IX THE LAMBASA PLAINS 139 



interstitial glass. The basic rocks prevailing between Vatu-levoni 

 and Vandrani belong to genus 13 of the augite-hypersthene- 

 andesites and have a groundmass of much finer texture, the 

 felspars only measuring -05 mm. Their specific gravity ranges 

 between 27 and 275. 



The overlying foraminiferous and pteropod clay rocks, the 

 so-called " soapstone," are exposed over large areas of the surface. 

 A good idea of the important part they take in the formation of the 

 lower plains may be formed by visiting the hot springs of Vuni- 

 mbele, close to Vuni-moli, which issue from the side of a deep 

 trench cut into these deposits. As generally displayed at the 

 surface, they have been subjected to so much hydration in the 

 weathering process that they appear as yellowish- white clay-rocks 

 deprived of their lime ; and it is only now and then that the 

 remains of foraminifera and pteropods can be detected. They are, 

 however, fairly well preserved around the base of Ulu-i-mbau in 

 the vicinity of Koro-wiri, where they contain, besides the shells of 

 pteropods and foraminifera, portions of decaying coral, and extend 

 to 200 feet and over above the sea. Here they are overlain by 

 rather coarser basic tuffs of mixed character, containing 5 or 6 per 

 cent, of carbonate of lime and some palagonite, which I followed 

 as high as the track lay, rather over 500 feet above the sea.^ The 

 reef-limestones, already noticed as exposed in the low hills between 

 Wailevu and Lambasa, lie a mile or two inland and reach to 100 

 feet above the sea. 



The fragments of siliceous rocks, which with occasional bits of 

 impure Hmonite, occur at intervals all over the surface of these 

 plains and largely form the gravel and pebbles in the river-beds,, 

 include nodules of chalcedony, fragments of jasper or iron-flint, 

 white quartz-rock formed of chalcedonic silica, silicified corals, &c. 

 They are especially frequent in the vicinity of Nasawana and 

 Koro-utari, and include fine specimens of agates and of onyx. 



' I did not ascend to the top of Ulu-i-mbau. It is, however, evidently 

 composed of basic andesitic rocks, occasionally amygdaloidal. On its slopes 

 up to at least 600 feet above the sea occur agglomerate-tuffs and finer submarine 

 tuffs, as above described, overlying foraminiferous clays, a submergence of 

 quite 500 feet being indicated by the investing deposits. 



