PACIFIC AND BEERING’S STRAIT. 
19S 
quence of the wall being broken by channels into the lagoon ; but on CHAP, 
examination, the chain is found continuous under water; and as in all 
probability it will in time reach the surface and become dry, the whole March, 
group may be considered as one island. 
In the plans which I have delivered into the Admiralty, the figure 
and extent of thirty coral islands, out of the many which exist in the 
Pacific, are carefully delineated, and a reference to them will more fully 
explain the nature of them than any description I can give here. One 
of these plans* being of particular interest, I have inserted it in the 
present work, as it exhibits, not only the coral chain enclosing the 
lagoon, which is the common character of the coral islands ; but, also, 
an example of several volcanic islands rising within it ; and likewise 
the peculiarity of the inequality in the sides of the chain mentioned in 
page 189. 
The i?Cfl5ject of the formation of these islands is one of great in- 
terest, and will require a numerous and careful collection of facts before 
any entirely satisfactory conclusion can be arrived at. I regret that 
my time did not permit me to inquire more particularly into this 
curious matter; but having to survey about fifty islands, some of 
which were of great extent, in the space of about four months, I 
Could not accomplish more than was absolutely necessary to the pur- 
poses of a safe navigation of the Archipelago. We were, however, not 
inattentive to the subject, and when opportunity offered, soundings 
Were tried for at great depths, and the descent of the islands w^as re- 
peatedly ascertained as far as the common lines would extend. Some 
cf these experiments are given in the annexed plate, representing 
a section of a coral island from actual measurement. 
In considering the subject of these coral formations, my attention 
Was drawn to the singularity of the occurrence of openings in them, 
cither opposite to, or in the direction of some stream of fresh w ater 
from the mountains ; and on searching several charts, I find so many 
corroborations of the fact, that I have no doubt of the truth of it : as 
fs-f as my own observations extended, it was always so. Ihe aversion 
* See the plan of Gambler group. 
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c c 
