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OCEANIC ISLANDS. 
Apr., 1890. 
OCEANIC ISLANDS : 
SOME ACCOUNT OF THE PROBLEMS PRESENTED BY THE 
STRUCTURE AND NATURAL HISTORY OF ISLANDS 
NOT IMMEDIATELY ADJACENT TO ANY CONTINENT.* 
BY REV. T. S. LEA, M.A. 
An oceanic island may be defined as above, to the exclu¬ 
sion of all islands accidentally severed from a neighbouring 
continent by narrow and shallow seas. Of the latter class 
the British Islands are a good example, as there is no great 
depth of water in the Straits of Dover, and no break in the 
geological formation. Moreover, when the natural history of 
Britain is compared with that of the rest of Europe, it is 
found that there are scarcely more than two plants and a 
very few insects which are not also to be found in some part 
of the Continent. The general facies of the flora and fauna 
on both sides of the Channel is identical. 
On the other hand, when such islands as the Canaries or 
Madeira come to be investigated, they are found to differ 
from Great Britain in both those respects. Their geology is 
not the same as that of the continent of Africa, and their 
flora and fauna are to a large extent peculiar. 
In the present state of geological investigation it seems 
probable that the main oceanic areas have been practically 
permanent throughout the world’s history. There are 
distinct arguments against any such theory as that which 
the story of Atlantis has suggested, that a great continent 
has subsided within times known to man. One of these 
arguments is the structure of such islands as those which 
will be chiefly mentioned in this paper. 
The oceanic islands of the world group themselves under 
two main divisions—coral islands and volcanic islands. 
Dismissing the former as being a subject in themselves for 
separate investigation, but referring in passing to Barbados 
as an instance of how change of level from geological causes 
may give some of these a greater elevation than that of a 
mere atoll, I may proceed at once to the volcanic islands. 
These may be found in all parts of the ocean. A chain of 
them passes down the Atlantic basin, and several important 
instances lie in the Pacific. The most prominent example is, 
perhaps, the Hawaiian group, for there the process both of 
construction and subsequent denudation is going on before 
*Read before the Birmingham Natural History and Microscopical 
Society, May 7th, 1889. 
