344 CLIMATIC COXDITIOXS OF THE GLAC[AL EPOCH. 



written on this class of subjects hus come from tlie pens of tliose who never 

 had an opportunity of studying regions of jjresent glaciation, and of thus 

 making themselves practically acquainted with what ice is now doing as an 

 agent of geological change. There are those who see the work of glaciers 

 everywhere, in both hemispheres, and at all epochs. Having once adopted 

 a theory of successive changes of climate which renders it easy, if not neces- 

 sary, to believe that there have been many " Glacial epochs " during the 

 geological ages, and having also convinced themselves that erosion has all 

 been the work of ice, it becomes very easy to recognize in every rounded 

 rock surface, in every accumulation of pebbles and boulders, and in every 

 striated fragment of rock, no matter where or how found, the proof of the 

 former presence of that all-powerful agent, those who protest against ignor- 

 ing other, and, as it seems to them, more powerful agencies, being looked 

 upon as hopelessly " behind the age." 



In the preceding pages of this volume the conditions and circumstances 

 which may and often do lead to mistakes in regard to the former existence 

 of ice and snow have been pointed out with sufficient detail, and instances 

 given where — as it seems clear to the present writer — it is impossible not 

 to admit that prejudice in favor of a current theory has led to misconception 

 of the facts observed,* 



In designating the regions which have at some former time been more 

 extensively glaciated than they now are, the writer will endeavor to adhere 

 as closely as possible to facts. Where differing in opinion from those who, 

 having studied the same regions, have arrived at conclusions of another 

 character, he will not seek to conceal the circumstance ; and, although space 

 may not admit a full discussion of the evidence, he will endeavor to convince 

 the reader that there are, in such cases, difficulties which at least render 

 great caution necessary, and that there are good and sufficient reasons why 

 the former presence of ice should not be taken for granted, as has often 

 been done with hardly more than a shadow of proof. 



We may begin by making the ))road statement that there are only two 

 regions in the world where the phenomena and conditions of a former glacia- 

 tion are of so peculiar a character and on so grand a scale as to give rise to 

 serious ditficulties in accounting for the facts and to make it necessarv to 

 admit the existence of conditions of climate or topography, or both, consid- 

 erably different from those now prevailing over the same portions of the 



* .See (iiilc, [ip. 10, 11, 47-51, etc. 



