The relationship between the palaearctic and nearctic faunas 



271 







*«?- 



FIG. 43. The bottom configuration of the North Atlantic. The detailed figures give 

 greatest depth of the ridge or plateau between the islands. 



(From LiNDROTH, 1931, supplemented by Dr Borje Kullenberg, Gothenburg, in lift.) 



and Birds, especially of the Greenland fauna, but there is clear evidence in favour 

 of the view that subspecies formation is often a rapid procedure among Verte- 

 brates. The development into new "subspecies" of the Varying Hare, Lepus 

 timidus L., and the House-Mouse, Mus musculus L., on the Faeroes, both introduced 

 with man (Degerbol, 1940), is a good illustration. 



By a process of elimination we thus arrive at the opinion that the land connect- 

 ing Greenland and Iceland with Europe must have existed in Pleistocene time 

 and before the last glaciation (Wiirm, Wisconsin). This is also supported by the 

 present distribution of the Icelandic fauna which clearly indicates survival of 

 most of its indigenous members within two isolated glacial refuges in the south 

 and southeast (fig. 46; Lindroth, 193 1, pp. 489 a.f., 557-563). 



Another remarkable fact is the discovery, in a fossiliferous interglacial layer in 

 SW Iceland, of insect rests belonging to 6 species of Coleoptera {Nebria gyllenhali 

 Schnh., Patrobus septentrionis Dej., Pterostichus diligens Sturm, Agabus solieri 



