in the Pacific, ^c. 141 



water, and so bold that one may spring upon it from a boat 

 without wetting his feet. So trifling is the depth of water 

 on other reefs, that many arborescent and some even of the 

 sessile corals, have their superior portions so constantly expos- 

 ed that the polypes are all dead, while below a certain line 

 they still continue to flourish. In the lagoons, also, are fre- 

 quently seen clusters of Madrepore, whose extremities are 

 from an inch to a foot above water, which like those on the 

 terraces could have been constructed by the polypes, only 

 when continually covered by it. 



At Christmas Island, the re-elevation has been so great, that 

 the lagoon, of sixty miles in circuit, is in no part, at half a mile 

 from shore, more than three feet deep, has hardly any where 

 over ten feet of water at high tide and is full of stfll shal- 

 lower patches, raised reef-rock, and corals. On the south-east 

 side, numerous lagoons from a quarter of a mile to a couple of 

 leagues in compass, originally no doubt deep hollows in the 

 principal one, have been formed by the elevation of their sur- 

 rounding bed above water. In some of these, though they 

 have no outlet, the tide continues to rise and fall regularly, 

 the water passing readily through the porous sand, but the 

 evaporation is such as to render them exceedingly salt. In 

 others, the water is entirely dried up, and the bottom covered 

 with a thick saline incrustation. The intervals between these 

 small lagoons and hollows, is sometimes the bare coral rock, 

 but more commonly coral sand and shells, containing an infi- 

 nite number of Echini, Spatangi, 6cc. imbedded. Near the 

 centre of the island are plains of perfectly level coral rock, 

 some of them a mile long by half a mile broad, raised eight 

 or ten feet above sea level, and covered with about a foot of 

 black porous earth. The magnitude of these rocks precludes 

 all idea of their having been torn from the reef like the large 

 blocks of similar composition that line the eastern coast. A 

 very remarkable character in the structure of this island is 

 the unusually great width of the two entrances, it being full 

 two miles, as will be seen by the accompanying sketch. The 

 fringing reef runs out about half a cable's length all round 

 the island, except on the south-west side, where the surf rolls 



