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CARL H. LINDROTH 



iso- and/or eustatic movements effecting positively the rise of a North Atlantic 

 land connection: The Palearctic element of the Greenland -Iceland biota, the 

 history of which we are here trying to trace, is not Arctic, not even Sub- 

 Arctic; the insects, at least, are members of a Boreo-Temperate fauna. 

 Therefore, they must have immigrated, not during a Glacial, but an Inter- 

 glacial period, possibly in Preglacial time. 



Since iso- and eustatic changes of the sea level fail to explain the assumed 

 land connection, the remaining possibility is that it was created by tectonic 

 movements within the area, or — more adequately expressed — that continuous 

 land once existed but was broken down by tectonic processes. 



This is perhaps more than a mere hypothesis. From northern Ireland and 

 western Scotland over the Faeroes, Iceland, and Greenland west to Disko 

 Island in Davis Strait runs a chain of volcanic rock-occurrences, mainly 

 basalt, formed in Tertiary time (Fig. 5). Whether these are remnants of a 



Fig. 5. Tertiary volcanic rock (mainly basalt) of approximately similar age in the 

 North Atlantic area. (Compiled from different sources.) 



continuous land area occupying large parts of the present North Atlantic 

 region, is still a matter of dispute (Einarsson, 1961), but some geologists 

 (e.g. Schwarzbach, 1959, pp. 32, 36) think it is probably so. 



The crucial question from the point of view of a biogeographer is how 

 long the assumed land connection existed. To geologists, this question is of 

 subordinate interest and only few of thein have tried to provide an answer. 

 Schwarzbach and Pflug (1957, p. 296) do not think that connection between 

 Iceland and the British Isles was probably after Eocene, and later, Schwarz- 



