Chapter IX — 151— On Migration 



order to understand the history of our contemporary floras, of greatest 

 significance are those climatic changes which took place during the 

 Tertiary period and during the glaciation of the northern hemisphere at 

 the beginning of the Quaternary period. 



The transition from the Cretaceous to the Tertiary period was ac- 

 companied in many parts of the globe by the uplifting of mountain 

 chains and the elevation of submerged land above the surface of the 

 sea. Precisely at this time there were formed the greatest of our 

 mountain systems: the Alps, the Himalayas, the Caucasus Mts., and 

 the North American Cordilleras. During the entire Tertiary period 

 there occurred changes in climatic zonation, leading to corresponding 

 changes in the vegetation zones. The most striking evidence of the 

 grandiose changes that took place during the Tertiary period are the re- 

 markable findings of Cretaceous and Tertiary fossil remains in the 

 Arctic. Where now stretch the arctic tundras there formerly grew 

 deciduous forests associated with a temperate climate. 



The finding in the Arctic of fossil remains of many genera now 

 distributed in the temperate zones does not, however, sufiice to prove 

 that in the past tropical climatic conditions prevailed in the Arctic, as 

 Heer has presumed. That they do not so suffice is confirmed by 

 Gothan's report (191 5) that he found in the wood of Cretaceous 

 conifers distinct annual rings (found also subsequently in fossil Ter- 

 tiary wood), which testifies to the existence in the Cretaceous period of 

 alternating cold and warm seasons. In this connection Berry's 

 conclusions are of interest (1930, p. 29) : — 



"There is no unequivocal botanical evidence of tropical or subtropical climates at any 

 time in the Arctic. There is no evidence from paleobotany of a lack of climatic zonation 

 at any geological period from which fossil plants are known, although at such times the 

 evidence points to a relative mildness and a lack of sharp zonation, as compared with the 

 present". 



This viewpoint of Berry's is supported by Kryshtofovich (1929, 

 1933), on the basis of his numerous investigations of the fossil vegeta- 

 tion of Asia, particularly his study of a collection of fossil plants from 

 the Lozva River in the northern Urals (61° 10' N.). The species com- 

 position of the latter flora has led him to believe that this flora must 

 have required for its existence a mean annual temperature of about 

 10° C. He further assumes — based on the finding in Eocene and Oli- 

 gocene deposits in the southern part of European U.S.S.R. (and even 

 more in western Europe) of fossil remains of such plants as Nipa and 

 Sahal pahns— that at 50° N. in southern Russia the temperature must 

 have been not less than i8°-20° C, while in western Europe on the 

 same parallel it might have been still higher, corresponding, therefore, 

 to subtropical or even tropical climatic conditions. 



As regards the Tertiary flora of Asia, Kryshtofovich states the 

 following (1929, p. 307): — 



"Turning now to the Tertiary Siberian floras we are not able to find in them any re- 

 mains that would permit us to suggest the existence anywhere in this country of strictly 

 tropical or subtropical conditions during the Tertiary period. On the contrary all the 

 known facts concerning the territory which stretches from Turgai and Tomsk on the west 

 to Vladivostok, Corea and SakhaUn on the east, demonstrate the former distribution there 

 of a flora composed mostly of temperate types such as Fagus, Ulmus, Alniis, Betula, Cory- 



