BY 11 I. JENSKN. 97 



Texture: almost holocrystalline, uneven-grained, consisting of 

 crystals of various sizes (all niicroscopic) ranging down to 

 interstitial isotropic matter. The fabric is a variety of 

 pilotaxitic, very close to panidiornorphic-granular. 



Composition : the main constituent is felspar, the crystals of 

 which exhibit shadowy extinction, and Carlsbad twinning. The 

 refractive index is very slightly below that of Canada balsam. 

 The felspars are mostly tabular in habit, and almost idiomorjihic, 

 fitting Ijeautifully into one another as in a mosaic. They consist 

 chiefly of anorthoclase, but a little albite and oligoclase appear to 

 be present also. Baveno and Manebach twinnings are present 

 in some crystals. 



Pyroxene is wholly absent, but a j'ellow mineral takes its 

 place. This mineral is pleochroic from greenish-yellow to honey- 

 yellow; it has a high refractive index, and a medium double 

 refraction (about 0-018). It appears to be optically positive. 

 Complex twinning is occasionally seen in it, and extinction is 

 straight with the cleavage. It is sometimes stained with yellowish 

 or brownish decomposition-products. Some of the small grains 

 are square, and exhibit rectangular cleavage; others seem to have 

 pyramidal terminations. It is probably a tetragonal mineral, 

 isotropic sections being met with. One of its most remarkable 

 properties is, that numerous individual grains of it lying within 

 certain areas are optically continuous so that the felspar is 

 ophitically embraced in it. In optical properties this mineral is 

 nearest to meliphanite. Mr. Wright, Assistant Demonstrator 

 in Chemistry at the University, has found berjdlium in the rock; 

 but in other respects, as, for example, the high TiOo, the rock- 

 composition would indicate that this mineral must belong to the 

 lavenite group. There is no other mineral piesent which is rich 

 in titanium; hence in this unknown mineral we must include the 

 following molecules as determined from the norm: acmite 5-08, 

 hypersthene 0*20, titanite 4-12, ilmenite 0-15. 



Another yellowish-brown mineral present in the rock exhibits 

 no pleochroism, and shows sometimes a fibrous radial structure. 

 It is almost isotropic and appears to be chalcedony. Hiematite 



