20 THE STORY OF LIFE IN THE SEAS. 



tion of the sea-bottom is often very great indeed 

 in shallow water, though it varies considerably 

 in different parts of the world. In the neighbour- 

 hood of the British coast, for example, the sea- 

 bottom is, in many places, carpeted with the 

 calcareous Sea-weed, Lithothamnion, in other 

 places the dredge will come up crammed full of 

 bivalve shells. But such instances as these in 

 which the floor of the sea is covered with animal 

 or vegetable shells, are comparatively rare and of 

 small extent in the neighbourhood of land in the 

 Temperate regions, and in nearly all localities the 

 true terrigenous deposits can be readily obtained 

 by the use of a small meshed dredge. In the 

 warmer regions of the world, however, the sea- 

 bottom in the shallow water is over great areas 

 completely covered by animal and vegetable 

 products. In the West Indies, and in some 

 parts of the Eastern coasts of Tropical America, 

 in the Eastern Archipelago and the coast of 

 East Africa and its islands, Coral reefs are found. 

 These are entirely built up of the skeletons and 

 shells of animals, and a few Coralline Algae. In 

 the vicinity of these reefs the floor of the sea 

 is for miles carpeted with the broken-down 

 skeletons of these animals, sometimes in the 

 form of a fine coralline sand, sometimes of large 

 lumps studded with knolls of living Corals, 

 Molluscs, Sea-urchins, and other creatures. We 

 find, therefore, in the warmer regions of the 

 world immense areas of shallow water in which 

 the terrigenous deposits take but a very small 

 part in the formation of the sea-bottom, animal 

 and vegetable life being so vigorous and active 



