322 SCIENCE PROGRESS 



represents a warm interglacial stage, showing a very different 

 set of conditions from the beds above containing Salix polaris 

 and other arctic plants, and the events which would produce 

 such a total change in the flora in the south of England must 

 have been widespread. The suggestion made by Lamplugh (12) 

 that the arctic flora might have lingered on and reinvaded the 

 area formerly occupied by a temperate flora without any wide- 

 spread change in conditions is surely due to a misconception of 

 the present distribution of these plants. 



It is quite certain that Salix polaris, S. herbacea, S. myrsinites y 

 Betula nana, and such temperate plants as Rhamnus frangula, 

 Rttbus Idwus, Rosa canina, Sambucus nigra, Corylus avellana, 

 Taxus baccata, did not grow at the same time over the low- 

 lands of the south of England. Whether the precipitation 

 during the deposition of the arctic bed was great enough to 

 produce glaciation on elevated ground in the north of England 

 and Scotland the plant deposits do not tell us, but we may be 

 certain that an arctic climate prevailed at that time. If, then, 

 from its position upon the chalky boulder clay, the Hoxne 

 temperate bed is older than the Lower Forestian in the peat 

 mosses, it carried the alternation of temperate and arctic phases 

 to a still earlier stage — though a stage which all will agree is 

 later than the last ice-sheet. It is true that evidence of actual 

 glaciation can only be given by glacial deposits, but changes of 

 temperature must be reflected in fossiliferous deposits. 



The Relation of the Strata to the Glacial Succession. — It is 

 evident that the peat mosses do not give any information 

 about the chain of events during the maximum glaciation of 

 the country, and it is immaterial whether we regard the 

 morainic material — upon which so many of the older peat 

 mosses in the south of Scotland rest — as the deposits of the 

 waning ice-sheet of maximum glaciation, or as the deposits of 

 an entirely distinct glacial stage separated from the ice-sheet 

 by a warm inter-glacial phase. The fact remains that the first 

 arctic bed contains an arctic-alpine flora which existed over 

 wide areas near sea-level. It is, of course, impossible from 

 the evidence of the plants to say whether all traces of glaciation 

 had vanished from Britain at that time or whether certain 

 regions were still under ice. An entirely different flora makes 

 its appearance in the Lower Forestian ; not only are all arctic- 

 alpine plants absent, but the flora is made up of well-grown 



