52 THE GREAT BARRIER REEF. 



conception of it may, however, be yained from the fact that rocks of tons' weight disappeared from their beds, 

 and stones, fully loolli. in weight, were thrown in masses fully 30 feet high. Volumes of water rose 50 feet 

 high, which the wind separated into spray and then disappeared as mist. Even the sea-birds were killed, and 

 trees, apparently of fifty years' growth, were snapped like carrots. The sea appeared to know no bounds, and 

 had it risen about 15 feet higher, the entire island w^ould have been submerged. The occurrence at Java being 

 still fresh in our memories we feared that this culminating catastrophe was about to happen. Had it done 

 so, none would have been left to tell this tale. The sea has now gone back and the sun re-appeared, leaving the 

 island strewn with wreckage. 



It is worthy of note, in association with the present plate, that a high bank of coral boulders 

 is thrown up among the vegetation, in the extreme background, to a considerable height above the 

 reach of the highest spring-tides, of which the vegetation marks the normal limit. This phe- 

 nomenon fully substantiates the record concerning the abnormal ingress of the sea embodied 

 in the foregoing account of the same disastrous cyclone. 



PLATE XXXII. 



SPECIMENS OF CORIL ROCK CONGLOMERITES. 



The special purpose of this plate is to illustrate the structural composition ot the bulk of the 

 material of which coral-reefs are composed. The multiform and multi-coloured coral-growths, 

 whose life aspects have been variously portrayed in a large number of the preceding plates, 

 represent a thin superficial crust that overlies a relatively' small and chequered surface of 

 the entire reef-mass. The solid basis upon which these corals grow, and the vast expanses of 

 solid coral rock that are accuinulated at a considerably higher plane than that wherein the coral 

 polyps can exist, is built up almost exclusively of the finely triturated detritus of the skeletons 

 of preceding polyp generations, combined with that of the calcareous shells of molluscs and other 

 lime-secreting organisms. The local tides and currents are a main factor in determining the 

 ultimate composition of this coral rock, sweeping the finer or coarser constituents into defined 

 areas when they become solidified m forms varying in aspect and texture from that of the finest 

 grained limestone and oolite to the coarsest conglomerate. The larger rock fragment illustrated 

 by Fig. 5 of the accompanying plate furnishes a very typical example of the character of the 

 main mass of the ordinary inshore or platform reefs that skirt the shore of every coral islet or 

 mainland-fringing reef, or that, again, composes the most elevated stratum of the innumerable 

 isolated reefs of the Barrier system that are awash at ordinary low tides. The specimen above 

 referred to was separated from one of the storm-detached masses of the platform reef at Rocky 

 Island. Its coinposition, as may be recognised on examination with a hand-glass, consists 

 mostly of minutely triturated coral and shell fragments less than one-eighth of an inch in diameter, 

 eroded, and subsequently so encrusted with molecular calcareous deposits that their individual 



