170 THE OAK. 



in the Tertiary also, and we have to conclude that the 

 oaks were probably already a well-developed group of 

 plants before the higher mammalia existed i. e., so far 

 as we can judge from the fragmentary records of the 

 rocks. It seems that even the present species of oaks 

 were already in existence in Tertiary times, and possibly 

 some of their varieties also. 



From the evidence of their fossil remains, together 

 with the facts of their present distribution, it is at least 

 exceedingly probable that the European oaks, including 

 our English oak, came into existence somewhere in the 

 East, and that, after spreading from Asia towards the 

 West, they are now slowly retreating before competing 

 forms e. g., the beech. Meanwhile the English oak 

 (Q. Robur) has been giving rise to several varieties, of 

 which three at least (viz., pedunculata, sessiliflora, and 

 pubescens) have become sufficiently marked to be re- 

 garded as species by those who do not consider the con- 

 necting forms. 



It is not improbable that this migration of the Euro- 

 pean oaks from Asia was completed before the islands 

 of Sicily, Sardinia, Corsica, and Britain were separated 

 from the mainland of the Continent. Moreover, our 

 English oak is not distantly related to certain species 

 of Eastern Asia and of Western North America, and it 

 has been surmised that all these related forms sprang 

 from a common ancestor not unlike our English oak 

 of to-day. Again, fossil leaves from Italy, found in 

 diluvial deposits, are so like those of certain Californian 



