

^'' 



*< 



t 





^Nl 



"%:' 



^ 1 



579 



CHAPTER XLIX. 



FOEMATION OF COEAL EEEFS. 





GEOAVTH OF CORAL CHIEFLY CONFINED TO TROPICAL REGIONS — PRINCIPAL 

 GENERA OF CORAL-BUILDING ZOOPHYTES — THEIR RATE OF GROWTH SELDOM 



THAN 



■ATOLLS OR ANNU- 



LAR REEFS WITH LAGOONS — MALDITE ISLES — ORIGIN OF THE CIRCULAR FORM 

 CORAL REEFS NOT BASED ON SUBMERGED VOLCANIC CRATERS — MR. DAR- 

 WIn's THEORY OF SUBSIDENCE IN EXPLANATION OF ATOLLS, ENCIRCLING 

 AND BARRIER REEFS — WHY THE WINDWARD SIDE OF ATOLLS HIGHEST — SUB- 

 SIDENCE EXPLAINS WHY ALL ATOLLS ARE NEARLY ON ONE LEVEL ALTER- 

 NATE AREAS OF ELEVATION AND SUBSIDENCE — ORIGIN OF OPENINGS INTO 



THE LAGOONS SIZE OF ATOLLS AND BARRIER REEFS — OBJECTION TO THE 



THEORY OF SUBSIDENCE CONSIDERED — COMPOSITION, STRUCTURE, AND STRA- 

 TIFIED ARRANGEMENT OF ROCKS NOW FORMING IN CORAL REEFS LIMB 



WHENCE DERIVED SUPPOSED INCREASE OF CALCAREOUS MATTER IN MODERN 



EPOCHS CONTROVERTED — CONCLUDING REMARKS. 



m 



structure of tlie earth's crust are most conspicuously displayed 



anim 



We 



may 



operation of these zoophytes in the ocean to the effects pro- 



smaller 



generate peat. In the case of the Sphagnum^ the upper part 



mineral 



mass^ in which the traces of organisation remain when life 

 has entirely ceased. In corals^, in like 



manner 



more 



durable materials of the generation that has passed away 

 serve as the foundation on which the living animals continue 

 to rear a similar structure. 



The stony part of the lamelliform zoophyte may he likened 

 to an interna] skeleton; for it is always more or less sur- 

 rounded by a soft animal substance capable of expanding 

 itself; yet, when alarmed, it has the power of contracting and 

 drawing itself almost entirely into the cells and hollows of 

 the hard coral. Although oftentimes beautifully coloured in 

 their own element, the soft parts become when taken from 



p p 2 



# 



