SO-CALLED " SOAPSTONE OF FIJI. 6 



and bottom forms of Foraminifera." Further, this Suva deposit 

 corresponds pretty closely to the first subsection of the class referred 

 to, which includes " friable rocks, containing from five to twenty 

 per cent, of carbonate of lime, and displaying to the eye only the 

 white specks of minute Foraminiferous tests with a few of macro- 

 scopic size, such as Cristellaria cultrata and Nodosaria soluta, 

 MoUuscan shells being rarely observed." 



The Suva deposit, in its typical condition, is exceedingly friable 

 and easily disintegrated. It varies in colour from nearly white to 

 dark grey, generally speckled more or less with minerals of darker 

 hue. Under the microscope it presents the characters of a fine 

 siliceous mud, with crystals and grains of augite, hornblende, 

 felspar, and sometimes magnetite, together with sparsely scattered 

 tests of Foraminifera. Its chemical composition varies within 

 certain limits, but may be roughly stated as about 50 per cent, 

 silica ; 18 per cent, alumina ; 5 or 6 per cent, lime and magnesia ; a 

 variable quantity (from 3 to 8 per cent.) ferric oxide ; and 16 per 

 cent, water ; with a small proportion of alkalies, chiefly potash. The 

 lime and magnesia exist mainly, if not entirely, in the form of 

 silicates, and the rock gives off no appreciable quantity of carbonic 

 acid on treatment with acids. 



Intercalated with beds of this typical description are layers of a 

 white and also of a lilac or purplish tint, differing somewhat from 

 the rest in physical characters. The whiter variety is harder and 

 more compact, and gives a more or less conchoidal fracture. Treated 

 with water, it is easily broken up into small angular lumps, but does 

 not readily disintegrate further. Its chemical composition does not 

 differ materially from that of average samples of the common 

 variety. It contains rather less alumina, iron, and silica, some- 

 what more lime and magnesia (a portion existing as carbonate), and 

 a larger percentage of combined water. 



The dark-coloured, lilac, or purplish bands resemble an exceed- 

 ingly fine sandstone, though by no means uniform in texture.. This 

 sort is hard and difficult to disintegrate. A fragment, on analysis, 

 yielded nearly 60 per cent, silica and 20 per cent, alumina. Micro- 

 scopical sections revealed a few pelagic Foraminifera, but were other- 

 wise devoid of organisms. 



In addition to the foregoing, the deposit contains small veins of 

 iron-pyrites. 



My attention has been chiefly devoted to the common, grey, friable 

 rock which forms the bulk of the deposit, and especially to its 

 microscopic fauna. Material of this description cannot be studied 

 with advantage by means of transparent sections. Thin slices of 

 geological deposits even less cohesive than these may readily be made 

 by hardening the material in the first place with a resinous varnish, in 

 the manner described by Mr. Pearcey* ; but microscopical sections 

 of the Suva rock, so prepared, were chiefly serviceable in showing 



* Proc, E. Phys. Soc. Edinb. vol. viii. p. 296, pi. 11. Mr. Pearcey has been 

 good enough to prepare sections of these and some similar rocks for me by his 

 method. 



b2 



