X PREFACE. 



M. Wheeler, First Lieutenant of Engineers, U. S. A. : to J. Col- 

 lett, of the Indiana Geological Survey ; to J. Knapp, of Louis- 

 ville, Kentucky ; to G. C. Broadhead, State Geologist of Missouri ; 

 to J. W. Dawson, Principal of McGill University, Montreal ; to 

 E. Billings, of the Canadian Geological Survey, and one of the 

 hest workers among fossils on the continent ; to S. "W. Johnson, Pro- 

 fessor of Agricultural and Analytical Chemistry, for information on 

 chemical subjects ; to the Zoologist, A. E. Verrill, for the revision of 

 the zoological pages ; to F. V. Hayden, Geologist in charge of the 

 " Geological Survey of the Territories," for information pertaining to 

 the Geysers and the geological structure of th© Rocky Mountain re- 

 gion ; and, through Dr. Hayden, to W. H. Holmes, his artist, for 

 drawings of geological scenes in the mountains ; to James T. Gard- 

 ner, Geographer in Surveys of the Territories, for facts with regard 

 to the topographical features of the summit region and the western 

 slope of the Rocky Mountains ; and to G. W. Hawes, assistant in the 

 Sheffield Scientific School, for analyses of plants, bearing on the ques- 

 tion of the origin of coal. 



To F. H. Bradley, I am under still greater obligations. For 

 the work, besides having had the benefit of his careful and untiring 

 labor in the revision of the proofs, has profited in various jDarts by 

 his extensive knowledge of American Geology, rendered thorough and 

 critical by personal investigations in several of the States and Terri- 

 tories. 



The general arrangement of the work is, in the main, unchanged. 

 The science still seems to be best presented by bringing forward first 

 the Lithological or descriptive part ; next, the Historical, with inci- 

 dental illustrations of the methods of change and progress ; and then, 

 the Dynamical, this last part including a systematic review of causes 

 and their effects. But those who prefer it can combine the descriptive 

 and dynamical portions at their pleasure. It is best, in any case, 

 whenever the science is taught by recitations, to accompany the recita- 

 tions on the Lithological and Historical parts by lectures on the vari- 

 ous topics under the Dynamical ; and then, when the latter part of the 

 volume is reached in the course, the student will be prepared to make 

 thorough work with it. 



New Haven, Conn., March 1, 1874. 



