THE LAGOON 197 



Madrcpora pulchra which are causing the alteration. These 

 beds are bringing about a somewhat rapid shoaling of the 

 lagoon in this spot, for M. pidcJira is a type of colony well 

 formed to resist some degree of sedimentation ; and not only 

 are the colonies growing very actively, but are holding in their 

 dead lower branches a great amount of drift sand. They are 

 therefore forming banks, with living branches actively growing 

 at the summit, and sand, held fast among the dead branches, 

 at the base. Another type of colony thriving in this environ- 

 ment is a plate growth of Montijjora, approximating to the type 

 named M. circinata ; it plays very much the same part as 

 Echinopora lamdlosa does in the southern shallows, and grows 

 upon the sides of the banks, holding the sand back behind its 

 broad leaves. 



Although the water is, in many places, six or eight fathoms 

 deep over wide stretches in the northern part of the lagoon, 

 the nature of the coral colonies that lie below can nearly always 

 be made out, and where the lagoon falls to the open sea, 

 between Pulu Tikus and Pulu Luar, the parti-coloured bottom 

 may be seen for a very great distance. The fall from the 

 shallow waters of the lagoon to the ocean outside is not nearly 

 so abrupt as has been imagined, for the entrance, lying to the 

 north, corresponds with the northward tailing out of the bank 

 on which the atoll is formed — the bank upon whose northern 

 extremity Keeling atollon is situated. When sailing from the 

 lagoon, the bottom is seen as a patchy background through 

 water that becomes increasingly blue ; at first yellow masses 

 of Porites alternate with white patches of sand, and blue 

 patches of the deeper holes ; then the patches blend more, and 

 lighter yellow areas and darker blue areas alone are seen. 

 When still farther from the atoll only the larger patches show 

 at all, and the appearance is somewhat that seen when looking 

 from a hillside upon distant fields, differently coloured by 

 various growing crops. Alternations in colour are seen for 

 long ; and the whole picture, from minute detail to complete 

 blurring, fades slowly. I can speak of this point with some 

 certainty, for I have many times been in and out of the lagoon, 



