PREFACE. XIX 



maintain the struggle for existence; and have survived to the present 

 day, and form a tropical outlier, of which we have no other terrestrial 

 instances, but which is exactly parallel with the northern outliers of 

 arctic marine life which occur in our British Seas. 



Here, when the bed of the glacial ocean was upheaved, that upheaval 

 raised above water only such portions of it as had been formed at a 

 moderate depth. The deeper tracts were still under water, and there the 

 arctic forms would still live on, while climatal changes altered the 

 zoological character of the shallows of our seas. So with our land flora. 

 When the change of level connected the group of glacial islands, which 

 stood out from the sea, crowned with the Scandinavian flora, now the 

 mountain tops of Scotland, the original vegetation was preserved and 

 survived in isolation ; while on lower ground, the newly exposed land was 

 covered with a new temperate or Germanic flora. ' Mutato nomine' for 

 boreal marine outliers, read tropical terrestrial outliers, and the history of 

 the biological isolation of the Dead Sea is solved at once. 



The slight admixture of Indian types may be explained when we 

 consider that at that time, with a continuous Meiocene continent north of 

 the line, species would have a wider range than at present, and could 

 migrate and spread without check. Since the change in the coast outline, 

 some species may have become segregated in one part, and others in 

 another. The glacial action must have affected the temperature of 

 regions far beyond the reach of its actual glaciers and icebergs, and many 

 species must have retired to the South, or perished utterly. The 

 modifications of Ethiopian and Indian types, of which the avifauna 

 presents several instances, may yet be found in Arabia, the interior of 

 which is still to us a zoological blank. If absolutely peculiar, they must 

 either be the descendants of species which inhabited the country with 

 only a limited range prior to the glacial epoch, or are developments or 

 variations of other species stereotyped through long isolation. Consider- 

 ing, however, their co-existence with other unchanged forms, and the 

 comparatively recent date, geologically speaking, of the glacial epoch, the 

 former would seem to be the more probable solution. 



The fluviatile fishes claim special attention, dating, as they probably 

 do, from the earliest time after the elevation of the country from the 

 Eocene ocean. In the Foramenifera mentioned above as found in the 



