Sect. I. KEELING ATOLL. 9 



which forms great irregularly rounded masses (like 

 those of an Astrsea, but larger) from four to eight feet 

 broad, and little less in thickness. These mounds are 

 separated from each other by narrow crooked channels, 

 about six feet deep, most of which intersect the line of 

 reef at right angles. On the furthest mound, which I 

 was able to reach by the aid of a leaping-pole, and over 

 which the sea broke with some violence, although the 

 day was quite calm and the tide low, the polypifers in 

 the uppermost cells were all dead, but between three 

 and four inches lower down on its side they were living, 

 and formed a projecting border round the upper and 

 dead surface. . The coral being thus checked in its up- 

 ward growth, extends laterally, and hence most of the 

 masses, especially those a little further inwards, had 

 broad flat dead summits. On the other hand I could 

 see, during the recoil of the breakers, that a few yards 

 further seaward, the whole convex surface of the Porites 

 was alive : so that the point where we were standing 

 was almost on the exact upward and shoreward limit of 

 existence of those corals which form the outer margin 

 of the reef. We shall presently see that there are other 

 organic productions, fitted to bear a somewhat longer 

 exposure to the air and sun. 



Next, but much inferior in importance to the 

 Porites, is the MilLepora complanata. 1 It grows in 

 thick vertical plates, intersecting each other at various 



1 This Millepora, (Palmipora of Blainville,) as well as the M. aki- 

 cornis, possesses the singular property of stinging the skin where it is 

 delicate, as on the face and arm. 



