PACIFIC AND BEERING’S STRAIT. 
187 
formed of coral, except Henderson’s Island, which was partly sur- CHAP, 
rounded by it ; and they all appeared to be increasing their dimensions 
by the active operations of the lithophytes, M^hich appeared to be gra- ^Feb. 
dually extending and bringing the immersed parts of their structure to 
the surface. 
Twenty-nine of the number had lagoons in their centres, which is 
a proportion sufficiently large, when coupled with information sup- 
plied from other parts of the globe where such formations abound, 
to render it almost certain that the remainder also had them in the 
early period of their formation, and that such is the peculiar structure 
of the coral islands. And, indeed, these exceptions can scarcely be consi- 
dered objections, as two of them — Thrum Cap, which is only seventeen 
hundred yards long by twelve hundred broad ; and Queen Charlotte’s 
Island, which is not more than three quarters of a mile wide in its 
broadest part, and less than half a mile in other places— are so circum- 
stanced, that, had their lagoons existed, they would have been filled in 
the course of time with the masses of coral and other substances which 
the sea heaps upon such formations as they rise above the surface : they 
have, besides, long been wooded and inhabited, though deserted at the 
present moment, both of which would tend to efface the remains of a 
lagoon of such small dimensions. The sea, however, prevented our 
boats from landing upon either of these islands to ascertain the fact 
of the early existence of lagoons. The other exception, Henderson s 
Island, though of coral formation, appears to have been raised to its 
present height above the sea by a subterraneous convulsion, and has its 
centre so incumbered and overgrown with bushes that we could not 
determine whether it ever had a lagoon. 
In the above-mentioned twenty-nine islands the strips of dry coral 
enclosing the lagoons, divested of any loose sandy materials heaped 
Upon them, are rarely elevated more than two feet above the level of 
the sea ; and were it not for the abrupt descent of the external margin, 
which causes the sea to break upon it, these strips would be w'holly 
inundated : this height of two feet is continued over a small portion only 
of the width of the island, which slopes on both sides, by an almost 
iniperceptible inclination to the first ledge, where, as I said before, its 
B B 2 
