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migrated from the one to the other ; since they could no more 

 have been transmitted across the intervening lowlands, except by 

 some special agency, than they could have been transmitted, 

 except in the same way, across the waters of the German Ocean 

 from Norway to Scotland. Hence Forbes supposed that the dis- 

 tribution of this alpine flora was effected during the glacial 

 epoch, which, indeed, the very character of the plants themselves 

 point out as the most suitable. During this period, as substan- 

 tiated by various geological and physical phenomena, to some of 

 which we have referred in our sketch of Ben Macdhui, the moun- 

 tains of Great Britain stood forth as hilly islands in the Case of 

 the Grampians and the other higher peaks, Or as low -lying 

 islands in the case of the other and inferior groups, whose rocky 

 coasts were swept by an arctic sea and grinded by its icy waters. 

 In all probability, these were but members of a chain of islands, 

 vestiges of which are still preserved in those of Orkney and 

 Shetland, extending to the area of Norway through a glacial 

 ocean, and clothed with a boreal vegetation, which subsequently, 

 as the islands were gradually upheaved and the climate conse- 

 quently changed, became limited to the upper portions of the 

 new-formed and still existing mountains* This interesting- 

 theory thus carries us back for the origin and early diffusion of 

 our alpine plants, to an epoch now well known to and universally 

 recognised by geologists, when the climatal conditions of the 

 area under notice were such as to be admirably adapted for the 

 diffusion of a sub-arctic flora, destined to become afterwards an 

 alpine one, from its home in the parent north. Upon the 

 numerous and varied proofs for the former and protracted exis- 

 tence of such an icy sea extending over the whole of Northern 

 Europe, and southward even to the Alps and Carpathians, I need 

 not at present enter, as these are quite familiar to you all. For 

 the elucidation of our theory, all that is absolutely required is 

 simply to conceive of it as presenting somewhat similar physical 



