16 MISS M. E. J. CHL^XDLER OX THE ^vol. Ixxvil, 



marked : wherefore, of the two floras, that from the Cam Yallev 

 would natm*ally show the more pronounced Arctic features. Hence, 

 if the two were supjjosed to lie on a curve, so drawn that ordinates 

 represent intensity of cold and abscissae represent time, the 

 Cam- Valley Flora would lie at a higher point on the curve than 

 the Lea -Valley Flora. 



Thns A or B (fig. 2, p. 15 i would represent diagrammatically 

 the relative position of the Cam- Valley Flora if the Lea -Valley 

 Flora were supposed to lie at L or M on the cmwe. If L were its 

 position, the Cam- Valley Flora Avould be the younger of the two, 

 whether it were represented by A or B, and similarly if M Avere 

 its position, then the Cam- Valley Flora would be the older. 



Another possible explanation of the more striking character of 

 the Arctic element at Barnwell is based on the theory, previously 

 suggested, that the most Arctic plants grew on the high ground 

 upstream. But the high ground, which both in the Lea and in 

 the Cam Valleys was formed by Chalk, was near to Barnwell, in 

 the Cam Valley, while it lay much farther away fi'om Ponders End 

 in the Lea Valley; thus seeds from the upland tract had a good 

 chance of incorporation in the peat-seams at Barnwell. Avhereas in 

 the Lea Valley they Avere more liable to be destroyed during 

 transport. 



The relative distance between the peat-beds and the Chalk 

 uplands in the two localities would also explain why the calcareous 

 element as Avell was better represented at Barnwell than at Ponders 

 End. 



Perhaps, if the suggestion that the floras lived during the same 

 cold period be correct, both the causes indicated here may have 

 helped to produce a cei-tain individuality in the plant-beds of the 

 two areas. 



Though it is possible, then, to regard the floras as contemporary, 

 the evidence yielded hitherto by the plants is insufficient to justify 

 any definite conclusion, and, at present, it looks as if the testimony 

 afforded by other lines of research must be awaited for the final 

 solution of the problem. 



I desire to take this opportunity' of thanking I\Irs. Eeid for 

 generously alloAA^ng me to use the magnificent Eeid Collection, and 

 for the assistance which she willingly gave me while I was at work 

 on these beds. My thanks are also due to Prof. J. E. Marr, F.P.S., 

 who kindly gave me every facility for Avorking in the SedgAvick 

 Museum. I am further deeply grateful to Miss Gr. L. Elies, D.Sc, 

 for reading and criticizing this paper in manuscript, and for all 

 the unoTudging help and encouragement Avhich she has always 

 iifforded me. 



