50 THE GREAT BARRIER REEF. 



black and weathered; and, standing up in bold colour, are in contrast with the snow-white line of 

 breakers. They are popularly known as "nigger heads." Jukes, in his "Voyage of the Fly,' 

 attests to examples of analogous blocks resting on the Barrier margin, twelve miles south-west of 

 Raine's Islet. They are situated about two hundred yards from the outer edge of the reef, and 

 measure, in some instances, no less than from twenty to twenty-five feet long and ten or twelve 

 feet high ; their summits are, in some cases, elevated as much as eight feet above high-water. 

 The general surface of these rocks is very rugged and honeycombed, and passes upwards 

 in sharp points and crags, and it was only in the sheltered hollows one could detect that 

 they were composed almost entirely of a species of Porites, with the cells for the most 

 part directed upwards in apparently their natural position of growth. Commenting on these 

 huge dimensions, Mr. Jukes was doubtful whether or not to regard the blocks as remnants of 

 a much larger mass that had been gradually eaten away and eroded by the action of sea 

 and weather, and as furnishing evidence of elevation in this region. The fact that these 

 huge blocks seemingly passed down into the main body of the reef lent support to this 

 suggestion. This embedment in, or solid union with, the main body of the roof is, however, 

 characteristic of all similar stranded masses of any antiquity, and is of itself corroborative 

 evidence of the augmentation of the reef conglomerate that is constantly, though slowly, 

 progressing within intra-tidal areas. To go further, it will be hereafter shown that the deep 

 embedment of those cast-up rock-masses in the substance of the reef is direct evidence of 

 subsidence rather than of elevation. 



Mr. Jukes' doubts as to the possibility of the masses he described being lifted to their 

 position on the reef by any conceivable storm may be set aside in face of the ocular evidence, 

 in both this and the succeeding plate, of what can be effected by storm-waves in confined 

 channels and relatively shallow water. On the outer face of the Barrier, with the whole mass 

 of the fathomless Pacific to draw upon, the hydraulic lifting power of the gigantic storm- 

 begotten rollers, while practically incalculable, is sufficient to account for the transport of the 

 rock-masses above described. 



PLATE XXXI. 



HURRICSNE-STRINDED CORAL-MISSES, PORT DENISON, 



A still more graphic exposition of the role enacted by cataclysmic influences in the making 

 and unmaking of coral-reefs, and the associated products, is furnished by the accompanying 

 plate. It represents the north-west shore of Saddleback Island, Port Denison, which has already 

 furnished the subjects of several illustrations. The coral-masses piled up here in inextricable 

 confusion represent the complete wreckage, by a hurricane, of the fringing reef that skirted 

 this side of the island. The massive Astraeaceae, Meandrina', and Symphyllias have been 



