14 



phenomena to those still displayed in the arctic regions, bounded 

 in one part by snowy hills, and studded in another with ice-girt 

 islands. Once these the flora of the area in question would 

 easily be transported, by natural agencies, from what are now the 

 mountain ranges of Scandinavia, to those outposts on the moun- 

 tains of Great Britain which they at present occupy. Conveyed 

 in this way from island to island, borne on the bosoms of float- 

 ing icebergs, the wings of stormy winds, and by wandering arctic 

 sea-birds, they would first reach the higher islands which the 

 Grampians then constituted, and where they still grow in greater 

 plenty and variety, with a more decidedly arctic character than 

 elsewhere in the kingdom. Thence carried in a similar manner, 

 they would subsequently reach the lower islands of Scotland, 

 N. England, and Wales, now elevated into mountainous regions. 

 It would, however, for the most part, be only such plants as grew 

 upon the shores or lower slopes of the insular Grampians that 

 would thus be transported to those other and lower islands, and 

 find congenial habitats at a similar altitude to their native one. 

 Accordingly we find that the alpine flora of these, except upon 

 the very summits of the loftier peaks and ridges, is chiefly of a 

 much less arctic character than that of the Grampian range. 

 This cannot be adequately explained by difference in temperature 

 and elevation, for on many of the lower and more exposed peaks 

 of the Grampians we find some plants which grow only at much 

 higher elevations upon their neighbours. Such a phenomenon 

 evidently depends on the circumstance that in the one case, the 

 means of their dissemination were close at hand, and in the other 

 more remote or entirely absent. In this way the presence of 

 identical species at such distant points, which otherwise could not 

 be satisfactorily accounted for, is readily explained, and their 

 original derivation and present diffusion are no longer enveloped 

 in mystery. 



The theory, therefore, which we have thus briefly stated and 



