214 CORALS 



In the study <>f coral reefs we have a series of natural 

 phenomena and a number of biological and geological 

 problems which could only be dealt with adequately in a 

 separate volume or series of volumes. But an outline 

 sketch of them must be attempted here because they 

 represent one of the principal objectives to which the study 

 of the several classes of corals inevitably leads. 



We may look upon the Madrepores and the Millepores, 

 the Nullipores and the Astraeids, and even the Gorgonias 

 and the Foraminifera, as the bricks and mortar with which 

 the great mansions of the coral reefs are built ; and our task 

 is not complete if, having studied the bricks and mortar, 

 we do not consider the structure of the house as a whole. 

 Moreover, the coral reefs, like mansions, are inhabited, and 

 the study of the inhabitants — the fish, prawns, starfish, 

 worms, and many others — and their relation to the structure 

 which they frequent, cannot be entirely neglected even in 

 an introductory chapter on the greater subject. 



It may be remembered that, although the structures 

 known as coral reefs are confined to the w'aters of the 

 tropical belt, the corals have an almost world-wide dis- 

 tribution in the sea. Many examples of corals found within 

 the British area have been described. Tangled masses of 

 coral of great size are dredged up from some localities of 

 the Mediterranean Sea. The cold waters of the Norwegian 

 fjords yield a harvest of large massive corals of various 

 kinds, and in the great depths of the ocean where the 

 temperature is little above freezing-point, corals are often 

 found. 



But these corals occur usually as isolated individuals 

 or in relatively small patches, and it is only under the 

 tropical conditions of warmer water and more intense 

 sunlight that " when they are come to their full growth 

 there grow others between them and then upon these grow 

 others till it is become like a rock for thickness." 



The coral reefs are as varied in their contours, in their 

 composition, and in their distribution as the dry land itself, 

 and the customary classification of them into fringing reefs, 

 barrier reefs, and atolls is nothing but an artificial aid to 



