OF THE TONGA ISLANDS. 605 



covered by about two feet of water. In some places, however, there 

 are the remains of the shore-platform which was formed when the 

 ishmd stood at a lower level, and corresponds with the hij^her line of 

 undermining- seen in the cliffs above. Its upper surface is above 

 the level of hij^h water, and is worn into irregular shapes. It is 

 overgrown in some places by a small shrub (Pemphis acidula). 



These features jjoiut clearly to recent elevation, and the distance 

 between the two lines of undermining seen on the cliff shows that 

 the extent of this was 7 feet. Further, it is clear that the eleva- 

 tion took place rapidly, at least as mcnisured by the rate at which 

 the sea is wearing back the cliffs, for if it had been accomplished 

 slowly, in com])arison with that measure, the rock which forms a 

 projecting ledge between the two levels of excavation would have 

 been woi-n back during the elevation. 



It is interesting also to note that if the island were to remain at 

 the level it occupies at present, all traces of the recent elevation 

 would in time be obliterated, for as the cliff was worn back the rock 

 beaiing the impress of the action of the waves when the island was at 

 the lower level would be removed, while the remnants of the older 

 reef-platform would be worn away to the level of the present one. 



It may further be observed that a reef-platform such as this consists 

 of two distinct parts — an outer formed by the growth oubwards of 

 the existing reef, and an inner formed of the base of the older and 

 elevated reefs, whose higher portions have been removed by the 

 action of the sea. 



At the south end of the island there is no reef; deep water 

 extends to the foot of the cliffs. 



A narrow fringing reef, some hundred yards wide, extends along 

 the eastern side of Eua. Its upper surface is above the level of 

 high water and partly worn away by the sea, offering evidence of 

 the recent elevation of the island, corresponding to that found on 

 the western shore. The margin of the reef is exposed to the full 

 force of the rollers coming up before the trade wind, and presents a 

 remarkable basin-like growth of corallines similar to that found on 

 the southern side of Tongatabu, to be described later. 



At the south end of the eastern shore of Eua there is a remark- 

 able instance of the different manner in which the volcanic and 

 limestone rocks are excavated by the action of the waves. 



A narrow terrace, perhaps a quarter of a mile broad, runs 

 round this end of the island, standing at a level of some 240 feet 

 above the sea. It is bordered by cliffs which go sheer down into 

 deep Avater. Limiting it on the land side there is a steep ascent 

 to a higher terrace above. 



The limestone rock here lies on the steeply sloping surface of the 

 volcanic basis of the island. The outer or sea border of the 

 terrace and nearly the whole face of the cliff are formed of lime- 

 stone ; but at the inner border of the terrace, and here and there 

 in the lower part of the cliffs, the volcanic basis is exposed. At 

 one point there is a large circular chasm excavated in the terrace 

 which descends to sea-level and communicates with the sea by a 



