350 VNNALS NEW YORE ACADEMY 01 SCIENCES 



Myotics torquatus Halsbandleuiruing Banded lemming 



Canis lagopus Eisfuchs Arctic fox 



(into borealis Vielfrass Wolverine (glutton) 



I'n tori us < rin i inn Gr. Hermelin Ermine 



Arvicola nivalis Arctic vole 



Lagopus albus Moorsdnieelmuii Ptarmigan 



Asio palustris Sumpfeule 



Cygnus musicus Siii£scli\v;m 



Animals like the banded lemming adapted to extreme northerly condi- 

 tions generally cling to these very obstinately and perish rather than con- 

 form to an altered environment (Nehring). This species dwells imme- 

 diately to the north of the region of coniferous forests, among scattered 

 shrubs of the common juniper (Juniperus communis), the dwarf birch 

 (Betula nana), the polar willow (Salix polaris) and the mountain dryas 

 (Dryas octopetala). Thus we may be confident that the lemmings dis- 

 covered in Pleistocene times in England, France, Belgium and a large 

 part of Germany are proof of climatic conditions similar to those of the 

 present circumpolar region. We must conclude that the borders of the 

 ice caps were surrounded by tundra or barren ground conditions at sev- 

 eral Pleistocene stages. The lemmings probably dwelt in the immediate 

 neighborhood of the glaciers. The existing tundras are characterized by 

 frozen subsoil and the absence of trees or shrubs except along the river 

 borders. 



The reason for associating the woolly mammoth with this fauna is that 

 the mammoth as depicted by the men of the Postglacial Stage agrees pre- 

 cisely in its form, its proportions, and its hairy covering with the mam- 

 moths which have been discovered in the frozen subsoil of northern Si- 

 beria and are washing out in large numbers along the northern Siberian 

 and American coast at Eschholtz Bay and elsewhere. At Thiede near 

 Braunschweig, a classic locality, the lemming remains are associated 

 with those of the arctic fox, arctic hare, reindeer, musk-ox and mammoth. 

 Thus the comparison of certain regions of Pleistocene France and Ger- 

 many with arctic Eurasia and the barren grounds of northern Asia and 

 North America is based on the strongest evidence. 



MIGRATION THEORY OF FLORAS AND FAUNAS 



The principal contributors to the theory of northward and southward 

 migrations and to the succession of faunas and floras are Nehring (1880- 

 1896), Woldrich (1882-1896) and Penck (1896-1909). Such alterna- 

 tion is held by Penck to be demonstrated in Switzerland, where during 

 the Third or Eiss glaciation the woolly mammoth and woolly rhinoceros 



