186 CORAL AND ATOLLS 



larger scale, and a line of transition from coral shoal to sand- 

 silted lake is sweeping, as a crescent, from south to north. 



The entrance to the lagoon is situated to the north of 

 the atoll, and here the bottom of the lagoon merges with the 

 comparatively shallow areas of the" coral ridge, and is seen in 

 its most luxuriant growth, and in its most primitive condition. 

 Between Pulu Luar and Pulu Tikus the barrier is entirely 

 wanting, and in this gap the original coral bed lies at a few 

 fathoms' depth with its luxuriant mixed growth of massive 

 corals undisturbed by violent wave action. This coral bed 

 is, no doubt, the type of the original condition of the whole 

 area of the ridge now occupied by the southern atoll and the 

 northern atollon of Keeling Island, 



The shallow southern part of the lagoon extends in the 

 form of a great horse-shoe, skirting the inner shores of the 

 islands, and invading at its margins the northern deeper part. 

 Its area may be roughly taken as slightly more than half the 

 total lagoon area, or about thirteen square miles. Large areas 

 of its most southern parts are dry at low water, and covered by 

 a few feet of water only at full high tide. The more northerly 

 and central parts of the shallows are covered by anything less 

 than a fathom of water at low tide. The bottom of this part 

 is, however, not at all uniform, and deeper hollows are studded 

 about the central portions of the greater part of the southern 

 shallows. 



Along the inner shores of the large islands, Pulu Atas and 

 Pulu Panjang, the long sand flats are dry for a mile or so at 

 low tide, and at full high tide a great part of this flat has no 

 more than an inch or two of water on it. Towards the shore, 

 these flats become continuous with the oozy white mud which 

 collects in the lagoonlets of these two islands, and towards the 

 lagoon they slope gradually to the slowly deepening water, 

 which is clearly indicated as a bright green belt, merging after- 

 wards to the characteristic deep blue. 



Bushes of Pemphis acidula and pioneer coconut palms 

 stand here and there as outposts of the land : and it is the 

 policy of the islands that these pioneers are not interfered 



