62 CORAL FORMATIONS. 
the direction of the cells that they did not stand as they grew; on 
the contrary, they had been upthrown and were afterwards cemented 
with the material of the rock beneath them, probably at the time this 
rock itself was consolidated. Below some of the loose masses like 
figure 3, (as on Aratica,) the platform was at times six inches higher 
than on either side of the mass, owing to the protection from wear 
given to the surface beneath it. ‘These blocks are always extremely 
rough and uneven, like those of the emerging land beyond; and the 
angular features are partly owing in both cases to solution from rains 
or from the sea-water that may be dashed over them. 
It should be distinctly understood that these masses here described 
were found isolated, and only at considerable intervals. In no instance 
were they observed clustered. ‘The loose blocks and those cemented 
below bad the same general character, and must have been placed 
where they were by the same cause, though it may have been at 
different periods. 
The shore of the lagoon is generally low and gently inclined, yet in 
the larger islands, in which the waters of the lagoon are much dis- 
turbed by the winds, there is usually a beach resembling that on the 
seaward side, though of less extent. A platform of reef-rock at the same 
elevation as the shore platform sometimes extends out into the lagoon ; 
but it 1s more common to find it a little submerged and covered for 
the most part with growing corals: and in either case, the bank ter- 
minates outward in an abrupt descent of a few yards or fathoms, to a 
lower area of growing corals, or a bottom of sand. Still more com- 
monly, we meet with a sandy bottom gradually deepening from the 
shores without growing coral. These three varieties of condition are 
generally found in the same lagoon, characterizing its different parts. 
The lower area of growing corals slopes outward, and usually ceases 
where the depth is 10 to 12 fathoms; from this there is another descent 
to the depth which prevails over the lagoon. 
On some small lagoons the shore is a thick plastic mud, either 
white or like clay, and forms a low flat which is very gently sloping. 
On Henuake, these mud deposits are quite extensive, and of a white 
colour. At Enderby’s Island, another having a shallow lagoon, the 
mud was so deep and th.ck that there was some difficulty in reaching 
the waters of the lagoon; the foot sunk in 8 or 10 inches and was not 
extricated without some difficulty. The colour at this island was 
a dirty brownish clay. This mud is nothing but comminuted coral, 
so fine as to be almost impalpable. 
