78 MIDDLEMIBS: THE GE0L0G2 OF tDAB BTATE. 



quartz-schist owing to secondary crashing along parallel planes. It 

 is generally a rough. " harsh " rock, of pale grey or pink, some- 

 times purple and white, colours. It is occasionally ferruginous, and 

 also occasionally penetrated by quartz veins, hut not by granite 

 veins, like the calc-gneiss except very locally. The bedding is 

 generally obscure, and so cannot be detected in hand specimens 

 or ordinary rock exposures, though in rare instances examples 

 occur of distinct bedding or of vague banding. Sometimes a scarp 

 or dip-slope is plainly indicated. Examples of the hitter are more 

 plentiful near the top of the series where it is passing up into the 

 Phyllite series. Otherwise the rock is vague in all these respects, 

 the obscurity being frequently heightened by a rough, platy 

 structure developed as a coarse cleavage or along lines of shear. 

 No clearly denned base to the series has as yet been discovered. 

 Its upper limits, on the contrary, are in many instances plainly 

 exposed. The thickness probably varies greatly as we go from 

 west to east ; but in any case, owing to the obscurity of the dip 

 and to unknown amounts of displacement, it can only be roughly 

 estimated as possibly between 5.000 and 10,000 feet. 



With the exception of the Delhi Quartzite blocks included in 



the biotite-gneiss. and the lowest beds of the 



Accessory minerals. quartzite seen in conta ct with the latter, 



whose special mineralization, with development of garnet, diopside, 

 wollastonite and calcite, has already been described along with 

 the enclosing Aravalli biotite-gneiss (see p. 27). thin sections 

 under the microscope merely reveal among the irregularly inter- 

 locking quartz areas, varying amounts of minute plates of muscovite 

 and some also of biotite, together with a few small inclusions of 

 plagioclase. There is also a little iron ore and minute zircons. 

 The plates of mica where best developed are arranged in lines 

 cutting indiscriminately through the recrystallised quartz areas. 

 There are in addition occasionally other minute undetermined 

 minerals. In the occasional phyllite layers, sericitic mica is common, 

 and very seldom garnet and sillimanite. 



The chief interest in the Delhi quartzite formation is provided 



by its puzzling behaviour towards the under- 

 Delhi QoarteHe areas. ^ AravalUs / The naturc of i]lis llU8 already 



been partially suggested, but it is now necessary to advance 

 evidence in support of this obtained from the large number of 

 exposures of the formation in our area. We shall investigate this 



