248 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. Lxvi. 



available, the expatriated vegetation gradually returned — 

 the flora proper to tlie margin of the snow being the first 

 to arrive, and then the other floras, rank behind rank, in 

 reverse order to that which they followed when their 

 exodus took place at the commencement of the Age of 

 Snow. Most of this repatriation probably took place in 

 the southern parts of Britain before the maximum limit 

 of depression was reached, and long before the subsequent 

 movement in the opposite direction commenced. 



It is well to bear in mind, in this connection, that there 

 is a large area of shallow sea around the south-western 

 parts of Britain, and that, in the transition period while 

 the depression was still in progress, there was still a land 

 communication across what is now the English Channel, 

 as far as the Pyrenean and Armorican regions beyond. 

 Likewise there was still land communication with the 

 Continent at the southern part of the North Sea, 



I see no difficulty whatever, while bearing these facts in 

 mind, in accounting for the extension of Pyrenean and 

 Armorican plants, by way of the land route referred to, as 

 far as Devonshire and Cornwall, or even to the south-west 

 of Ireland. It is mainly a question of time, if the land 

 communication be kept open ; and even when the sub- 

 mergence had gone so far as to admit the sea, the earlier 

 stages of that geographical phase were equally suitable for 

 the transport of the seeds by flotation, by the iunnigration of 

 mammals, and by the transportation effected by birds, etc. 



What has long been a cause for wonder with many 

 geologists is, not how it has happened that a few plants 

 have found their way from the Pyrenean areas to Ireland, 

 but why it is that there were not more. 



The whole history is one that teems with interest to 

 every student of biology. It is a most remarkable fact, 

 that a whole temperate flora, after long banishment from 

 an area whore its place has been held for perhaps hundreds 

 of thousands of years by Tundra and Steppe floras, should 

 have been repatriated without showing any marked evi- 

 dence of change, and should have almost entirely retaken 

 possession of the land, with only a few of the invaders left 

 to tell of the changes that happened during the term of 

 banishment of the former occupants of the land. 



