vi PREFACE. 



account the agency both of land ice and sea-borne ice in 

 many forms, along with repeated and complex elevations 

 and depressions of large portions of the continent, in 

 order to account for the effects observed. He is disposed, 

 however, to seek for the causes of changes of climate 

 rather in geological and geographical agencies than in 

 astronomical vicissitudes, some of which are too slow and 

 uncertain in their operation, and others altogether con- 

 jectural. Such views are less sensational than those which 

 invoke vast and portentous exaggerations of individual 

 phenomena, but they are likely, in the end, to commend 

 themselves to serious thinkers, especially when they are 

 confirmed by the facts observed in the regions which are, 

 of all others, best suited for the study both of extinct and 

 recent ice-action. 



The basis of the work rests on the observations of the 

 author, but reference will be made to the large and im- 

 portant contributions of JDr._ G. M. Dawspn, Dr. Bell, 

 Dr. Ells, Mr. Whiteaves, Mr. Chalmers, Mr. Low, Dr. 

 Spencer, Mr. McConnell, Mr. Richardson, Prof. Yule Hind, 

 Lieut. -Col. Grant, Dr. G. J. Hinde, and others, whose names 

 will be found in the subsequent pages as workers in the 

 Pleistocene geology of Canada. 



J. WM. DAWSON. 



McGiLL COLLEGE, 



MONTREAL, 1893. 



