158 DISCUSSION OF THE DESICCATION QUESTION. 



the desiccation of the region of the Cordilleras, has been found out within a 

 very recent period, nothing at all having been known of either change of 

 conditions previous to the commencement of the California Survey in 1860. 

 But the fact of the former glaciation of portions of the country east of the 

 Mississippi and about the Great Lakes had been femiliarly known, and much 

 commented on, twenty or more years before that time. And the same thing 

 is true of certain parts of Europe : glaciers — both as at present existing 

 and as occupying a much larger area in former times — have occupied a 

 large share of the attention of geologists during almost half a century. 



To the reader, then, it might have seemed natural that the phenomena 

 of extinct glaciation in Northeastern North America and in Europe, as well 

 as in other parts of the world, should have been described in connection with 

 that which has been said on the same subject in a preceding chapter, in ref- 

 erence to the region of the Cordilleras. This, however, was not necessary, 

 or even possible. For, in the first place, the body of facts collected by vari- 

 ous observers is too large to be brought within such moderate space as the 

 present volume affords ; and, in the second place, the jaosition of the present 

 Avriter with regard to the phenomena of extinct glaciation in the Cordilleras 

 was a peculiar one, rendering it justifiable in him to endeavor to collect 

 together, for the first time, the principal facts, so that a clear idea might 

 be had of their scope and bearing; while at the same time attention was 

 called to some of the remarkable errors into which observers inexperienced 

 in this department of geological investigation had fallen : this it was neces- 

 sary to do, since leaving these mistakes uncorrected would have much 

 increased the difficulty of the subsequent discussion. To a rapid review 

 of the principal fiicts connected with both extinct and present glaciation 

 our attention will be naturally directed in the last chapter of the present 

 work, when, having set forth the principal focts connected with the desicca- 

 tion of a large portion of the earth, and endeavored to account for the 

 same, it will have become necessary to show that the former greater exten- 

 sion of the glaciers over certain regions is not necessarily a condition of 

 things in conflict with what appears to the writer to have been the course 

 of events during the geological ages preceding and following the so-called 

 glacial epoch. 



That, on the other hand, the phenomena of desiccation should have been 

 taken up as manifested in other regions than in the Cordilleras, as has been 

 done in the preceding chapter, is to be explained by reference to the facts 



