230 



UTILIZATION OP MINUTE LIFE. 



circumstance explains the frequency of their crater- 

 like forms (Fig. 28). Dalrymple says he has seen 



FIG. 28. Circular Coral Island, recently formed in the Pacific Ocean, prin- 

 cipally composed of the species Madrepora muricata, and shutting in a 

 portion of the ocean as a lake. 



madrepore banks in all their stages some in deep 

 water, others with a few portions above the surface ; 

 some just formed into islands without the slightest 

 vestige of vegetation ; others with a few weeds on 

 their highest point ; and, lastly, such as are covered 

 with trees of many years' growth, " with a bottom- 

 less sea at a pistol-shot distance." 



As soon as the edge of a reef is high enough to 

 lay hold of the floating sea-weed, to retain the 

 seeds of plants brought by the winds and currents, 

 or for a bird to perch upon, the "coral-island" 

 may be said to commence its existence. The ex- 

 creta of birds, wrecks of all kinds, feathers, cocoa- 

 nuts floating with the young plant out of the shell, 

 various grains, and sea- weeds, are the first elements 

 of the new island. 



