54 THE GREAT BARRIER REEF. 



been reproduced here, viz., a view of the low sand cliff immediately facing the beach on 

 Sweer's Island, where the specimens just described were collected. As since ascertained, it 

 was the subject of observation by Captain King, and is referred to in Vol. II. of his "Surveying 

 Voyage to Australia." The composition of the cliff is described by Captain King as "a stalactite 

 concretion of quartzose, sand, and fine gravel, cemented by reddish carbonate of lime." The 

 aspect of this cliff is very singular, its exposed face being, as it were, evenly fluted, and 

 composed of closely-aggregated sand tubuli, which are continued perpendicularly through the 

 substance of the cliff, such structure giving detached portions of the mass, when viewed 

 vertically, a coarsely-honeycombed appearance. Some twenty years ago Sweer's Island was 

 visited by a devastating hurricane, which well nigh wrecked the homestead established there, 

 and during it this cliff, ranging from ten to twenty feet in height, was more or less completely 

 submerged. Similar invasions of the sea have, no doubt, occurred at irregular intervals throughout 

 many centuries. These cataclysmic inundations, supplemented by the showers of spray thrown 

 abundantly on the face and shore borders of the cliff by ordinary storms, amply account, 

 taking into consideration the lime-saturated and cementing properties of the sea-water, here 

 attested to, for this remarkable aggregation of lime and silica. The action of the latest hurri- 

 cane, and accompanying inundation, it may be here mentioned, was to undermine an extensive 

 area of the face of the cliff, to such an extent, that a large portion has fallen down and lies 

 scattered in huge, heaped-up blocks at high-tide level. A little way inland, out of the reach 

 of the sea and spray, the stratum of siliceous sand and ironstone gravel occurs without any 

 admixture of carbonate of lime. 



PLATEXXXIII. 



(]1,)-0UTER BIRRIER REEF, WITH SUBMERGED BECHE-DE-MER, 



This reef-scene is taken from an area closely abutting upon the one (Plate XXIX.) illustrating 

 the natural habitat of the Giant Clam-shell, Tridacna gigcis. The specimens of Beche-de-mer, 

 dimly visible through the water in the foreground, towards the left, are what are known as 

 "ordinary Red-fish," Adinopyga obesa, one of the most valuable commercial species. The several 

 small fishing vessels discernible on the distant horizon represent the description of shallow- 

 draught craft most commonly employed in this fishery, and manned with native crews, by wliom 

 a clean sweep will presently be made of the many thousands of Beche-de-mer, similar to those in 

 the foreground, scattered over the vast surface of the reef. There is a conspicuous coral-growth 

 in this reef-view that does not enter into the composition of the preceding plates. This is 

 represented by the obtusely-lobed, or clavate, masses nearest to the front on the left-hand 

 side, and by an isolated corallum in the lower right-hand corner. This species, Alveopora retiisa, 

 is remarkable for the extremely porous, almost lace-like, delicacy of its superficial corallites. 



