330 ME. T, H. BURTON ON THE MICEOSCOPIC [vol. Ixxiii, 



The grains are often flattened and smooth. The average maxmium 

 diameter of the majority of quartz-grains is about 0-51 mm. 



Inclusions are: — (1) Regular; as tourmaline, rutile, apatite, sillimanite, 

 biotite. 



(2) Irregular ; as gas and fluidal cavities, glass. 



(3) Acicular ; as tourmaline needles, liair-like inclusions, 



and fine needles — probably rutile. 



Tourmaline, especially the brown kind, occm-s abundantl}^, 

 mainly in the form of more or less rounded gi*ains (a few appear 

 perfectly spherical), and in well-worn, mostly stout prisms. Nearly 

 colourless, blue, green, and mauve grains are present. The blue grains, 

 are often ver}^ worn and rounded. The average diameter of rounded 

 grains is about 024i mm. Frequent inclusions of an opaque 

 mineral without crystal outline occur. Less frequent are fluid, 

 glass, and occasionally rods and needles, resembling sillimanite. 



Ilmenite and leucoxene. — The former mineral is plentiful; 

 while the latter is very abundant, and may be derived either from 

 ilmenite or from titaniferous magnetite.^ Some ore of iron, in 

 most eases decomposed and resembling leucoxene, is attached to 

 quartz, and is quite common. Iron-sand ^ is the most plentiful 

 form in which ilmenite is present. 



Micaceous ilmenite occurs sparingly. Its colour is light 

 reddish-brown. The plates enclose rutile-needles, which are inter- 

 laced in the form of sagenite at an angle of 60°. 



Zircon. — This mineral is abundant, generally colourless, and 

 occm's mostly in well-defined, though more or less worn crj'stals. 

 Almost spherical grains are not infrequent ; a small proportion is 

 unworn. The length ranges from about 0'07 mm. up to 30 mm. 

 Some pale-yellow grains resembling monazite, which I take to be 

 zircon, are not uncommon. Inclusions are frequent, consisting of 

 negative crystals, gas-enclosures, and what appears to be apatite. 



E, utile is fairly plentiful, and occurs mostly in rounded grains 

 and rather stout, worn prisms. A few grains are fragmentary, but 

 show definite signs of wear. The colour varies from yellow to deep 

 amber-red. Both geniculate and polysynthetic twins are present. 



Anatase occurs sparingly. It is found in well-formed plates 

 parallel to (001), also attached to decomposed ilmenite. It varies 

 from colourless to pale yellow. The plates- are not worn. The 

 smallest size noted is O'Oo mm., the largest size 0*10 mm. 



Staurolite"^ is very abundant. One might almost call it the 



1 J. J. H. Teall, 'British Petrography' 1888, p. 167. 



'^ M. F. Heddle, • Mineralogy of Scotland' vol. ii (1901) Supplem. p. 197, 



■* Excellent figures of some Triassic heavy minerals may be found in 



Dr. H. H. Thomas's papers, Q. J. G. S. vol. Iviii (1902) pis. xxxi-xxxii and 



ibid. vol. Ixv (1909) pi. xii. 



