QUATERNARY DEPOSITS OF BRITISH ISLES — BROOKS. 363 



duration of interglacial periods in America. His estimates, compared 

 with those of Penck and Bruckner for the Alps, give : 



T. C. Chamberlin also, on the basis of age determination in 

 Europe and America, concludes that the glacial epochs in the two 

 continents were simultaneous (133). 



In one case at least, moreover, we seem to have direct evidence 

 for the continuous extension of a climatic period over a large part of 

 the Northern Hemisphere; I refer to the postglacial climatic opti- 

 mum, evidence of which has been found in Iceland, Spitzbergen, 

 Franz-Josef Land, the White Sea, Greenland, and North America. 



In Iceland, G. Bardarson (134) and H. Pjetursson (135) have 

 found raised beaches and marine deposits in the north and northeast, 

 indicating a submergence of about IT meters and containing Mol- 

 lusca which now live only on the south and southwest coasts, and 

 consequently indicating a climate warmer than the present. 



In Spitzbergen, Andersson (136) found a raised delta deposit with 

 flowering plants not now living on the islands, and A. S. Jenson 

 and P. Harder found raised beaches indicating a submergence of 10 

 to 25 meters and containing Mollusca {Mytilus edulis, Cyprma 

 islandica- and Litorma litorca) now extinct on the shores of Spitz- 

 bergen. 



In Franz- Josef Land, Nansen (137) found Mytilus edulis in an 

 old shore line at 10 to 20 meters, evidently of the same age. 



In the White Sea and Murman Sea, N. Knipowitsch (138) found 

 raised beaches with species of Cavdiwm now extinct there. 



In Greenland, A. S. Jensen (139) found in Orpigsuit Fjord a well- 

 marked warm period with the land about 10 meters below its present 

 position relative to the sea, and raised beaches containing Mytilus 

 edulis even north of 66^° N., and as far as Sophia Sound in northeast 

 Greenland, though its present northern limit in America is the 

 Newfoundland Bank. 



On the coast of Canada (Maritime Provinces) G. F. Matthew (140) 

 found evidence of a period of elevation, immediately preceding the 

 present epoch, when the climate resembled that of Middle New Eng- 

 land. 



In gravel terraces along the Niagara River, between the Whirl- 

 pool and Goat Island, A. P. Coleman (141) has found species of 

 Unio not now living in the Canadian lakes, but in the tributaries of 

 the Mississippi. The beds were formed during the last third of the 



