IV KOROLEVU SECTION 



49 



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

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

 laving however a banded appearance from the arrangement of 

 naterials of different degrees of coarseness, the finer being •1-2 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 

 t lickness, and composed mainly of the debris of acid andesitic 

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

 ^'drandramea district. They mark a period of active eruption on 

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

 fa Dod, which the subsequent explorer may be able to identify with 

 some volcanic "neck." 



These tuffs are composed partly of fragments of a hemi- 

 ciystalHne hornblende-andesite and partly of crystals, broken and 

 ei tire, of plagioclase, hornblende, rhombic pyroxene, and augite. 

 T le plagioclase is tabular, zoned, and glassy, and gives extinctions 

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

 m irkedly pleochroic, and gives extinctions up to 14°. The rhombic 

 P) roxene has the characters described on page 301, in the case of 

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

 p>roxenes are sometimes associated as intergrowths. 

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

 Ite.' ts of foraminifera be observed in them ; but since these organisms 

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

 th( whole series of these horizontal beds is submarine. The first 

 or lowest bed of the acid tuffs indicates a somewhat violent 

 vo. canic outbreak in this neighbourhood, following the deposition 

 of ;he basic tuffs. It is composed of loosely compacted subangular 

 Fra jments, i to 3 millimetres in size, in which the macroscopic 

 3ri ;ms of the rhombic pyroxene are especially frequent. It passes 

 apvard without interruption into a regularly grained sandstone 

 j:or ned of rounded and subangular fragments measuring -3 to 

 \7 1 im. across. Above this lies a quite distinct bed, a few inches 

 hi( k, of a fine compact clay rock, where the mineral fragments 

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

 ep esented, although the rhombic pyroxene is very scanty. Up 

 O; t !iis time these beds of acid tuffs indicate a gradual defervescence 



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