AGE OF COKAL REEFS. 177 



worn away from one part of the Reef help to 

 build it up elsewhere. The Corals forming the 

 Reef are not the only beings that find their home 

 there : many other animals Shells, Worms, 

 Crabs, Star-Fishes, Sea-Urchins establish them- 

 selves upon it, work their way into its interstices, 

 and seek a shelter in every little hole and cranny 

 made by the irregularities of its surface. In the 

 Zoological Museum at Cambridge there are some 

 large fragments of Coral Reef which give one a 

 good idea of the populous aspect that such a 

 Reef would present, could we see it as it actually 

 exists beneath the water. Some of these frag- 

 ments consist of a succession of terraces, as it 

 were, in which are many little miniature caves, 

 where may still be seen the Shells or Sea-Urchins 

 which made their snug and sheltered homes in 

 these recesses of the Reef. 



We must not consider the Reef as a solid, mas- 

 sive structure throughout. The compact kinds of 

 Corals, giving strength and solidity to the wall, 

 may be compared to the larger trees in a forest, 

 giving it shade and density ; but beneath these 

 larger trees grow all kinds of trailing vines, 

 ferns, and mosses, wild-flowers, and low shrubs, 

 filling the spaces between them with a thick un- 

 derbrush. The Coral Reef also has its under- 

 brush of the lighter, branching, more brittle 

 kinds, filling its interstices, and fringing the sum- 



8* L 



