PREFACE. V 



course. By judicious selection of material to be presented and omitted, 

 the volumes will be found useful for briefer courses, and by the use of 

 the numerous references to the fuller discussions of special treatises, 

 they may be made the basis for more extended courses than are commonly 

 given in undergraduate work. The attempt has also been made to make 

 the volumes readable, in the belief that many persons not in colleges or 

 universities will be interested in following a connected account of the 

 earth's history, and of the means by which that history is recorded 

 and read. Antecedent elementary courses in geology will not be neces- 

 sary to the use of these volumes, though such courses may be helpful. 



The arrangement of themes adopted is such as to bring to the fore 

 processes with which all students are immediately in contact, and which 

 are available for study at all seats of learning. The commoner geologic 

 agents, such as the atmosphere and running water, have been elabo- 

 rated somewhat more fully than is customary, and the common rather 

 than the exceptional phases of the work of these agents have been 

 emphasized, both because of their greater importance and their universal 

 availability. The text has been so shaped as to suggest field work in 

 connection with these topics especially, since work of this sort is every- 

 where possible. 



After the prehminary outline, which is intended to give some idea 

 of the scope of the science, and of its salient features, and to show the 

 relations of the special subjects which follow, the order of treatment is 

 such as to pass from the commoner and more readily apprehended por- 

 tions of the subject to those which are less readily accessible and more 

 obscure. Following the same general conception, the treatment of the 

 topics is somewhat graded, the earlier chapters being developed with 

 greater simplicity and fullness, while the later are somewhat more con- 

 densed. 



Many acknowledgments are made in the text and foot-notes, but 

 it is impossible to adequately acknowledge all the sources which have 

 been drawn upon, since the whole body of literature has been laid under 

 contribution. The authors especially acknowledge the generous assist- 

 ance of Professor J. P. Iddings in connection with the chapter on The 

 Origin and Descent of Rocks; of Dr. F. R. Moulton, Professor C. S. 

 SHchter, Professor L. M. Hoskins, Mr. A. C. Lunn, and Mr. W. H. 

 Emmons in connection with mathematical problems ; of Professor C. R. 



