507 
CHAP. XXIV.] 
SUMMARY AND CONCLUSION. 
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 day. 
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, however, 
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 
