560 PREHISTORIC EUROPE. 



The closing phase of that Age was one of extreme glacial 

 conditions ; when it passed away, the Postglacial Period began. 

 And I think it is a strong confirmation of the correctness of Dr. 

 Croll's views that the last cold epoch of the Ice Age was suc- 

 ceeded by the genial climate which characterised Europe in 

 early Postglacial times. It might have told somewhat against 

 the validity of his theory had the great cycle of Glacial and 

 Interglacial conditions come to a close with a period of such 

 intense glaciation as that which distinguished the deposition of 

 the later moraines, upper boulder-clay, and valley-loss. But it 

 is quite in keeping with that theory that alternations of less 

 strongly -marked genial and cold conditions should recur in 

 Postglacial times, when the eccentricity of the earth's orbit, 

 although diminishing, was still considerably in excess of what it 

 is at present. Accordingly, we find that the genial period of 

 early Postglacial times was succeeded by a relapse to colder 

 conditions, when local glaciers again made their appearance in 

 many mountain -valleys of Scotland. The extreme freshness 

 of the glacial phenomena in those regions, which has often been 

 referred to as telling against the antiquity of the Glacial Period, 

 is thus due to the fact that they belong to Postglacial times. 

 Whether the later changes of climate and minor oscillations of 

 the sea-level in North- western Europe are the final effects pro- 

 duced by diminishing eccentricity, or whether, as Dr. Croll has 

 suggested, they may have some connection with changes in the 

 obliquity of the ecliptic, I must leave to be discussed at some 

 future time. I will only say that the phenomena referred to 

 can hardly have been produced by mere elevations and depres- 

 sions of the land, but are much more likely to owe their origin 

 to cosmical causes. Should this eventually prove to be the 

 case, we shall thereby acquire a more exact date for the later 

 Prehistoric Ages than we are ever likely to obtain by any of 

 the various ingenious methods of computation which have been 

 devised by geologists. 



Thus, although I have drawn a line of demarcation between 

 the Pleistocene and the Postglacial periods, they must yet be 



