ARAVALLI SYSTEM. 37 



being intrusive in the calc-gneiss, arc also typical medium-grained 

 grey rocks with abundant quartz and microcline, and very scarce 

 little nests of vague ferro-magnesiazi minerals, probably mainly 

 biotite and hornblende in intimately parallel intergrowths. No 

 iron ore. There is a very little of a mineral appearing in highly 

 dichroic elongated sections with parallel extinctions and moderate 

 double refraction. The direction of least elasticity is at right angles 

 to the elongation, and vibrating in this direction the transmitted light 

 is a deep indigo-blue, whilst it is colourless in the other direction 

 at right angles to this. The mineral is referred to tourmaline 

 (indicolite). 



Specimen £& (12323. PI. 10, fig. •!), from 1 mile N.W. by N, of 

 Medh, is a coarsely graphic pegmatite composed chiefly of 

 microcline and quartz, but with patches of small, zoned tourmaline 

 needles and prisms, giving pleochroism which is colourless for 

 vibrations parallel to the elongation and yellowish and bluish-green 

 at right angles to this. There are a few colourless garnets and 

 some matted bundles of slender prisms of sillimanite running through 

 the quartz. A little plagioclase — albite-oligoclase (?) — and no iron 

 ores. Specimens g 2 8 9 7 and 3 2 8 '' 8 from the hills south-east of Khed 

 Brahma are coarse graphic pegmatites with much garnet and black 

 tourmaline. 



Syenite Afliies. 



The vein aplites that are grouped under this heading, without 

 being sharply distinguished from the granite-aplites, nevertheless, 

 as a whole, contain less potash felspar and quartz and more plagio- 

 clase, whilst the dark minerals arc more consistently represented 

 by diopsidc, or diopside in addition to uralitic hornblende and other 

 alteration products, and a certain amount of biotite. Sphene also 

 becomes a far more common accessory. 



The following specimens may be taken as typical of this class 

 of aplite intrusive in the calc-gneiss : Nos. .^\ (1232-1) and JA 

 (12325), from localities respectively 2 miles N. by E. and hills S. 

 of Khed Brahma, appear almost identical in the hand-specimen, 

 but the question of the class of felspar is not clear in the former ; 

 microcline is quite certainly the dominant mineral, basal sections 

 showing the ' grating ' structure with extinctions of 15° with the 

 lamellec, whilst in sections giving nearly rectangular cleavage and 

 which must be at right angles to (001) and (010), and in which also 

 only one set of twin lamellae appear, the extinction angle with the 



