ACTINOZOA. 195 



surface of the reef into one continuous level, and 

 the alterations to which its dead and deeply-sub- 

 merged portions become exposed in the lapse of 

 time ; these, and other kindred subjects of inquiry, 

 fall rightly within the province of the geologist. 

 As monuments of past change. Coral-reefs form 

 the basis of some of the most " splendid general- 

 isations " which his science has deduced. For 

 him an island occupied each region where now 

 without interruption flow the quiet waters of a 

 lagoon. And seas must have once rolled over 

 those existing continents amid whose mountain- 

 chains remains of ancient Coral-reefs abound. 



Yet the zoologist, in taking leave of his own 

 department of this subject, cannot, without satis- 

 faction, contemplate how large a portion of the 

 earth's substance must, during the long lapse of 

 geological time, have formed part of the organised 

 structures of a group of beings who still continue 

 to fulfil, with no impairment of efficiency, the 

 great task for ages allotted them in the scheme of 

 universal nature. Not matter only, but force, he 

 sees made subject to their sway. The physical 

 agencies, which seemed at first to threaten destruc- 

 tion to the growing Coral, are soon successfully 

 overcome, and then pressed into its service. Nay, 

 without their aid, so much of the reef as rises 

 above the ocean level, forming the abode of plants 

 and animals, and finally of man, could not even 

 have existed. But had Coral-pol3rpes not pre- 

 viously laboured, the same forces would have been 

 potent only to destroy. 



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