358 ME. H. E. MILXER OX THE [vol. Ixxvili, 



quartz, which in the case of the sands constitutes about 94" 1 per 

 cent, of the facies ; associated Avith the quartz are kaolin, mus- 

 covite. glauconite, and authigenic matter, chiefly limonite in the 

 yellow sands, and haematite in the red sands. In the clays the 

 percentage of mica and kaolin is higher, though much of the 

 material is an indeterminate ' paste.' probably consisting of cpiartz, 

 sericite. chiastolite, rutile, and iron -ores ; the mottling of these 

 clays is due to yariations in the degree of secondary oxidation 

 undergone by the original iron -compounds. 



Description of the more important Mineral Species. 



Quartz. — This mineral occurs in subangular to well-rounded grains, 

 usually" coated with ferruginous cement. On clarification with acid, the 

 grains are seen to be highly turbid, owing to inclusions of apatite, tourmaline, 

 and rutile. Xo fluid cavities were noted in the grains. 



Muscovite. — Varies considerably in composition. The ' light ' material 

 (S.G.<2*82) presents fairly-clear irregular flakes of low polarizing character, 

 usually showing good interference-figures. The denser facies which sinks in 

 bromoforra is turbid with inclusions of ferric oxide, tending to parallel 

 arrangement within the flakes. 



Magnetite is a noteworthy constituent of all facies of the deposit, and 

 occurs in subangular grains ; rounded octahedra are rare, though noted more 

 in the red sands than in the other facies. In the clays, sharply angular 

 fragments are seen (mag-netite dust), of a brilliant silvery-grey colour by 

 reflected light. 



Ilmenite. — Owing to the absence of well-individualized magnetite, some 

 little difiiculty is experienced in differentiating ilmenite from that mineral ; 

 the abundance of leucoxene in the non-magnetic residue, however, is some 

 measure of the proportion of original ilmenite, though in many cases rounded 

 irregular grains of the species are clearly defined by their dull reddish-grey 

 lustre in reflected light. 



Tourmaline is exceedingly abundant, and in the yellow and red sands 

 constitutes the greater part of the residiie. It usually occurs as large, 

 irregular, and rounded grains, of blue, green, brown, intermediate shades, 

 and parti-coloured. The bro^vTi varieties show the strongest pleochroism, 

 and many of the grains, being basal, exhibit uniaxial interference -figures. 

 Besides the grains (though by no means so common), well-formed prisms are 

 seen, generally striated, and having rhombohedral terminations and basal 

 partings ; doubly terminated varieties are rare. Such prisms are usually 

 blue, green, or bluish-green, and are pleochroic : they have an average 

 length of 0'3 mm., while the grains frequently measure 0"25 mm. along 

 their greatest length. 



Staurolite. — Only a few grains of indubitable staurohte were recognized, 

 although the mineral may actually occur in greater proportion, or at least 

 with more constancy than is to be inferred from the determinations made. 

 The grains are well rounded, but characterized by their deep brownish-yellow 

 colour, making distinction between them and the abundant brown tourmaline 

 a difiicult matter. The weaker pleochroism and higher refractive index than 

 the tourmaline were noted ; but the most reliable differentiating factor was 

 the biaxial positive interference-figure revealed in some cases. 



Leucoxene. — Abundant and occurring in dull whitish-grey pellets (as 

 seen by incident light), well rounded, with occasionally a core of unaltered 

 ilmenite. The grains have a rough and pitted appearance, and are frequently 

 stained brown. 



