86 A NATURALIST IN THE PACIFIC chap. 



on the way from Nambuna to Ndrawa one passes from the region 

 of the acid andesites into that of the basalts. The track first 

 skirts the base of Mount Wawa-Levu, where the prevailing altered 

 dacitic rocks are exposed in a much decomposed condition in the 

 stream-courses. Then there is a gradual ascent through somewhat 

 broken country to reach the western slope of the table-land, and 

 here are at first displayed the semi-vitreous basaltic andesites just 

 referred to. 



The Wainunu table-land is bisected in a singular fashion by 

 the Ndavutu River. Since, however, the deep and often gorge-like 

 channel of the river displays submarine deposits incrusting the ba- 

 saltic slopes on its sides, it is evident that the break in the basaltic 

 table-land existed in part at least before the emergence. 



With regard to the total thickness of the basaltic flows of this 

 plateau I have only a few data. In the bed of the Ndavutu River 

 opposite Vunivuvundi, and about 400 feet above the sea, there is 

 exposed a greyish porphyritic rock showing pyrites, apparently an 

 altered andesite. If this is the bed-rock, the basaltic plateau in 

 that locality would be 300 to 400 feet in thickness. This is rather 

 over the thickness of the end of the table-land at Masusu. 



I pass on now to consider briefly the submarine deposits that 

 overlie the marginal slopes of this basaltic table-land in places. 

 They are for the most part pteropod and foraminiferous ooze-rocks 

 and are extensively represented on the surface and slopes of the 

 Nandua flat to the north of Ndavutu, where they occur at all 

 elevations up to 500 feet above the sea. They are also displayed 

 on the eastern slopes overlooking the Yanawai but at rather lower 

 heights ; and little patches of them occur here and there in differ- 

 ent places but not exceeding 500 feet in elevation. These friable 

 clayey rocks, which contain from 30 to 40 per cent of carbonate of 

 lime, are described in detail on page 320. It may however be re- 

 marked here that these deposits are but partly derived from the 

 degradation of the submerged basaltic table-land or from the wash- 

 ings of a basaltic coast. They were formed in a clear sea-way, but 

 probably at no great depth, at a time when the basaltic plateau 

 was submerged below the level of breaker-action. 



It is remarkable that these deposits do not repose directly on 

 the basaltic rock. In one place below the Nandua tea-plantation, 

 where there is a steep descent to the river of about 250 feet, the 

 pteropod ooze-rock, which is exposed in the upper half, passes 

 down into a chocolate-coloured marl that contains 5 per cent of 

 carbonate of lime and is horizontally bedded. It is composed in 



