IV 



KOROLEVU SECTION 49 



are a few casts of foraminifera of the " globigerina " type, as indicated 

 in the thin sections. Above this lies a bed of a similar basic tuff, 

 having however a banded appearance from the arrangement of 

 materials of different degrees of coarseness, the finer being t-2 mm. 

 in size, the coarser '4-8 mm. There is little or no carbonate of 

 lime; but occasional tests of foraminifera of the type above 

 mentioned occur in the slide. The basic tuffs here abruptly 

 terminate. They represent the quiet deposition in water com- 

 paratively deep of the products of marine erosion, and of the finer 

 ejectamenta of some distant subaerial vent. 



Above the basic tuffs lie a series of tuffs, about 5 feet in 

 thickness, and composed mainly of the debris of acid andesitic 

 rocks of the hornblende-andesite type, such as occur in the 

 Ndrandramea district. They mark a period of active eruption on 

 the part of some neighbouring acid andesitic vent in this neighbour- 

 hood, which the subsequent explorer may be able to identify with 

 some volcanic " neck." 



These tuffs are composed partly of fragments of a hemi- 

 crystalline hornblende-andesite and partly of crystals, broken and 

 entire, of plagioclase, hornblende, rhombic pyroxene, and augite. 

 The plagioclase is tabular, zoned, and glassy, and gives extinctions 

 of oligoclase-andesine (6 to 12 ). The hornblende is bottle green, 

 markedly pleochroic, and gives extinctions up to 14 . The rhombic 

 pyroxene has the characters described on page 301, in the case of 

 the Ndrandramea rocks. The augite is less frequent, but the two 

 pyroxenes are sometimes associated as intergrowths. 



These acid tuffs do not effervesce with an acid, nor can any 

 tests of foraminifera be observed in them ; but since these organisms 

 are represented in the basic tuffs below, it is highly probable that 

 the whole series of these horizontal beds is submarine. The first 

 or lowest bed of the acid tuffs indicates a somewhat violent 

 volcanic outbreak in this neighbourhood, following the deposition 

 of the basic tuffs. It is composed of loosely compacted subangular 

 fragments, 1 to 3 millimetres in size, in which the macroscopic 

 prisms of the rhombic pyroxene are especially frequent. It passes 

 upward without interruption into a regularly grained sandstone 

 formed of rounded and subangular fragments measuring -3 tc 

 7 mm. across. Above this lies a quite distinct bed, a few inches 

 thick, of a fine compact clay rock, where the mineral fragments 

 measure only -05 to -12 mm. in diameter, hornblende being well 

 represented, although the rhombic pyroxene is very scanty. Up 

 to this time these beds of acid tuffs indicate a gradual defervescence 



E 



