INTRODUCTORY. 3 



The scope of this discussion makes it necessary to introduce a considerable 

 body of facts relating to the glacial and surface geology of regions not in- 

 cluded within the Cordilleras. These to^iics must, of course, be treated in a 

 very general way, for space would by no means permit of entering into 

 minute details in regard to all the countries necessarily embraced within tlie 

 field of so comprehensive an inquiry. To a very considerable extent the 

 writer's own observations will be relied on as forming the basis of facts on 

 which the discussion rests ; but the endeavor will be made to give due credit 

 for all the information obtained from other sources, and the reader will be 

 directed where to find such additional material as may be accessible in the 

 works of trustworthy authors, who have contributed matter of importance in 

 the line of this inquiry. 



In order to the better understanding of that which follows, it will be 

 necessary to begin with some remarks on glaciers and ice-work in general. 

 The scope of these remarks will be understood by those who read this 

 chapter, and they will also see why what may, at first view, seem to be 

 elementary considerations have been introduced into the present volume. 

 The course here to be followed is particularly necessaiy in connection with 

 Californian geology, because nowhere have such wild and absurd statements 

 in regard to the work done by ice been published as in discussing the 

 geological features of the Sierra Nevada. But it is true, also, that among 

 geologists generall}' there has been, of late years, a decided tendency to 

 exaggerate the importance of the work done by ice, and to leave out of 

 consideration the preponderating intliience of water in connection with so- 

 called glacial phenomena. In the early stages of geological discussion the 

 action of the ocean was the all-important factor : then ice had its day ; and 

 it is only quite recently that rain and rivers have begun to be recognized as 

 being also extremely important agents in the formation, transportation, and 

 deposition of detrital materials. The study of the gravels of the Sierra Nevada 

 can hardly fail to convince the candid investigator that the work of rivers 

 in that i-egion has been of great geological importance. And it is confidently 

 believed by the writer that the following chapter will fully illustrate and 

 bear out the statement that, in the Sierra Nevada at least, ice has played 

 but an extremely subordinate part as a geological agent, although there is 

 no doubt that the great Californian range was once covered with grand 

 glaciers, but little, if at all, inferior to those which now lend such a charm, 

 both from a picturesque and geological point of view, to the Swiss Alps. 



