ARAVALLI SYSTEM. 31 



calc-gneiss continuing; in regular sequence above it. On its other 

 side it is* some distance away from the Delhi Quartzite outcrops. 

 N°- 3~s^ (32896) and jjfa (12297) are both specimens from the 

 Medh area of little hills, the former being characterised by a quartz- 

 felspar mosaic with brown biotite plates, such as we have already 

 noticed in the previous example at Damavas, the andesine-labra- 

 dorite being much less in quantity than the quartz. Some of 

 the basal sections of the biotite show sagenite webs as three sots 

 of black lines of (?) rutile needles crossing one another at an anrde 

 of 60°. They are probably secondary in origin, as they accompany a 

 partial bleaching of the dark mica. Pinkish garnet is fairly common 

 in this rock along certain lines in the thin section in ragged granular 

 areas. There is a noticeable amount of short rods of apatite in the 

 rock. The latter specimen ( 3 2 5 , 12297) is very similar generally, 

 but garnet is absent, and, intergrown with the quartz areas, is 

 some pale green, faintly pleochroic, uralitic hornblende in large 

 lagged plates. 



Specimen No. f$\ (12298-9), from south of Wasan in one of 

 the western areas, is remarkable for the large pink garnets (12298) 

 snd areas of quartz rendered dark by swarms of included minute 

 grains of dark green (?) garnet and biotite flakes (12299). 



(3) Aplite and Pegmatite Veins intrusive in the Calc-gneiss and 



Biotite-gneiss. 



In order to complete the geological description of the Aravalli 



Constant association areas occupied by the calc-gneiss and biotite- 



wiih tire calc- and gneiss, it will be desirable now to consider 



hiotito-gneiss. ,, » . . 



the veins of more or less acid aplite material 

 that penetrate them in a very perfect and complicated manner, 

 the penetration being sometimes so complete that the veins have 

 become to all intents and purposes integral parts of these masses, 

 and any description of the one without the other would be unsat- 

 isfactory. (See PI. 1, fig. L and PI. 3.) Furthermore, these aplite 

 veins, though not absolutely restricted to the calc-gneiss and biotite- 

 gneiss areas, still are but seldom found outside those areas among any of 

 the other detached representatives of the Aravalli system. Nor do 

 they as a rule penetrate up into the Delhi Quartzite, and certainly 

 not into anything but its lower beds in the neighbourhood of the 

 underlying biotite-gneiss. The fact, however, that they do penetrate 



p2 



