272 CHAPTER III 



Aube, Tachinus corticinus Gr., Byrrhus fasciatus Forst.),^ all of them members of 

 the present Icelandic fauna (Thorkelsson, 1935). 



The powers which may have affected displacement of the shore-line in favour 

 of the extension of land in the North Atlantic area are eustatic, isostatic, and tectonic 

 movements. 



(a) Eustatic movements of the sea, implying a world-wide change of the water 

 volume of the oceans, in Pleistocene time were caused first and foremost by the 

 glaciations. Part of the precipitation was stored on land in the form of glaciers and 

 thus withdrawn from the oceans, the level of which sank correspondingly. Cal- 

 culations of the vertical amount to which this happened are, as a matter of course, 

 highly diverging. They depend entirely on the estimated simultaneous volume 

 of all glaciers of the world during a certain phase of a glaciation. For the maximum 

 of the last glaciation (Wiirm, Wisconsin) the figures are usually given as something 

 between 90 and 100 meters (Zeuner, 1950, p. 129; Woldstedt, 1954, p. 289). 

 During the last but one, the '' great glaciation" (Riss, Illinoian), the regression of the 

 sea must have been more extensive but it cannot have amounted to more than one 

 fourth of the vertical distance necessary for realizing the postulated Scotland- 

 Greenland bridge. It may have contributed to its rise but was not alone responsible 

 for it. 



Eustatic regression of the sea is perfectly and positively connected with glacia- 

 tion (seen from a global point of view). Though this did not necessarily have its 

 maximum extension contemporaneously everywhere in the Northern Hemisphere, 

 countries situated as far north as Iceland and Greenland can never have remained 

 climatically unaffected by the ice during a glacial period. This means that, if eusta- 

 tic regression has played a part in the existence of the Scotland-Greenland bridge, 

 this must have been realized during a period of arctic or at least subarctic climate on 

 the islands considered. This assumption may seem tempting because, if so, the 

 faunistic barrier between Greenland and Baffin Island could be explained as a 

 barrier of ice. Facts, however, argue against this. The coleopterous fauna of 

 Iceland contains one single arctic species, the Water-beetle Colymbetes dolabratus 

 Payk., immigrated from a western direction. The rest of the indigenous fauna is 

 boreal, not even subarctic; many of its members do not ascend to timber limit 

 anywhere on the earth. Among the Coleoptera of Greenland there are only two 

 Palaearctic species, the Staphylinids Atheta hyperborea Brund. and Gnypeta cavi- 

 collis J. Sahib., which may be termed arctic; both are winged. 



A satisfactory explanation of these conditions is found only in the assumption 

 that the Scotland-Greenland land-bridge existed during a time of boreal climate and 



^ In addition unidentified fragments of a Hydroporus, not living in Iceland of today. 



