of Secular Changes of Climate. 371 



the earlier part of the Postglacial Period in England was pos- 

 sibly even warmer than our present climate ; and that it was 

 succeeded by a refrigeration sufficiently severe to cause ice to 

 form all round our coasts, and glaciers to accumulate in 

 the valleys of the mountain districts.' ' That these fauna 

 indicate a warm and equable condition of climate is further 

 evident from Mr. Wallace's remarks : — " The fact/' he says, 

 " of the hippopotamus having lived at 54° N. lat. in Eng- 

 land, quite close to the time of the Glacial Epoch, is abso- 

 lutely 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 hippo- 

 potamus 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 w r arm 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 

 cf 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 Prof. 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 con- 

 tinuation of the Upper Till of Scotland. 



The position of these Hessle beds to which Mr. Wallace 

 refers, like that of the interglacial beds of 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 

 of the two. At both periods the greater part of North-western 

 Europe was buried under ice. We know that during the last 

 great ice-period, which was undoubtedly the period of the 

 Hessle boulder-clay, the ice-sheet reached in North Germany 

 as far as Berlin; while during the period of the Purple boulder- 

 clay it advanced to about Saxony. 



The observations of Prof. Torrell, Dr. A. Penck, Prof. 

 Credner, Prof. Berendt, Dr. Jentzsch, A. Helland, F. Wahn- 



