ibb 
DISTRIBUTION OF CORAL-REEFS. Ch. VI. 
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 1 has described an atoll-formed 
reef in lat. 10°, seven miles long and from one to three 
broad, resembling a boot in shape, and apparently in- 
cluding a deep lagoon. 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 barrier-reefs of Australia and 
New Caledonia, there are many low islets and coral- 
reefs, some of which are annular, cr like a horse-shoe. 
Bearing in mind the smallness of the scale of our map 
(the lines of latitude being 900 miles apart), we see that 
none of the larger groups of reefs and islands which are 
coloured blue, and which are supposed to have been 
produced by long-continued subsidence, lie near exten- 
sive lines of coast coloured red ; these latter having 
either long remained stationary, or having been upraised 
with new reefs re-formed on them. Where 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 ; and elevation having preceded the subsidence 
of the blue spots ; and in this case the juxtaposition of 
reefs belonging to the two great types of structure is 
little surprising. We find, therefore, that atolls and 
barrier-reefs, which both owe their origin to subsidence, 
lie near together and are as a general rule separated 
' Voyage to Terra Australis, vol. ii. p. 336. 
