ICE PERIOD. 297 



the breaking up of this universal shroud the 

 ice must have Hngered longest in mountainous 

 strongholds, and that all these fastnesses of 

 retreat became, as the Alps are now, centres 

 of distribution for the broken debris and 

 rocky fragments which are found scattered 

 with a kind of regularity along certain lines, 

 and over given areas in northern and central 

 Europe. How he followed out this idea in 

 his subsequent investigations will be seen here- 

 after. 



