58 MR FRANCIS J. LEWIS 



Forestian. If that be so, the arctic bed at Hoxne might still be contemporaneous with 

 the first arctic bed of the peat mosses. 



There can be little doubt that the lower bed at Hoxne 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 Lampltjgh (12) that the arctic flora might have lingered on and re-invaded the area 

 formerly occupied by a temperate flora without any widespread 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, Betula nana, 

 and such temperate plants as Rhamnus Frangula, Rubus Idmus, Rosa canina, Sambucus 

 nigra, Corylus Avellana, Taxvs baccata, did not grow at the same time over the 

 lowlands 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 carries 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. 



A large amount of work has been done on the Continent since the first discovery by 

 Nathorst in 1870 of the remains of an arctic flora in fresh- water clays near Alnarp in 

 Sweden* (13). A great number of observations on such plant beds have been made 

 since then, not only by Nathorst, but by other observers in Sweden, Norway, Denmark, 

 Germany, and in Switzerland. The importance of the study of such stratified deposits 

 before we can understand the climatic fluctuations of the Pleistocene and the modern 

 distribution and character of the flora, has been fully recognised in those countries. In 

 Canada and the United States hardly any work on the succession of the flora has been 

 attempted, although those countries contain extensive peat deposits. The Bulletins of 

 the U.S. Geological Survey contain many records of peat deposits which from their 

 position in relation to the drifts and their geographical situation promise much interesting 

 material towards the history of changes in the distribution of the flora. 



If the birch zone of Sweden is contemporaneous with the Lower Forestian of 

 Scotland, as I suggested in 1906 (3), it is interesting to notice that the oldest forest 

 zone in both countries consists of birch. But it is impossible to say whether the spruce 

 and oak zones recorded from Sweden represent all the peat lying between the 



* I should have made it clear in Part II. that the first discovery of Arctic plant beds in Sweden was made in 

 1870, and was entirely due to the investigations of Nathorst. These investigations were of course made in Sweden 

 and not in Norway, as was inadvertently stated in Part II. A sketch of the investigations made up to 1891 is given 

 by Nathorst in the paper referred to above (13). 



