122 TREE ANCESTORS 



temperate zone and a section Nothofagus for their antipodean 

 congeners. The latter have since been raised to generic rank, 

 quite rightly it seems to me, although their close relationships and 

 community of origin with the true beeches is clearly demonstrable. 

 The curiously segregated ranges of these existing forms is shown 

 on the accompanying sketch map. 



Granting that these two lines are offshoots of a common stock 

 the question of its original home at once suggests itself, along 

 with the query as to whether in some past time members of the 

 2 genera flourished side by side either in the north or the south tem- 

 perate zone. These questions can only be answered by an appeal 

 to the fossil record, a book wdth unfortunately many missing 

 chapters, especially those relating to the great land mass of Asia. 



The oldest known fossil forms are a species {Fagus prisca Ettings- 

 hausen) from the early Upper Cretaceous (Cenomanian) of Saxony 

 and three species in the Dakota sandstone of the western United 

 States of almost exactly the same age as the Saxon species. Their 

 essentially contemporaneous appearance in Europe and America 

 argues that they were immigrants into both regions from some third 

 area. Only two alternatives are probable. Either their ances- 

 tors came from the Arctic region and spread southward simulta- 

 neously into Europe and America or else they originated in Asia 

 and spread westward into Europe and eastward into America 

 across the land bridge which closed Behring Sea at about this 

 time. If the Arctic was the original home of the beech its remains 

 should occur in either the Cenomanian or later Cretaceous floras 

 of Greenland where it has not been found although it is present 

 in that region in the Tertiary. Furthermore if it had originated 

 in the north it should have been a member of that migratory wave 

 of vegetation that swept southward along the east coast of North 

 America at about the dawn of the Upper Cretaceous. Our east 

 coast Cretaceous contains a very large flora found in deposits of 

 this age from Marthas Vineyard to Alabama and this flora had a 

 great many elements in common with the Greenland Cretaceous 

 flora. No traces of Cretaceous beeches have, however, been dis- 

 covered along the Atlantic coast. 



