BY W. G. WOOLNOUGH. 459 



viii. — Wailoa and Nadarivatu District. 



The Wailoa River (Black River, so called on account of the 

 abundance of magnetite sand and limburgite gravel in its bed) 

 is the principal tributary of the Wainiinala River. It rises in 

 the southern slopes of Tomanaivi, the highest point in Fiji, and 

 flows in a general S.S.E. direction, joining the main stream just 

 below the town of Udu. 



Nadarivatu is situated immediately on the northern edge of 

 the high plateau which extends here within a few miles of the 

 north coast, and in places actually reaches the coast. It lies at 

 an altitude of about 2600 feet above sea-level. 



The whole area included in this section is characterised by a 

 remarkable development of extremely basic limburgitic lava, and 

 associated tuffs and agglomerates. These form practically the 

 universal surface-rocks of the district. 



Eastwards they pass into the level-bedded '' soapstone " tuffs 

 of the Waiiiibuka. These soapstones, which are gently dipping 

 in places, extend from about Nubumakita right away to the 

 north-east coast apparently. It is extremely probable that they 

 represent the actual extension of the limburgite series, beyond 

 the eastern limit of its solid lavas. 



Towards the south the area is bounded fairly sharply by the 

 Wainimala, which, about Udu, suddenly turns east after flowing 

 north for a long distance. The more or less linear boundary of 

 the basic series, corresponding as it does with this sudden change 

 in direction of a main river-valley, certainly points to some major 

 earth-structure; but evidence as to its exact nature is wanting. 



Northwards the area reaches the sea at a point north-east of 

 Nadarivatu. To the north-west of Nadarivatu there is a very 

 sharp drop of 2000 feet to the village of Waikubukubu, whence 

 a coastal plain, some eight or nine miles wide, slopes to the mouth 

 of the Tavua River. This coastal plain was described in mv 

 former paper (p.478), and it was there inferred from the crateri- 

 form shape of the numerous hills which cover it, and from the 

 evidences of extinct hot spring action, that volcanic activity has 

 only comparatively recently died out in this portion of the island. 



