136 CORAL FORMATIONS. 
No less striking are the effects of volcanic action in preventing the 
formation of reefs; and instances of this influence are numerous 
throughout the Pacific. The existence of narrow reefs, or their entire 
absence, may often be thus accounted for. For example, in the Sand- 
wich Group, the island Hawaii, still active with volcanic fires, has 
but few traces of corals about it, while the westernmost islands, which 
have been longest free from such action, have reefs of considerable 
extent. The island of Maui exemplifies well the general fact. The 
island consists of two peninsulas: one, the eastern, recent volcanic, with 
a large crater at summit, and the other, the western, presenting every 
evidence in its gorges and peaksand absence of volcanic cones, of having 
become extinct ages since. In conformity with the view expressed, 
the coral reefs are confined almost exclusively to the latter peninsula. 
Other examples are afforded by the Samoan Islands. Savaii abounds 
in extinct craters and lava streams, and much resembles Hawaii in 
character; it bears proof in every part of being the last seat of the 
volcanic fires of Samoa. Its reefs are consequently few and small: 
there is but a narrow line on part of the northern shores, although on 
the other islands they are very extensive. ‘The absence of corals 
results obviously from the destruction of zoophytes by heat, consequent 
on voleanic action. Submarine eruptions, which are frequent as long 
as a volcano near the sea is in action, heat the waters, and destroy 
whatever of life they may contain. After the eruption of Kilauea, in 
1840, there were numerous dead fish thrown on the beach; and many 
such instances in different regions are on record. Other facts, illus- 
trating the effects of volcanic heat in preventing the growth of reefs, 
will be brought forward in the following pages. 
The agencies affecting the growth of coral reefs being before the 
mind, we may proceed to notice the actual distribution of reefs through 
the coral seas. ‘The review given is a rapid one, as our present ob- 
ject 1s simply to explain the absence or presence of reefs within the 
coral-reef limits, by reference to the above facts.* 
* In the valuable work by Mr. Darwin, the geographical distribution of reefs is treated 
of at length in the Appendix, pp. 151-205. ‘The facts here detailed have been obtained 
from independent sources, except where otherwise acknowledged. In accounting for the 
character and distribution of reefs, Mr, Darwin has erred in attributing too much weight 
to a supposed difference in the amount of subsidence in different regions, neglecting to 
allow the requisite limiting influence to volcanic agency, and to the other causes men- 
tioned, 
