1 U EARLY MAN IN BRITAIN. [CHAP. v. 



minimum the spotted hyaena "and hippopotamus and 

 other southern animals roamed to their northern limit. 

 Thus every part of the middle zone has been successively 

 the frontier between the northern and southern groups, 

 and consequently their remains are mingled together in 

 the caverns and river deposits, under conditions which 

 prove them to have been contemporaries in the same 

 region. In some of the caverns, such as that of Kirk- 

 dale, the hysena preyed upon the reindeer at one time of 

 the year and the hippopotamus at another. In this 

 manner the association of northern and southern animals 

 may be explained by their migration according to the 

 seasons, and their association over so wide an area as the 

 middle zone by the secular changes of climate, by which 

 each part of the zone in turn was traversed by the ad- 

 vancing and retreating animals. 



Climatal and Geographical Changes in Britain marked 

 by Glacial Phenomena. 



Secular changes of climate in the Pleistocene age are 

 clearly marked in Britain north of a line connecting the 

 Bristol Channel with the valley of the lower Thames, and 

 passing due eastward into Germany and Eussia. by the 

 traces of glaciation, by the erratics, or blocks of stone 

 transported far away from the rocks from which they 

 were torn, and by the accumulations of clay and sand 

 known as the glacial 1 drift. They imply the following 



1 The term glacial, used in a varying sense by different writers, is 

 employed in these pages merely to express the marks of the presence 

 of ice in the shape of glaciers and icebergs in the areas where they are no 

 longer found. For purposes of geological classification over wide areas 

 an appeal to the purely local phenomena of glacier or iceberg is useless, 



