TRUK. . 359 



been partly killed and covered with Nullipores the belt forms the extension 

 of the shore line. In somewhat deeper water, the corals form huge clumps 

 separated by lanes of sand ; the corals do not reach a greater depth than 

 five to eight fathoms, when they disappear, having gradually become sepa- 

 rated by wider and wider lanes of coralline sand as they extend into deeper 

 water. In depths of less than seven to eight fathoms, huge patches of 

 black coralline Algaj, alternating with large masses of Millepores and 

 Madrepores, are found scattered over the bottom of the fringing reef belt. 

 Large pieces of coral rock have been thrown up on the beach ; they are 

 derived from adjoining elevated masses of undercut coral beach rock ; 

 this would indicate near the landing of Uola an elevation of some three 

 to four feet. The fringing reef impinges on a steep sand beach about five 

 feet in height, and in some parts has formed a flat of at least 1000 feet in 

 width, over which large coral boulders are scattered. This flat has been 

 formed on the top of the extension of the adjoining volcanic slope or flat, 

 and abuts against the volcanic sides of the hill. The honeycombed and 

 weathered coral masses, occurring as outliers on the volcanic slopes, indicate 

 the height to which this flat must once have been elevated. 



When volcanic outbursts have thrown up limestone masses, the action of 

 solution, disintegration, denudation, and erosion upon such rocks is very 

 rapid ; sea-water also carries off in solution and suspension a large amount 

 of material, leaving fewer spits and outliers than is the case when volcanic 

 rocks are subject to the same agencies. 



On this limestone plateau cocoanut trees are growing in great profusion. 

 On the volcanic hillsides the vegetation consists of breadfruit trees, sago 

 and ivory nut palms and Pouka trees (PI. 192, fig. 2). Tlie shore of Uola 

 is flanked by a narrow fringe of mangroves, growing close to the sand 

 beaches, or of mangrove islets formed mainly of volcanic sand mixed with 

 coral sand (PI. 192, fig. 1). Off Uola the water of the lagoon is exceed- 

 ingly muddy ; a mass of volcanic silt being carried out as far as our 

 anchorage, fully half a mile from shore. 



On the south side of Uola the same conditions exist ; points of sand make 

 out from the fringing reef, and masses of corals are thrown up on the beach ; 

 reaches or patches of. black as well as green coralline AlgiB occur on the 



