as indicated by the Distribution of Coral Islands. 133 
On examining a map of the Pacific, between the Sandwich 
Islands and the Society group, we find a large area just north of 
the equator with scarcely an island. 'T’o the south, the islands 
increase in number, and off Tahiti, to the northward and east- 
ward, they become so numerous, and are so crowded together, as 
to form a true archipelago. They are all, too, coral islands, 
throughout this interval. This then is a rather remarkable fact 
in the distribution of these islands. But let us look farther. 
If we draw a line running nearly E. 8. E. from New Treland, 
near New Guinea, just by Rotumah, Wallis’s Island, Samoa or 
the Navigators, the Society Islands, and thence bending south- 
ward a little, to the Gambier group, (see map,) we shall have all 
the islands to the north of it, with two or three exceptions, purely 
coral, while those to the south, are very generally, high basaltic 
islands. ‘These basaltic islands are bordered by reefs, and these 
reefs are most extensive about the islands nearest this line. In 
the Feejees, the northeastern part of the group contains some 
coral rings, while the southwestern consists of large basaltic isl- 
ands with barrier reefs. 
Again, to the north of this boundary line, the islands farthest 
from it, are usually small, in many instances mere points of reef, 
a fraction of a mile in diameter, while some of the coral islands 
near the same line are thirty or forty miles in length. 
Now a growing coral island or atoll, will gradually become 
smaller in diameter as subsidence goes on, and by the same pro- 
cess must finally be reduced to a mere spot of reef, or, if the sub- 
sidence is too rapid, that is, more rapid than the growth of the 
coral, the island will become wholly submerged and leave noth- 
ing at the surface. 
On these principles, I base my conclusions. Along the equa- 
tor, as explained, there is a large area containing few islands, and 
these small, while farther south, the coral islands are numerous 
and large: Is this not evidence, that the subsidence was either 
more rapid or carried on for a longer period in the former region 
than in the latter, where they are numerous and large? 
Near the boundary line pointed out, stand some of these coral 
rings enclosing mountain tops, as islets,—as at the Gambier group. 
Does not this indicate that the subsidence was less here than 
among the islands purely coral to the north? and greater, than 
south of the line, where the reefs are more contracted and the 
high islands larger and more elevated ? 
