THE VARIATIONS OF GLACIERS 263 



years, whereas those of the southwestern slopes of the Fairweather Range and 

 those of Prince William Sound have quite lately been as extensive as they have 

 probably been for several centuries. Mr. Gilbert makes some general sugges- 

 tions of a theory to explain such curious anomalies. He also presents clearly the 

 very striking evidence which the topography of the Alaskan coast offers in favor 

 of the power of glaciers to erode their channels. The volume concludes with a 

 theoretical discussion of the influence of the sea on the pressure which tide-water 

 glaciers exert on their beds below sea-level. 



