THE EUROPEAN SEAS. 



Ill 



where they are, should be present in the southern 

 districts of the countries bounding the English 

 Channel — in the region of the Devonian flora, 

 where they are not. Nor can we suppose that they 

 have been conveyed as seeds through the air ; for 

 besides the important fact that they are all mem- 

 bers of families having seeds not well adapted for 

 such diffusion, and that the species of Composite, 

 and other plants with winged seeds associated with 

 them in Spain, are not present with them in Ire- 

 land ; it would be very extraordinary if the winds 

 which had conveyed them so far, had never, through, 

 probably, a long series of centuries, conveyed them 

 still farther, and diffused them in a country where 

 there are abundance of situations well adapted for 

 their habitation. 



"The hypothesis, then, which I offer to account 

 for this remarkable flora is this, — that at an ancient 

 period, an epoch anterior to that of any of the 

 floras we have already considered, there was a geo- 

 logical union or close approximation of the west of 

 Ireland with the north of Spain ; that the flora of 

 the intermediate land was a continuation of the 

 flora of the peninsula ; that the northernmost bound 

 of that flora was probably in the line of the western 

 region of Ireland ; that the destruction of the in- 

 termediate land had taken place before the Glacial 

 period ; and, that, during the last-named period 

 climatal changes destroyed the mass of this south- 

 ern flora remaining in Ireland, the survivors being 



