158 CORAL-REEFS. 



of encircled islands is that of the Society Archipelago ; and 

 these islands are surrounded by atolls, and only separated 

 by a narrow space from the large group of Low atolls. 

 In the midst of the Caroline atolls, there are three fine 

 encircled islands. The northern point of the barrier-reef of 

 New Caledonia seems itself, as before remarked, to form a 

 complete large atoll. The great Australian barrier is de- 

 scribed as including both atolls and small encircled islands. 

 Capt. King 1 mentions many atoll-formed and encircling 

 coral-reefs, some of which lie within the barrier, and others 

 may be said (for instance between lat. 16 and 13 ) to form 

 part of it. Flinders 2 has described an atoll-formed reef in 

 lat. io°, seven miles long and from one to three broad, 

 resembling a boot in shape, with apparently very deep water 

 within. Eight miles westward of this, and forming part of 

 the barrier, lie the Murray Islands, which are high and are 

 encircled. In the Corallian Sea, between the two great 

 barriers of Australia and New Caledonia, there are many 

 low islets and coral-reefs, some of which are annular, or 

 horse-shoe shaped. Observing the smallness of the scale 

 of the map, the parallels of latitude being 900 miles apart, 

 we see that none of the large groups of reefs and islands 

 supposed to have been produced by long-continued sub- 

 sidence, lie near extensive lines of coast coloured red, 

 which are supposed to have remained stationary since the 

 growth of their reefs, or to "have been upraised and new 

 lines of reefs formed on them. Where the red and blue 

 circles do occur near each other, I am able, in several 

 instances, to show that there have been oscillations of level, 

 subsidence having preceded the elevation of the red spots ; 



1 Sailing Directions, appended to vol. ii. of his Surveying Voyage to 

 Australia. 



2 Voyage to Terra Australis, vol. ii. p. 336. 



