134 



THE VOYAGE OF H.M.S. CHALLENGER. 



rather common. Fibro -radiated zeolites often occur in the vesicles, and are also 

 disseminated throughout the rock. A specimen of this phonolite has been analysed by 

 Dr. Klement, with the following results : — 



I. 1'0730 grammes of substance, dried at 110° C. and fused with the carbonates 

 of soda and potash, gave 0'0387 gramme of water, # 5887 of silica, 0"2322 of alumina, 

 0"0461 of ferric oxide, 0"0175 of lime, 0"0110 of magnesium pyrophosphate, and traces 

 of manganese. 



II. L0285 grammes of substance, treated with hydrofluoric acid, gave 0'2448 

 gramme of potassium and sodium chlorides, and 0"2130 of potassium chloroplatinate. 



III. 1*2168 grammes of substance, treated with hydrofluoric and sulphuric acids in 

 a sealed tube, was titrated with potassium permanganate and recpiired for oxidising the 

 ferrous oxide 2 c.c. of solution (l c.c. = 0"005405 gramme ferrous oxide). 



Percentage Composition. 



99-60 



This analysis confirms the determination of the rock as phonolite, the large 

 percentage of soda corresponding well with the important part taken by nepheline. 

 The water present proves the alteration of the rock, which is also indicated by the 

 zeolites disseminated throughout the whole mass. 



Another nepheline rock picked up in the centre of the same creek differs con- 

 siderably in mineralogical composition from the preceding. It is darker coloured, 

 coarser in grain, marked with opaline points, less schistoid in structure, spotted with 

 small deep green prisms, and sometimes speckled like the phonolite described above. 

 A paler grey-green specimen is very massive, and no mineral can be distinguished 

 by the naked eye ; it has a very distinct prismatic fracture. The greyish ground- 

 mass is formed exclusively of little crystals of nepheline. In this there appear distinct 

 green lamellar sections which are pleochroic, as it were corroded, and including 

 nepheline crystals. The mineral might be taken for hornblende were it not for its 



