XV MBUTHAI-SAU VALLEY 219 



clayey material, and on the other into an agglomerate formed 

 of angular blocks of vesicular and compact basalt with the 

 interstices filled with pale yellow tufaceous material. 



East of the Avuka Range that limits the Lambasa plains on 

 this side is the picturesque valley of Mbuthai-sau. This broad 

 valley runs in a south-east direction into the heart of the island. 

 So small is the gradient that the river flowing down it can be 

 ascended in boats for some miles ; whilst Ngele-mumu, a village 

 situated between 5 and 6 miles up the valley, is not much over 

 50 feet above the sea. This valley in its lower part roughly 

 divides the regions of acid and basic rocks that lie east and west 

 of it respectively. It has, however, been above pointed out that 

 the two regions overlap in the coast region on the west side of the 

 valley. The two types of rocks are also associated in the coast 

 hills immediately east of the valley, since when striking inland 

 from Lloyd Point to the Mbuthai-sau sugar-cane district, one 

 leaves behind the acid rocks at the coast and traverses a region of 

 basic agglomerates. With these qualifications, therefore, the above 

 line of demarcation holds good. 



(2) The Sea-border between the Mbuthai-sau and the 

 Langa-langa Rivers 



The rocks predominating in this district are white and pale- 

 yellow pumice-tuffs and pumice agglomerates, with quartz-por- 

 phyries and oligoclase-trachytes as intrusive masses. The light 

 colour of the sea-cliffs, thus composed, makes them conspicuous 

 from seaward. Their appearance evidently led Mr. Home into an 

 error in 1878 when he viewed this coast from his canoe during his sea- 

 passage from Lambasa to Tutu. " The coast from Lambasa " — he 

 says — " is a series of bold projecting bluffs of agglomerate inter- 

 spersed with seams of coralline sandstone." ^ The principal feature 

 of this coast, however, is the prevalence of light-coloured pumice- 

 tuffs, though it is not improbable that elevated reef-formations may 

 occur in some localities. 



I particularly examined the coast districts in the vicinity of the 

 Wainikoro and Langa-Langa rivers. In a spur that descends to 

 the right bank of the river, a little above the mouth of the Waini- 

 koro, is exposed an open-textured rhyolite or quartz-porphyry 

 containing, as described on page 310, phenocrysts of glassy felspar 

 (oligoclase and sanidine), quartz, and a little hornblende. Some 

 ^ A Year in Fiji, p. 22. 



