1869.] RA.TTKAY CAPE-YORK PENINSULA. 303 



probably be found in the shoaling of the inner barrier-reef route and 

 the numerous openings through it, as well as the reef itself, which 

 will one day be out of water, like Eaine and other islands, when the 

 region is resurveyed many years hence. 



The great barrier-reef of Australia is evidently formed by the 

 growth of coral on the summit of a lengthy submarine hilly ridge, 

 which runs at a distance of from fifty miles, at its southern extremity, 

 midway down the east coast (lat. 22° S.), to ten miles, near Cape 

 York, leaving a long shallow vaUey between it and the mainland, 

 now converted into the navigable passage named the inner barrier- 

 reef route, the depth of which varies only from 10 to 50 fathoms ; 

 whereas the outer aspect of the reef shelves steeply like a wall, no 

 bottom being found only a short distance off at 100 to 250 fathoms, 

 where the clear and dark-green waters and long ocean-swell form a 

 marked contrast to the light green of the tranquil but turbid inner 

 passage. The reef may be said to consist of the reef proper and 

 islands. The former, which constitutes the main mass of this lengthy 

 coral tract, consists of a series, of broad flat irregular more or less 

 rounded or oval ledges of coral in full activity, covering the tops 

 of the submarine hills, occasionally dry but usually close to the 

 surface at low water, and sometimes many miles long, their position 

 at high water being marked by a line of surf or the Kght green hue 

 of the shallow water over them. On the other hand the islands 

 are of three different kinds, viz. igneous, coral islands, and sand- 

 banks. 



1st. Occasionally the higher peaks of this barrier ridge project 

 well out of the water, as in the Eorbes, Hardy, Cockburn, Murray, 

 and other islands, which are in a line with and really form part of 

 the range — and Sunday, Lizard, Eagle, the Franklands, Dunk, 

 and others, which lie between it and the coast. Round these pro- 

 jecting masses of crystalline rock we find the usual fringing reef 

 of coral, of species identical with those growing on the summits of 

 the ridge which forms the barrier proper. But on their sides we 

 find no evidence of coral growth, proving that though they must 

 have, at least, once been submerged, Hke the adjacent continent, this 

 must have been when no coral grew in the Australian seas. 



2nd. Here and there, however, we meet with islands of another 

 class, of which Raine, Cairncross, the Howick group, &c. may be 

 taken as types, a few of which, like the fii'st named, form part of 

 the reef, but the majority, like the last of the three, are met with in 

 clusters, between it and the mainland. Raine island, taken as an ex- 

 ample, which possesses its own special and active fringing reef, is low, 

 flat, about one-third of a mile long and a quarter of a nule broad ; it 

 rises about 10 feet above high water, and consists of hard compact brec- 

 ciated coral conglomerate, with a shelving beach of coarse coralline and 

 sheUy sand, and a scanty superstratum composed of the coral debris 

 sparingly mixed with vegetable matter, and a thin layer of guano de- 

 posited by the numerous turtle and flocks of terns, gannets, and other 

 aquatic birds that, like the former, make this their headquarters 

 and favourite breeding-place. The whole constitutes a soil capable 



