ix TAMBIA 



i37 



and indicates the antiquity of the volcanic rocks in this locality. 

 Farther along the coast the typical agglomerates occur, where the 

 blocks, 3 to 10 inches across, are composed of the usual semi- 

 vitreous black basaltic rock showing plagioclase phenocrysts. 

 Nearer Middle Point a decaying doleritic basalt is displayed at 

 the surface. It is similar to the prevailing rock of the Ndreketi 

 plains, and is referred to the ophitic rocks forming genus 9 of the 

 augite-andesites. 



The elevated promontory of Middle Point is a prolongation 

 of a spur of Ulu-i-sori. Where it is crossed by the road it is 

 about 350 feet above the sea. On its west slopes are exposed 

 yellowish-white tuff-like rocks, evidently the prevailing basic clay- 

 tuffs which have become bleached through the hydration accom- 

 panying the weathering process. Beneath these deposits lies an 

 amygdaloidal augite-andesite which is bared in places. The rock 

 is semi-vitreous and the amygdules it contains are often a centi- 

 metre long. They are composed of a white mineral with fibro- 

 radiate structure and made up of needle-like prisms. It gives off 

 water, but it is not easily fused, and does not gelatinise in HC1. 



From the top of the promontory the road strikes inland in an 

 east-south-east direction for Tambia, passing inside the coast 

 range, which is here 600 feet in height, and descending gradually 

 through a region of basaltic andesite into the valley of the Tambia 

 river. (This rock, which has a specific gravity of 2S4, displays 

 more or less parallel stout felspar-lathes, '23 mm. in length, and 

 has a little interstitial glass. It belongs to genus 13 of the augite- 

 andesites.) Low hills shut in the little valley on all sides except 

 where the river breaks through the coast range. The town of 

 Tambia is not over 100 feet above the sea. About a mile to the 

 north exist hot springs of considerable extent which are described 

 on page 32. 



The road from Tambia to the Wailevu River traverses an 

 undulating district varying from 100 to 300 feet above the sea. 

 A basalt containing a little olivine, with a specific gravity of 2*91, 

 is commonly exposed at the surface in a disintegrating condition. 

 Here and there occur basic tuffs. In one locality, there is displayed 

 a dyke-like mass in a small stream course, 200 feet above the sea, 

 of an altered grey and compact andesite marked with parallel red 

 streaks or bands. It is an aphanitic augite-andesite ; and is to be 

 referred to genus 13 of the augite sub-class. It displays closely 

 crowded felspar-lathes, 'oy mm. in length, in flow-arrangement. 

 The bands are due to the gathering of the residual glass in streaks 



