i8 9 3. EFFECT OF GLACIAL PERIOD. 265 



and hawkweeds, wafted by the wind, others, like goose grass, burdock, 

 and common Avens, adhering to the fur and wool of animals, others 

 carried by frugivorous birds, or adhering to the beaks and feet of 

 others, etc. — it would be strange if most of them did not migrate more 

 than 15 yards a year. 



There is another consideration. The plants which must have 

 crossed the plain on the hypothesis of a restocking from the Continent 

 after the Glacial epoch, include apparently some of the most slowly 

 spreading forms. 



While, then, the above considerations seem to indicate that our 

 present flora and fauna did not necessarily migrate across an eastern 

 plain after the Glacial period, they need not be taken as an argument 

 against the existence of such a connection, if that is supported by 

 other facts. There may have been such a connection, and yet our 

 plants and animals may have existed pretty nearly as they are now 

 before its existence. If it can be shown, on the one hand, that the 

 absent species are such as ought to have migrated across a land 

 connection, then the present distribution favours the view that our 

 country was not restocked from the Continent after the Glacial period; 

 if, on the other hand, they are species whose line of geographical 

 distribution did not extend so far west as our east coast, or so far 

 north as our south coast, then their absence is no argument either 

 way ; and if our country was not restocked from the Continent in post- 

 Glacial times, then the pre-Glacial flora and fauna must have survived 

 to a large extent. 



The existence of several species of South European plants in the 

 south-west of Ireland which are absent throughout the rest of Britain 

 also furnishes an argument in favour of survival ; for in the absence 

 of a direct land connection between Ireland and the north of Spain since 

 glaciation — for which there is no independent evidence — it is difficult 

 to understand how they can have got there. It seems on the whole a 

 more reasonable supposition that in the warm period preceding the 

 Glacial they were widely dispersed over Britain, and that they were 

 exterminated everywhere, except in the warmest corner, viz., the 

 extreme south-west of Ireland, by the cold. Such was the opinion 

 expressed by Professor Forbes. 5 At the same time the possibility of 

 a post-Glacial migration by other means than a land connection — as, 

 for example, by the carriage of seeds by migratory birds — must not be 

 lost sight of. 



A recent discovery which seems to hint that a part of our flora, at 

 least, is a survival, is that of the seeds of Naias marina in the Cromer 

 Forest Bed. The only British locality for this plant is Hickling Broad, 

 Norfolk, and hitherto the Forest Bed is the only fossil locality. It 

 would be, to say the least, a curious coincidence if it had been 

 exterminated by the ice and had then re-migrated from the Continent 



: ' Mem. Gcol. Survey, vol. i. 



