PREFACE. 



In the preparation of the new edition of this Manual, the work has 

 been wholly rewritten. North American Geological History is still, how- 

 ever, its chief subject. The time divisions in this history, based on the 

 ascertained subdivisions of the formations, were first brought out in my 

 Address before the meeting of the American Association at Providence in 

 1855 ; and in 1863, the " continuous history " appeared in the first edition 

 of this Manual, written up from the State reports and other geological pub- 

 lications. The idea, long before recognized, that all observations on the 

 rocks, however local, bore directly on the stages in the growth of the Con- 

 tinent derives universal importance from the recognition of North America 

 as the world's type-continent — the only continent that gives, in a full and 

 simple way, the fundamental principles of continental development. 



Since 1863, when the first edition of this work was published, investi- 

 gation, through the geological workers of the United States, Canada, and 

 Mexico, has been extended over nearly all parts of the continent, so that its 

 history admits of being written out with much fullness. The Government 

 Expeditions over the Rocky Mountain region, under F. V. Hayden, Clar- 

 ence King, Captain Wheeler and others, and earlier, those especially of 

 the Pacific Railroad Explorations, and the Mexican Boundary Commission, 

 were large contributors to this result ; and also, since 1879, the able corps of 

 the United States Geological Survey. 



As the rewritten book shows, new principles, new theories, and widely 

 diverse opinions on various subjects are among the later contributions, along 

 with a profusion of new facts relating to all departments of the science. 



The Cambrian formation has been traced through a large part of the 

 continent, and the number of its fossils has been increased, chiefly by C. D. 

 Walcott, from a few to hundreds. The Appalachian Mountain structure 

 has been shown by Clarence King, Dr. G. M. Dawson, and R. G. McCon- 

 NELL to have been repeated in the great post-Cretaceous mountain-making 

 of the Rocky Mountain region. The Reptiles, Birds, and Mammals of the 

 Mesozoic and Tertiary have continued coming from the rocks until the 

 species recognized much outnumber those of any other continent. The canons 

 and other results of erosion in the west have thrown new light, through 

 their investigators, on the work of the waters. Besides, the science of 



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