132 A NATURALIST IN THE PACIFIC chap. 



of palagonitised materials and of minerals (pyroxene) such as are 

 abundant in the rock below. In places the grains of the mosaic 

 are bordered by brown and black iron oxide. It would, therefore, 

 appear that a metamorphism has been in operation here, and that 

 the process which began with the recrystallization of the matrix in 

 the lower rock is almost completed in the overlying thin layer 

 where even most of the non-calcareous materials have disappeared. 

 No evidence suggestive of contact-metamorphism came under my 

 notice in this locality. These foraminiferal limestones are surface 

 formations, and it was in the uppermost portion that the metamor- 

 phism was most complete. We here witness in operation the trans- 

 formation of a rock containing 46 per cent, of carbonate of lime 

 (the residue of minerals, palagonite, &c), into a marble or crystal- 

 line limestone. I gather that as in the instance of several of our old 

 British limestones the change is a purely interstitial one, and is not 

 connected with thermal metamorphism. 



These remarks on the basaltic plains of Sarawanga and on 

 their incrusting submarine deposits may be concluded with a brief 

 reference to the siliceous concretions, 2 or 3 inches across, the 

 silicified portions of corals, and the fragments of clay iron-stone and 

 limonite resembling haematite, that occur frequently on the surface. 

 They are common on the plains south of Lekutu and between Lekutu 

 and Sarawanga, and up to elevations of 200 feet in the foraminiferous 

 clay district east of Sarawanga, where fragments looking like por- 

 tions of the silicified branches of Madrepores are to be found ; but 

 they are not limited to such localities, and may occur also where 

 the surface is formed of decomposed basaltic rock. (These matters 

 are generally discussed in Chapter XXV.) 



The Basaltic Plains of the Ndreketi. — This low-lying 

 region of rolling " talasinga " country now serves as the basin 

 of the Ndreketi river, the largest of the rivers of Vanua Levu. It is 

 usually elevated between 100 and 300 feet above the sea, and its 

 limits are well defined by the 300 feet contour line in the map of 

 the island. On the east it is separated from the basin common to 

 the Wailevu and Lambasa rivers by the Sealevu Divide, which 

 is described on p. 136. On the west, as before observed, it is only 

 in part distinguished from the basin of the Sarawanga by the spur 

 descending from the dacitic mountains of Ndrandramea. It meets 

 the coast in the vicinity of the mouth of the Ndreketi ; but for 

 two-thirds of its length it is cut off from the sea by the great 

 Nawavi range. It supports the characteristic vegetation of the 

 " talasinga " or sun-burnt land. Whilst the Pandanus and the 



