1. 



described. Theories of diastrophism thai have been proposed for certain 



structural systems are summarized, and current concept! of mmintalii 

 building and continental development .ire presented where ap propr j 



INTRODUCTION 



PURPOSE OF BOOK 



The purpose of the book is to describe the structural evolution of the 

 North American continent. The chapters concern the formation and con- 

 stitution of the mountain systems, basins, arches, and volcanic archi- 

 pelagos; the beveling of the highlands; and the filling of the basins. In 

 short, they treat of the procession of deformational and sedimentary 

 events. Not only does the book seek to chronicle the crustal unrest of 

 the continent, but it also tries to summarize the supporting evidence. 



The igneous provinces and their relation to the tectonic provinces are 

 treated. The advances in geophysics in deciphering deep crustal structure 

 are referred to, and the constitution of the crust in several regions is 



METHOD OF PRESENTATION 



The structural history of the continent is one both of time and of geo- 

 graphic position. The major scheme of organization of the book could, 

 therefore, follow one or the other. For instance, if organized on a time 

 basis, all the structural events over the whole continent would be re- 

 viewed period by period. If on a geographic basis, the structural history 

 of each major province would be followed from the beginnil .'en- 



zoic time to the present. Neither course when rigidly pursued worked out 

 well, but if the chapter headings are scanned, it will he apparent that l 

 phasis in organization has been placed on geographic position. 



The necessity of treating a succession of deformational events in a cer- 

 tain province without serious interruption early became plain, and it 

 decided that the great mountain systems whose histories run through 

 several periods of time must be treated as units. The growth of the con- 

 tinent in its several provinces has been described first during the Paleo- 

 zoic, and then, in general, the great structural units of the MesozotC and 

 Cenozoic have been considered. In the resume of the structural evolution 

 of the continent, Chapter 3, the paleogeologic and paleotectonic maps are 

 presented, and there the development, period by period, is reviewed. 



KINDS OF ILLUSTRATIONS 



Considerable effort has been made to illustrate every important point 

 developed in the text. Maps, cross sections, and block diagrams are used. 

 Photographs have little value because the structural features described 

 are usually immensely larger than photographs reveal. If the reader de- 

 sires to know the nature of the topographv, other books with a wealth of 

 photographs should be referred to, such as Fenneman's Physiography of 

 the United States, Lobeck's Gcomorplwlogy. Hinds's Geomorphology, and 

 Atwood's Physiography of North America. 



