346 CORALS AND CORAL ISLANDS. 
The amount of subsidence determines in some cases the dis. 
tance of barrier reefs from shore ; but it by no means accounts 
for the difference in their extent in different parts of a single 
croup 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 a 
single island. Of far greater importance, as has appeared, is 
the voleanic character of the land. At whatever time the ex- 
isting reefs in the Pacific commenced their growth, they be- 
gan about those of the igneous islands whose fires had become 
nearly or quite extinct; and as others in succession were ex: 
tinguished, these became in their turn, the sites of corals, and 
of coral reefs. Those lands whose volcanoes still burn, are 
yet without corals, or there are only limited patches on some 
favored spots. Zodphytes and volcanoes are the land-making 
agents of the Pacific... The latter prepare the way by pour 
ing forth the liquid rock, and building up the lofty summit. 
vu ‘Quiet succeeds, and then commences the work of the zoophyte 
beneath the sea, while verdure covers the exposed heights. © 
“ia _ ¥%& We may add a few more illustrations from other parts of 
the coral-reef seas. 
Along the north and northwest coast of Australia, there 
appears to be little or no coral in the Gulf of Carpentaria, 
while some extensive patches occur on the shores west of this 
Gulf, as far as the northwest cape in latitude 23° S. 
In the East Indies, there are large, scattered reef-islands 
south of Borneo and Celebes, about some of the Molluccas, 
and near the west end of New Guinea. The islands of Timor- 
laut, and Timor, with many of those intermediate, have large 
rects. The Arru Grou» consists wholly of coral. This sea, 
from Arru, to the islands south of Borneo, is more thriving in 
corals than any other in the Kast Indies. 
