132 DISCUSSIONS IN CLIMATOLOGY, 



having lived at 54° N. lat. in England, quite close to 

 the time of the Glacial Epoch, is absolutely inconsistent 

 with a mere gradual amelioration of climate from that 

 time till the present day. The immense quantity of 

 vegetable food which this creature requires, implies a 

 mild and uniform climate with hardly any severe 

 winter; and no theory that has yet been suggested 

 renders this possible, except that of alternate cold and 

 warm periods during the Glacial Epoch itself. . . . 

 Thus the very existence of the hippopotamus in 

 Yorkshire, as well as in the south of England, in close 

 association with glacial conditions, must be held to be 

 a strong corroborative argument in favour of the 

 reality of an interglacial warm period." 



I trust that Mr. Wallace has not been misled by 

 Mr. Wood's unfortunate use of the term "Postglacial " 

 as applied to the Hessle boulder -clay. The Hessle 

 boulder-clay as surely belongs to the Glacial Period 

 proper as does the true Till of Scotland, which covers 

 the Lowlands and overlies the interglacial beds of 

 that country. It is the moraine profonde of the last 

 mer de glace, which covered the greater part of North- 

 western Europe. The Upper Till of Scotland and the 

 Hessle boulder-clay of England belong to the same 

 period. This has been clearly shown by Professor J. 

 Geikie in his " Great Ice- Age," chap. xxx. (2nd edit.), 

 and in " Prehistoric Europe," chap, xii., and elsewhere. 

 The Hessle boulder-clay is, in short, a continuation of 

 the Upper Till of Scotland. 



The position of these Hessle beds to which Mr. 

 Wallace refers, like that of the interglacial bed. f 

 Scotland, is between two boulder-clays — the Hessle 

 and the Purple boulder-clays, both of which indicate 

 a period of extreme glaciation: only the Purple 

 boulder-clay period was somewhat the more severe 



