54 ANEMONES AND CORALS 



be highly aerated, pure, free from sediments, and contain an 

 abundance of living organisms : conditions that can only exist in 

 the neighbourhood of islands standing in deep water. Nor are the 

 reef-building Corals ever to be found at such great depths as those 

 at which some of the simple solitary Corals live, for the temperature 

 of the sea rapidly diminishes with depth, so that the 86 to 68 F. 

 necessary for the growth of the reef-builders is not maintained 

 beyond a depth of about 20 fathoms. Therefore, to see the 

 wonderful reef-building Corals of to-day, we must visit the warmer 

 waters of the Indian, Pacific, and Atlantic Oceans, and the 

 Caribbean Sea. 



Coral reefs are divided into three types : shore-reefs, which 

 fringe the shores of continents or islands ; encircling or barrier 

 reefs, which rise from deep water at a greater distance than the 

 shore-reefs from land, encircling an island, or stretching like a 

 barrier along the coast, like the wonderful reef which fronts the 

 north-east coast of Australia, with a length of nearly a thousand 

 miles, running parallel with the shore at a distance varying be- 

 tween twenty and seventy miles ; and atolls, or lagoon islands, 

 which are low reefs generally but a few hundred yards wide, 

 enclosing a lagoon. An atoll, or lagoon island, presents a most 

 wonderful sight, one that remains vividly impressed upon the 

 memory of the traveller for the rest of his life. As the ship 

 approaches the atoll, the voyager sees rising out of the deep blue 

 sea a low more or less circular belt of land dotted with feathery 

 crowned coco-nut trees. A white line of breakers fringes the 

 reef, thundering against it and sending up great spouts of spray 

 and foam, while within the encircling ring of Coral reef the quiet 

 waters of the lagoon shine like a burnished mirror. 



As one gazes at the mighty onslaught of the waves dashing 

 perpetually with cataract force against the low reef, one feels 

 that even the hardest rock must ultimately yield to such terrific 

 battering. " Yet," to quote Dr. Hartwig, " the insignificant 

 Coral islets stand and are victorious ; for here another power, 

 antagonistic to the former, takes part in the contest. The organic 

 forces separate the atoms of carbonate of lime one by one from 

 the foaming breakers, and unite them in symmetrical structure. 

 Let the hurricane tear up its thousand huge fragments, yet what 

 will this tell against the accumulated labours of myriads of archi- 





