manual for a third edition, the section on Kinas 

 of Rocks has been changed throughout ; the Dynamical part has been 

 mostly rewritten, and has become enlarged one half, besides receiving 

 brief bibliographic lists illustrating the history of its more important 

 doctrines, and many additions to its figures ; and the Historical Geol- 

 ogy, while only partially revised, has been greatly modified with 

 reference to Green Mountain Geology, American fossil Vertebrates, 

 and the Glacial and Champlain periods of the Quaternary. In addi- 

 tion, the work is now supplemented, through the gift of Professor 

 Marsh, by twelve plates of figures illustrating species of Reptiles, 

 Birds, and Mammals, from the Jurassic, Cretaceous, and Tertiary for- 

 mations west of the Mississippi. 



The general plan of the Manual remains unchanged. Those pre- 

 ferring the more common method of arrangement can readily make 

 the instruction in Dynamics to follow directly the descriptive chapter 

 on the Condition, Structure, and Arrangement of Stratified and Un- 

 stratified rocks, under Lithological Geology. 



James D. Dana. 



New Haven, Conn., November 1, 1879. 



FROM THE PREFACE TO THE SECOND EDITION. 



Two reasons have led the author to give this Manual its American 

 character : first, a desire to adapt it to the wants of American stu- 

 dents ; and, secondly, a belief that American Geological History, on 

 account of the peculiar simplicity and unity of the system of progress, 

 affords the best basis for a text-book of the science. North America 

 stands alone in the ocean, a simple isolated individual continent, 

 even South America lying to the eastward of its meridians ; and, con- 

 sequently, the laws and agencies of progress have been undisturbed 

 by conflicting conditions and movements in other lands. The author 

 has, therefore, written out North American Geology by itself, and 



