~ THE SEA 359 
the relation of planets to the sun; as, for 
instance, the Cape de Verde Islands to Africa, 
Ceylon to India, or Tasmania to Australia. 
Secondly, Volcanic islands; and 
Thirdly, Those which owe their origin to 
the growth of Coral reefs. 
Fig. 49. — Whitsunday Island. 
Coral islands are especially numerous in 
the Indian and Pacific Oceans, where there 
are innumerable islets, in the form of rings, 
or which together form rings, the rings them- 
selves being sometimes made up of ringlets. 
These “atolls” contain a. circular basin of 
yellowish green, clear, shallow water, while 
- outside is the dark blue deep water of the 
Ocean. The islands themselves are quite low, 
with a beach of white sand rising but a few 
