OF THE TONGA ISLANDS. 599 



take their ori<i:iu in tlio lii<2;hest part of tlio island, arifl here the 

 volcanic basis is lari^ely ex})ose(l. A wide terrjice of limestone 

 Btandiiiji: at a level of 25U to 350 feet extends along the whole of 

 the western side of the island, spreading out from the lower slopes 

 of the central ridge. This will be referred to as terrace a. It is 

 \videst opposite the middle of the island, becoming narrower to north 

 and south, and forms nearly half the total area of Eua. From 

 its western border the land slopes more or less steeply to the sea. 



The western aspect of the island offers a marked contrast to the 

 eastern. Instead of the dense wind-swept forest, there are wide 

 open stretches of grass-covered country, intersected here and there 

 with belts of luxuriant })ush. The streams which have scored the 

 western slopes of the central ridge dip underground on reaching the 

 limestone terraces and pursue a subterranean course to the sea. 

 There are, however, continuing some of the stream channels, deep 

 gorges cut in the western terrace, whose sides descend abruptly from 

 the gene'ral level ; these are overflow channels, in which water runs 

 only after heavy rains. 



There is one stream, possibly there are others, in the higher part 

 of the island, which pursues a different course. At an elevation of 

 about G20 feet there is a funnel-shaped depression in the volcanic 

 deposits ; and at the bottom of this funnel a vertical shaft descends 

 several hundred feet into the interior of the island. Its mouth 

 measures about 100 feet in one diameter and 30 feet in the other. 

 After flowing down the side of the depression the stream falls into 

 the shaft, pouring over the layers of hardened tuff at one end ot , 

 the long axis of the opening. The mouth of the shaft is sur- 

 rounded by trees, festooned with creepers which hang down into it, 

 and a mist rises, carried upwards by the return currents of air. 

 The native name of the place is "Ana-ahu" ( = Smoky hole). 

 It would appear that a crack was formed during the upheaval of the 

 island, which has been gradually enlarged at this spot by the action 

 of the stream. 



The volcanic basis of Eua appears to consist very largely of 

 fragmentary accumulations arranged in strata. At the mouth of 

 the " Ana-ahu " (about 020 feet above the sea) the layers are 

 horizontal, and composed of moderately coarse fragments. Between 

 layers of a purely volcanic nature there occur others which are 

 hardened by a cement of calcite, in which, besides the volcanic 

 fragments, foraminifera and other organic remains are embedded *. 



Dr. John Murray finds among the organic remains " many 

 pelagic foraminifera, and pelagic molluscs such as pteropoda and 

 heteropoda ; also a few ostracoda and fragments of bottom-living 

 molluscs. Among the foraminifera Glohigerina rubra and hulloides 

 and other Globigerina3 are most abundant." Dr. Murray concludes 

 that " these rocks were evidently laid down in deeper water" than 

 the limestones investing the volcanic basis. 



■o 



* Slide No. 1268 in the collection at the Woodwardian Museum, Cambridge. 



