part 1] 



ARCTIC FLOEA OF THE CAM YALLEY. 



15 



A definite cause must have underlain such differences, and tiiere- 

 fore the question arises : ' To what can they be attributed ? ' 



Supposing that the two tloras were separated by a considerable 

 interval of time, that alone would probably have accounted for 

 their dissimilarity, and this would have been the case had they 

 lived during different cold periods. On this hypothesis, the Barn- 

 well plants might have co-existed approximately with the Arctic 



Fig. 2. — Curve representing the relative 'positions of the Cam and 

 Lea-Valley Floras, based on the theory that the former lived 

 nearer the climax of a cold period than the latter. 



B__BARNWELL or 

 CAM VALLEY FLORA. 



M LEA VALLEY 

 FLORA 



TIME 



flora of Hoxne ; but the botanical evidence alone is insufficient to 

 justify such a conclusion, more especially as a considerable number 

 of years have elapsed since the Hoxne Flora was investigated, while 

 the stratigraphical evidence which places the Barnwell gravels 

 fairly late in the Pleistocene renders this interpretation improbable. 

 If, on the other hand, the two Arctic floras lived within the 

 same cold period, their differences might be partly explained by 

 supposing that the Cam-Valley Flora existed whan the cold was 

 near its climax, while the Lea- Valley Flora lived when it was less 



