CHAr. xxiv.J SUMMARY AND CONCLUSION. 



507 



The conclusion is, on the whole, that the periods allowed by 

 physicists are not only far in excess of such as are required for 

 geological and organic change, but that they allow ample margin 

 for a lapse of time anterior to the deposit of the earliest fossili- 

 ferous rocks several times longer than the time which has 

 elapsed since their deposit to the present da}^ 



Having thus laid the foundation for a scientific interpretation 

 of the phenomena of distribution, we proceed to the Second Part 

 of our work — the discussion of a series of typical Insular Faunas 

 and Floras with a view to explain the interesting phenomena they 

 present. Taking first two North Atlantic groups — the Azores 

 and Bermuda, it is shown how important an agent in the dispersal 

 of most animals and plants is a stormy atmosphere. Although 

 900 and 700 miles respectively from the nearest continents, 

 their productions are very largely identical with those of Europe 

 and America ; and, what is more important, fresh arrivals of 

 birds, insects, and plants, are now taking place almost annually. 

 These islands afford, therefore, test examples of the great dis- 

 persive powers of certain groups of organisms, and thus serve as 

 a basis on which to found our explanations of many anomalies 

 of distribution. Passing on to the Galapagos we have a group less 

 distant from a continent and of larger area, yet, owing to special 

 conditions, of which the comparatively stormless equatorial at- 

 mosphere is the most important, exhibiting far more speciality 

 in -its productions than the more distant Azores. Still, hov\'ever, 

 its fauna and flora are as unmistakably derived from the 

 American continent as those of the Azores are from the 

 European. 



We next take St. Helena and the Sandwich Islands, both 

 wonderfully isolated in the midst of vast oceans, and no longer 

 exhibiting in their productions an exclusive affinity to one 

 continent. Here we have to recognise the results of immense 

 antiquity, and of those changes of geography, of climate, 

 and in the general distribution of organisms which we know 

 have occurred in former geological epochs, and whose causes 

 and^ consequences we have discussed in the first part of our 

 volume. This concludes our review of the Oceanic Islands. 



Coming now to Continental Islands we consider first those of 



