THE ATOLL AS A WHOLE 139 



flat. The essential feature which constitutes the varying factor, 

 in the parts of the ring which are not the sites of islands, is the 

 presence or absence of the barrier ; for the barrier, which is 

 the mainstay of the existence of the atoll, must always be 

 regarded as potential dry land, although still belonging to the 

 ocean. The barrier does not form a complete rim to the reef, 

 but, as a pioneer, it outruns the land, and is wanting in only 

 about three and a half miles of the whole circumference. 

 The parts in which the barrier fails are situated to the north 

 and west of the atoll ring, and the sailors' rule, that the 

 entrance to a lagoon is to be found on the leeward side, is 

 therefore j ustified. 



The whole atoll is in the form of an ellipse with its long 

 axis stretching in a south-easterly direction — prolonged in 

 fact in the line of the prevalent wind, a common and neglected 

 feature of atoll form. The ellipse is some ten miles long from 

 barrier to barrier, and some seven miles across its short axis. 

 The whole atoll therefore occupies very much the same area 

 as does Christmas Island, its nearest neighbour. 



The largest islands lie to the south of the ring, and Pulu 

 Atas and Pulu Panjang are the largest land masses of the 

 group. Not only are they longer than any others, but they are 

 also much wider from sea beach to lagoon shore, they are the 

 highest land in the whole atoll, and are evidently the oldest of 

 any of the islands. The islands to the north are smaller, and, 

 as a rule, very much lower ; and they have evidently altered 

 very little from their primitive condition of being mere heaps 

 of coral debris. Pulu Tikus is one of the lowest of all the 

 islands in the group, and its general elevation is only from two 

 to three feet above mean tide -level ; its highest point is raised 

 some thirteen feet above the sea, and much of its surface 

 is below the level of spring high tides. It is difficult to realise 

 the extreme lowness of the islands of the atoll, and it is always 

 a cause of surprise to any one who sees these things for the 

 first time, although the fact may be perfectly familiar. As a 

 homely illustration of the actual condition, it is useful to take 

 the level of a railway line, to represent the sea, and then the 



