890 Proceedings of the Royal Society 
will, however, have been gathered from the previous remarks that 
local conditions will usually confine reef-corals to depths less than 
25 or 30 fathoms, and that it will be only under occasional circum- 
stances that reefs will commence to be formed in deeper water. 
Fringing-reefs themselves are at first restricted to shallow waters 
around the coast, and their seaward extension in localities where 
the submarine slope is at all steep, as is generally the case, must be 
extremely slow T . Again, in a area of elevation, such as that in 
which the Solomon Islands are included, barrier-reefs, which may 
have begun to grow in depths not less than 50 fathoms, might owe 
their approach, towards the surface as much to the elevating move- 
ment as to the very slow upward growth of the corals. It should 
also be borne in mind that the rapid subserial denudation, to which 
these regions of heavy rainfall are subjected, would be an important 
agency in the thinning away of the raised coral formations. 
The Evidence of the Outward Growth of Barrier-Reefs and 
Atolls . — * (a) Whilst examining Oima Atoll, I was particularly 
struck with the difference in size between the massive corals 
in the interior of the lagoon and those which occurred near or 
at the outer border of the reef. In the lagoon, the large masses 
of Porites ranged from 10 to 16 feet in diameter; whilst the 
largest masses that I found in the wash of the breakers at 
the outer edge of the reef, which belonged to species of Cceloria 
and Meandrina, measured only 5 feet across. I have also noticed, 
in the case of barrier-reefs in this strait, that the massive corals are 
largest near the inner edge of the flat and diminish in size as one 
approaches the outer edge of the reef. Thus, in case of one of the 
Shortland reefs, I found masses of Porites at the inner edge of the 
flat which measured from 6 to 1 0 feet across ; whilst the largest 
massive corals (referable to the genera, Coeloria and Meandrina), 
that I found near the outer edge of the reef, measured from 3 to 4 
feet. These facts are of importance, since, according to the theory 
of subsidence, the central portion of the lagoon of an atoll and the 
inner portion of the lagoon-channel of a barrier-reef are more 
recently produced than any other portion of the area of such reefs. 
Here, then, the massive corals ought to be much smaller than those 
* This mode of growth is one of the chief points on which Mr Murray dwells. 
My observations go to support his view. 
