238 THE INFLUENCE OF INANIMATE SURHOUNDINGS. 



with fragments of shells and corals; these strata are intersected 

 by others lying at from 1 to 1*5 foot lower, which are quite 

 free from detritus, and are formed of blocks of coral so perfectly 

 baked together that in many places they appear to form a 

 homogeneous and compact coralline limestone. Such strata of 

 metamorphosed coralline limestone also occur, but much more 

 rarely, on the summits or inner sides of the islands further to 

 the south. The greater part of this eastern reef is covered by 

 the sea only at high tide ; then its surface lies at from 1 to 2 

 feet below water. Above this the raised margin of the islands 

 stands up from 5 to 6 feet. Its outer slope is steep, and the 

 summit is crowned by blocks of coral of no conspicuous size, 

 which have evidently been carried up during violent storms. 

 The eastern slope of the reef to the sea is not steep, as can 

 be seen by the colour of the water ; in the south-west monsoons 

 good anchorage is found here at some distance from the reef. 



The reef to the west is devoid of islands, and its structure 

 differs essentially from that of the eastern reef. While this is 

 laid quite dry at every ebb tide , the former cannot be crossed 

 dry-foot excepting at spring-tide ebbs. It follows from this 

 that the western reef must lie from 4 to 5 feet lower than the 

 eastern one ; for in so small an island, bathed all round by the 

 same ocean, it is impossible to suppose that this difference can 

 be caused solely by the water being dammed up on the 

 eastern side. 



This western reef rises with a not very steep slope from 

 the lagoon ; it is . moderately broad, almost level, and at 

 first only covered by coralline sand very equally distributed ; 

 towards the north and south points of the atoll it rises 

 more than on the west. Nearer to the outer margin of the 

 reef occur living but isolated blocks of coral, at first in 

 small masses and few in number, but the further we go west- 

 ward the larger and more frequent they become, till at length 

 all sand has disappeared and the blocks of coral are no longer 

 isolated, but a solid, connected mass. Here we rarely meet 

 with dead blocks among the living coral. Of course the coral 

 grows most vigorously outside the external reef. The slope of 

 this western reef, unlike the eastern one, is very abrupt ; at a 



