CHAP. XIII.] PLEISTOCENE EPOCH. 277 



examine the work it has done and the deposits it has left 

 behind, but a country from which an ice-sheet has recently 

 retreated has yet to be found and described. It is quite 

 conceivable that the action of an extensive ice-sheet may be 

 different from that of a single glacier ; while the action of 

 sea-ice on a sinking shore is likely to be very different from 

 both. 



As however very little is known about these agencies, 

 the students of Glacial deposits labour under the disad- 

 vantage of being without positive knowledge of what takes 

 place at the present day under the conditions which they 

 postulate as having existed at a past period in Britain. 

 They are obliged to draw largely on the imagination, and 

 there has been a great tendency to refer all the phenomena 

 of the Glacial epoch to one set of conditions or the other 

 without duly considering the differences of the deposits. 

 Probably in this, as in so many other much debated ques- 

 tions, the truth lies between the opposite extremes, and the 

 investigator who is most likely to arrive at the truth is he 

 who takes care to steer a safe course between the Scylla 

 of universal land-ice on the one hand, and the Charybdis 

 of floating icebergs on the other. 



In the following pages I shall not attempt to give a 

 complete history of the physical and geographical changes 

 which took place in the British area, but shall content 

 myself with giving some reasons for not accepting the 

 accounts which have been given by Professor James Geikie, 1 

 and shall then fix the reader's attention on certain epochs 

 concerning which there is a more general agreement of 

 opinion. 



In the first place, Professor James Geikie probably errs 

 in attributing all ice-scratched surfaces to the action of 

 land-ice, and in not admitting that some of them may be 



1 In " The Great Ice Age " and " Prehistoric Europe." 



