They are coral islands of comparatively recent elevation, and in no place rise more than 250 ft.
Oceanic islands are divided according to their geological character into volcanic islands and those of organic origin, including coral islands.
Next to these come the coral islands Nomuka and Lifuka in the Hapai group; Tofua, 2846 ft., Late or Lette, 1800 ft.
In the region of tropical hurricanes the navies, while in the Mediterranean and in the Indian Ocean converging wind system of a circular storm causes a heaping many soundings were made in connexion with submarine up of water capable of devastating the low coral islands of the cables to the East.
Pure calcareous sand and calcareous mud are formed by wave action on the shores of coral islands where the only material available is coral and the accompanying calcareous algae, crustacea, molluscs and other organisms secreting carbonate of lime.