358 MR FRANCIS J. LEWIS 



The exact correlation of the deposits belonging to widely separated areas depends 

 upon the presence in each area of one or two well-marked datum lines, for a basal layer 

 of Arctic plants in one country can hardly be correlated with a basal layer of Arctic 

 plants in another without good evidence of the contemporaneity of the glacial deposits 

 upon which they rest. 



In conclusion, I wish to express my thanks to Dr Horne, F.R.S., for much valuable 

 help and advice during the progress of the work and for the use of many of the 

 Geological Survey maps dealing with the districts mentioned in this paper ; and to 

 Professor Geikie, LL.D., F.R.S., for many suggestions. 



I am also much indebted to Professor Trail, M.D., F.R.S., for determining some of 

 the willows. 



The scientific expenses of this investigation have been defrayed by a grant from 

 the Government Grant Committee of the Royal Society. 



LIST OF REFERENCES. 



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(2) Reid, Clement, "Origin of the British Flora," 1902. 



" Notes on the Geological History of the Recent Flora of Britain," Ann. of Bot., vol. ii., 1888. 

 "Flora of the Cromer Forest Bed," Trans, of the Norfolk and Norwich Naturalists' Soc, 

 vol. iv., 1886. 



(3) Lewis, F. J., "Plant Remains in the Scottish Peat Mosses," Part I., Trans. Royal Soc. Edin., 



vol. xli., part hi., No. 28, 1905. 



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