part 1] ARCTIC FLORA OF THE CAM YALLEY. 5 



parallel seams, were poor in leaves and twigs, but very rich in 

 small seeds and in tiny black galls. 



To what cause such differences were due is uncertain. If there 

 were a seasonal cause, no definite seasonal sequence could be made 

 out, owing to the irregular mode of occurrence of the seams. 

 Perhaps, however, the variation merely depended on the capacity 

 of the water for canning a load at the time of formation of any 

 particular seam, and this view was supported by the fact that a 

 thick peat-layer, Avhich occupied a definite stream-channel at the 

 eastern end of the section, was composed almost wholly of the 

 coarsest and heaviest vegetable remains ; in it twigs were ver}^ 

 abundant, but seeds and leaves were scarce. However these varia- 

 tions were caused, it was clear that the Barnwell seams represented 

 accumulations of vegetable debris washed from various parts of 

 the river-basin ; there was no indication that the peat was in the 

 position of growth. 



If we judge by the botanical evidence, climatic and ecological 

 conditions remained the same in the Cam basin throughout the 

 accumulation of the seams. Hence the plants obtained from 

 each horizon may be regarded as representing one and the same 

 flora ; but, lest future work should give a new significance to such 

 differences as existed between the floras of individual seams,. 

 these floras are enumerated separately in an appendix to this 

 paper. 



The plants enumerated on pp. 8-10, including those identified 

 by Mr. Reid,i constitute the Barnwell Flora up to date. 



Grenerally speaking, the species to which the fossils belonged 

 were determined, but occasionally a plant could be referred to its 

 genus only, either because of the inevitable incompleteness of the 

 Reid Collection, or on account of the bad state of preservation 

 of the specimens. Plants believed to be unrecorded previously in 

 the fossil state were noted, but the literature of the subject is 

 so scattered that records of some fossils may possibly have been 

 overlooked. 



A careful study of the plant-lists showed that the flora consisted 

 of several groups of plants which were dependent for their ex- 

 istence upon special climatic and ecological factors ; with the view 

 of obtaining an idea of the flora, as a whole, these plant-groups, 

 rather than the individual species themselves, are described. 



1 J. E. Marr, Q. J. G. S. vol. Ixxv (1919-20) p. 226. 



