IX 



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 



