PREFATORY NOTE 



The essays in this volume were presented before Section E, of the 

 American Association for the Advancement of Science, at the meeting 

 in Baltimore in December, 1908. The original plan of the papers 

 involved the formulation of the principles of correlation, as applied 

 to the formations of different periods. This plan was conceived by 

 Bailey Willis, then vice-president of Section E, and was carried out 

 with much success. The several chapters have appeared in the 

 Journal of Geology, since their presentation at Baltimore. They 

 present in broad outlines a summary of certain phases of existing 

 knowledge of North American geology, and are now bound together 

 in the belief that students of geology in this country and abroad 

 will welcome them in this more convenient form. The paleogeo- 

 graphic maps by Mr. Willis form a valuable part of the volume. 



June, 19 10 



