iv PREFACE 



Students beginning the study of geology usually have either 

 very little knowledge of biology or their study has not emphasized 

 the classification of organisms. The evolution of organisms is a 

 fundamental consideration in the study of earth history, and the 

 instructor finds it well-nigh necessary to present to his classes out- 

 line classifications of plants and animals accompanied by brief 

 descriptions of the more common types. Such matter is presented 

 in the first chapter of this book. 



In certain texts, especially those portions dealing with historical 

 geology, there is a tendency to overwhelm the student by the intro- 

 duction of a multiplicity of technical terms, especially the names of 

 fossils. The present author's idea has been to reduce such terms 

 to a reasonable minimum required for a proper understanding 

 of the great principles of earth history. The genus and species 

 names accompanying illustrations are given in the interest of 

 scientific accuracy and with no thought that these are to be re- 

 membered by the student. 



Various distinctly appropriate illustrations, more or less familiar 

 because of their appearance in other text-books or manuals of 

 geology, have not been abandoned merely for the sake of some- 

 thing new or different. Many of the illustrations, however, ap- 

 pear in a text-book here for the first time. Among the numerous 

 original sources of illustrations, particular mention should be made 

 of the publications of the United States Geological Survey, the 

 New York State Museum, The American Museum of Natural 

 History, and the Maryland Geological Survey. 



The Macmillan Company, Henry Holt and Company, 

 Ginn and Company, D. Appleton and Company, and John 

 Wiley and Sons have generously allowed the use of various 

 cuts. Careful attention has been given to the selection of 

 only such views, fossils, diagrams, and maps as would system- 

 atically illustrate the text without overdoing this feature of 

 the book. 



The author is under particular obligation to Professor Bailey 

 Willis of Stanford University for the use of his excellent series of 

 paleogeographic maps of North America. These maps, together 

 with his U. S. G. S. Professional Paper 71, have proved to be 

 veritable storehouses from which to draw in the preparation of the 

 manuscript of this book. 



The well-known manuals and text-books of geology, especially 



