ARAVALLI SYSTEM. 17 



extinction angles near 0° and 90°. One section in the slice is 

 isotropic and gives the black cross in convergent light. The well- 

 developed prominent cleavage is parallel to the general elongation 

 of these areas, and the axis of lesser elasticity is seen to be at right 

 angles to this, so that the mineral has negative elongation and may 

 be presumed to be negative. The diopside in this rock besides 

 being generally distributed over the rock is also specially aggre- 

 gated along with the sphene into layers an inch or more in thick- 

 ness. Here the diopside, showing bluish-green tints, is charac- 

 teristically developed in good hypidiomorphic lath-shaped and other 

 sections from which, in combination with the cleavages, its optical 

 characters can quite easily be deduced (12139, PI. 9, fig. 1). 



One and a hall' miles south of Gota a specimen, 3 2 K 5 ; 2 , (12140, PI. 9, 

 fig. 2) is remarkable for innumerable small irregular grains and aggregates 

 of grains forming an imperfect mesh work of colourless garnet 

 (grossularite). Quartz and felspar are abundant in this rock 

 There is a fail' amount of hypidiomorphic, distinctly coloured 

 diopside, much sphene and less calcite than usual. Along with 

 the quartz-felspar layers there are long lath-shaped sections of 

 a pale mineral with pearly lustre, a single prominent cleavage and 

 positive elongation. Its moderate refractive index and rather weak 

 birefringence point to wollastonite (see specimen Af^ to follow). 



Prom the calc-gneiss hills east of Golwara comes a rock (A*g, 

 12141, PL 9, fig, 3) from which calcite is almost absent, the dan.er 

 layers being made up very largely of diopside. huge aggregates of 

 granular white garnet (grossularite), some sphene, and. along certain 

 layers a Large amount of the colourless mineral of the last-described rock. 

 It is quite soft under the knife and has a pearly lustre. It appears 

 under the microscope in short lath-shaped sections with one pro- 

 minent cleavage and parallel fibration, giving generally parallel 

 extinctions and positive elongation, a moderate refractive index 

 (not SO high as the diopside) and rather weak birefringence. These 

 data, as in the rock above, point to wollastonite. a conclusion verified 

 by etching with acid and staining on the uncovered thin section. 

 Quartz-felspar layers, in which miorocline is prominent, cut through the 

 rock in fine white vein-like bands, much of the felspar of which has 

 been altered into a brownish, dusty, amorphous, isotropic substance. 



In the sections laid bare in the railway cutting 2 miles S.S.VY. 

 of Khed Brahma, where the more calcareous form of the calc- 

 gneiss is in evidence ($^ 7 to 3 2 4 9 , 12142 to 12146) there occur a few 



