142 CORAL FORMATIONS. 
one of them, near New Britain, and another (Vulcano) near longitude 
145° E., are in action. 
From the facts thus far detailed, the connexion between the pre- 
valence or extent of reefs, and the various causes assigned as limiting 
or promoting their growth, is obvious. The amount of subsidence 
determines in some cases the distance of barrier reefs from shores; 
but it by no means accounts for the difference in their extent in dif- 
ferent parts of a single group of islands. Indeed, if this cause be 
considered alone, every grade of extent, from no subsidence to the 
largest amount, might in many instances be proved as having occurred 
on asingle island. Of far greater importance, as has appeared, is the 
volcanic character of the land. At whatever time the existing reefs 
in the Pacific commenced their growth, they began about those of 
the igneous islands whose fires had become nearly or quite extinct ; 
and as others in succession were extinguished, these became in their 
turn the sites of corals, and reefs began to form. Those lands whose 
volcanoes still burn, are yet without corals, or there are only limited 
patches on some favoured spots. Zoophytes and volcanoes are the 
land-making agents of the Pacific. The latter prepare the way by 
pouring forth the liquid rock, and building up the lofty summit. Quiet 
succeeds, and then commences the work of the zoophyte beneath the 
sea, while verdure covers the exposed heights. 
We may add a few more illustrations from other parts of the coral- 
reef seas. 
Along the north and northwest coast of New Holland, there appears 
to be little or no coral in the Gulf of Carpentaria, while some exten- 
sive patches occur on the shores west of this gulf, as far as the north- 
west cape in latitude 23° S. 
In the East Indies, there are large, scattered reef-islands, south of 
Borneo and Celebes, and the west end of New Guinea. The islands 
of ‘Timor-laut, and Timor, with many of those intermediate, have 
large reefs. The Arru Group consists wholly of coral. This sea, 
from Arru to the islands south of Borneo, is more thriving in corals 
than any other in the East Indies. 
Another Hast India coral reef region, of some extent, is the Sooloo 
Sea, between Mindanao and the north of Borneo. Yet the reefs 
are mostly submerged. We saw no wide platforms bordering the 
high lands, like those of the Pacific. ‘There are, however, some 
small coral islets in the Balabac Passage. 
In other parts of the East Indies, coral reefs are quite inconsider- 
