QUATERNARY DEPOSITS OF BRITISH ISLES — BROOKS. 325 



tween two forest layers in Ross and in the Shetland Islands, but in 

 the Hebrides the upper forest layer is absent. 



Lewis's conclusions about the peat sections were confirmed by G. 

 Samuelsson, a Swedish geologist, who visited Great Britain in 1909 

 (102). He found the two forest layers separated by the arctic bed 

 and peat at several localities in Scotland. But in his endeavor to 

 correlate the Scottish peat mosses with the Swedish, Samuelsson 

 adopts J. Geikie's classification of the Scottish deposits, and regards 

 the 100-foot beach as contemporaneous with the Yoldia sea. He is 

 consequently obliged to correlate the cold 50-foot beach with the 

 warm Litorina sea, and to omit the 25-foot beach altogether. But 

 both 25-foot beach and Litorina sea appear to fall within the " post- 

 glacial climatic optimum," and to form part of a series of raised 

 beaches with warm fauna occurring on both sides of the North At- 

 lantic, in Greenland, Iceland, and even in the Arctic Ocean, which 

 will be referred to more fully later. The warm, dry upper forestian 

 ends in the bronze age, as does Blytt's warm, dry subboreal period, 

 but as the arctic bed corresponds to the last glaciation of north Eu- 

 rope, the lower forest bed must fall, not in Blytt's boreal period, 

 where Samuelsson puts it, but in the last interglacial of north Eu- 

 rope. Blytt's boreal period seems to be unrepresented in Britain, 

 but this is not surprising, for, as described later, it is also unrepre- 

 sented in the peat bogs of north Germany. 



My own views of the correlation of the Quaternary deposits of 

 Great Britain are shown in the following table : 



65133°— sm 1917 22 



