xiv LEA BAY 199 



Passage, elevated reef-limestones, forming low cliffs 6 to 8 feet 

 high, together with occasional tuff-agglomerates, occur at the coast. 



The Lea Sub-District. — This region, which includes the 

 mountain-range of Ngalau-levu at the back of Lea, is limited 

 by Fawn Harbour and Vunilangi Inlet on the south coast, and by 

 the Ndreke-ni-Wai River and a point between Viene and Lea on 

 the north coast. Its structure, as is shown below, is very compli- 

 cated, acid and basic rocks being associated in a remarkable 

 manner ; whilst over all lie the submarine tuffs. Marine and sub- 

 aerial denuding agencies have shaped and re-shaped the surface 

 to such a degree that it is now impossible to restore it in 

 imagination. 



On the north coast of this sub-district, about two miles east of 

 Viene, is exposed an altered darkish porphyrite displaying large 

 opaque crystals of plagioclase, 5 to 7 mm. long, the rock-mass 

 being penetrated by fine veins of chalcedonic quartz, which also 

 traverse the phenocrysts. Its specific gravity is 2*6 ; but on account 

 of the imperfect development of the felspar-lathes and the amount 

 of altered glass in the groundmass, which also contains a little 

 calcite, it can be only generally referred to the augite-andesites. 

 A greenish altered foraminiferous tuff showing fine cracks filled 

 with chalcedony composes a spur in this locality. A propylitic 

 or highly altered dolerite is exposed half-way between Viene 

 and Lea. 



As one nears Lea from the west the lofty spurs of the mountain 

 of Ngalau-levu reach the coast, and basic tuffs and agglomerates 

 prevail. The blocks in the agglomerate are composed of a vesi- 

 cular semi-vitreous hypersthene-augite andesite, which is assigned 

 to the second prismatic sub-order, since it carries prismatic 

 pyroxene in the groundmass. The town of Lea is picturesquely 

 situated on the coast at the foot of the steep mountain-slopes, being 

 closed in on the east and west by elevated spurs descending to the 

 sea. Fragments of jasper and chalcedony occur in the beds of the 

 streams that here drain the precipitous sides of the range. Two 

 dykes of dark basic rocks protrude through the beach in Lea Bay. 

 They are composed of augite-andesites referred to genus 1 3 of the 

 augite-class ; but the two rocks belong to different species of that 

 genus. In the one the felspar-lathes are only -04 mm. in length, 

 and there is a little altered glass in the groundmass, the specific 

 gravity being 2-63. In the other the felspar-lathes average -2 mm. 

 in length, and the rock has a coarser texture, whilst the specific 

 gravity is 27. The augite granules are large ('03 mm.), and there 



