104 PROF. J. LOGAN LOBLEY, F.G.S.^ F.R.G.S._, ON THE HISTORY 



producing mountain ranges, a formidable obstacle is raised against 

 animal migration. So also a wide area of waterless or desert 

 land will present a difficulty effectually preventing the further 

 travel of many species, and impeding the progress of many 

 others. Even a river may bound the habitats of species. Dr. 

 Eussell Wallace found that in the Upper Amazon Valley* 

 " several species of monkeys, birds and insects come up to the 

 south bank of the river, but do not pass it, while allied species 

 come to tlie north bank, which in like manner forms their 

 boundary." 



Again, there is the phenomenon of discontinuous areas of 

 distribution in which the same genus or even species may occur,_ 

 although the areas may be at great distances apart, without 

 appearing in the intermediate areas. Of these Dr. Wallace 

 says : — " The known and probable changes of sea and land, the 

 known changes of climate, and the actual powers of dispersal of 

 the different groups of animals, were such as would have enabled 

 all the now disconnected groups to have once formed parts of a 

 continuous series."t 



Thus a wide field of enquiry is opened, and for complete 

 results a very large amount of investigation and research will 

 be required. The results here given must therefore only be 

 regarded as partial, approximate, and very incomplete. 



Geogkapiiical Changes. 



Since the fauna of Euiiope has been ruled and regulated,, 

 advanced and retarded, by geographical changes, a brief sketch 

 may be here given of these changes of land and sea in the 

 Pahrarctic region during recent geological times, so far as they 

 appear to be indicated by geological and biological considera- 

 tions. 



This part of our subject has received considerable illumination 

 from the work of Professor Hull, v»'ho, in papers to this. 

 Institute and elsewhere, has shown from soundings off the 

 European coasts the former extension westwards of our 

 continent. By this extension the south-west of Europe, or 

 what is now Spain and Portugal, was united to England and 

 Ireland, giving direct land communication with the south-west 

 of our sister island, or what is now the County Kerry. The 

 land area would then be so continuous that the P)ritish 

 Islands would be part of the Continental area, and where is now 



Island Life^ cliap. ii, p. 18. 



t Ihid.^ chap, iv, p. 70. 



