82 CARL H. LINDROTH 



not have been biologically effective, if the trans-Atlantic land connection is 

 removed entirely to Tertiary, Early Tertiary, or even to Cretaceous time, i.e. 

 to periods with a warm-temperate climate also on the North Atlantic islands 

 (Schwarzbach, 1955, p. 101, etc.). 



The most satisfactory explanation of present faunal and floral conditions in 

 Iceland (and Greenland) would be to assume that the Tertiary biota were 

 destroyed and followed by a new invasion from Europe. It is difficult to 

 imagine such a total destruction by any other agency than a glaciation. 



According to this hypothesis, the land connection Greenland-Iceland- 

 Scotland persisted (or was re-established) in at least one of the Interglacial 

 periods, offering an immigration route for Boreo-Temperate biota from 

 Europe. It is known from plant fossils that the climate of Iceland was slightly 

 warmer than now during at least one Interglacial period (with Pinus and 

 Picea in deposits). It was with some hesitation referred to the "Giinz-Mindel" 

 by Askelsson (1960). Alnus appeared in the "Mindel-Riss" Interglacial 

 (Thorarinsson, 1958). During the last Interglacial, the "Riss-Wurm", at least 

 Betula trees grew on the island (Thorkelsson, 1935). 



I am perfectly well aware that the hypothesis here emphasized (and 

 maintained also earlier: Lindroth, 1931, p. 551; 1957, p. 253, etc.) is against 

 the opinion of almost all geologists. It would be interesting to live long enough 

 to see how close to the truth it may be ! 



Since every idea of a North Atlantic land-bridge in Post-glacial time, 

 previously assumed by some older authors (e.g. Simmons, 1905), is a geological 

 impossiblity, the hypothesis stressed above implies that the main part of the 

 indigenous fauna and flora of the North Atlantic islands survived at least 

 one glaciation in situ. In this respect, conditions in Iceland are more easily 

 understood than in Greenland and have been treated by many biogeographers. 



As usually, only the effect of the Last Glaciation (WUrm) can be recon- 

 structed with some claim of reliability. 1 would like to add one more reason to 

 those proposed by several specialists in favor of a "WLirm-hibernation" in 

 Iceland: A deposit is known at Elhdavogur (near Reykjavik) from the 

 "Riss-Wiirm" Interglacial (Thorkelsson, 1935). It contains fragments of 

 seven beetle species, six of which are members of the present indigenous fauna 

 of the island; the remaining one is a species of flying water-beetles, genus 

 Hydroporus, unidentifiable as to species, but apparently not identical with the 

 single present representative of this genus in Iceland, H. nigrita F. Of the six 

 species in common with the present fauna, three are flightless, i.e. Nehria 

 gyllenhali Schnh., Pterostichus diligens Sturm, and Tachimts corticinus Gr. Is it 

 really within the limits of probability to assume that the Riss-Wiirm Inter- 

 glacial fauna of Iceland was exterminated to be substituted later, in Post- 

 glacial time, by oversea immigration by the very same, in part flightless, 

 species? To accept this would, for me, be a clear underestimation of the 

 random character of long-distance dispersal. 



