LIFE AT AND NEAR SURFACE 139 



In many places these coral trees and the 

 more massive rocky corals grow upwards until 

 they reach the surface of the sea, and in nu- 

 merous parts of the West Indies and in other 

 warm latitudes one may actually walk about 

 among these wonderful growths at low water. 



When the corals thus reach the surface, or 

 to within a short distance of it, they form the 

 so-called coral-reefs and in many places they 

 are a great menace to ships. The largest of 

 all coral-reefs is the Great Barrier Reef off 

 the western coast of Australia where, for hun- 

 dreds of miles, the corals grow by countless 

 millions and are exposed at low water, form- 

 ing a veritable wonderland for any one inter- 

 ested in marine life. 



Although such reefs are dangerous to mari- 

 ners, yet they are very useful as well, for they 

 break the force of the sea and waves and pro- 

 tect the shores and in many places ships find 

 safe anchorages from storms in the shelter of 

 coral-reefs. In this way one of the greatest 

 dangers of the sea may be utilised for man's 

 advantage and protection. 



Where these coral reefs are exposed to the 



