STRATIGRAPHICAL ELEMENTS: CRYSTALLINES, ETC. 73 



the portions of these layers which still retain their original molecu- 

 lar structure shew up clearly by extinguishing light more or less 

 simultaneously over their whole area ; on the other hand the 

 intervening bridges of material, that have been crushed and 

 reunited, shew a complicated mosaic with aggregate polarisation. 

 The quartz layers give evidence of the same rolling-out process. 

 Both brown and white micas are represented, the latter predominat- 

 ing slightly. They follow along the foliation, wrapping round the 

 eyes of felspar in a way that must be seen to be believed. A more 

 perfect example of this structure than the present specimen affords 

 could not be imagined. Garnets may here and there be detected by 

 their isotropic behaviour, etc., but they have been cracked and 

 broken and rolled out into lenses just as have the quartz and felspar. 



Plate I, figs. 1 and 2, are photographic reproductions of draw- 

 ings of a slice of this rock in natural light and between crossed nicols 

 respectively. The large crystal at the top represents a singly twin- 

 ned felspar, cut through by cracks which have displaced the line of 

 the composition face. The rolled-out layers of quartz are well seen 

 on the right, and an elongated and crushed garnet is seen in the cen- 

 tre with its lower extremity drawn out into a number of lozenge- 

 shaped fragments. 



The above rock, if compared with the description and drawing 

 of the Beinn Vuroch gneissose-granite (seeTeall's Brit. Petrography 

 p. 325 and PI. XL III), will be seen to be almost identical with it. 



No. -g-fj, from the same locality as the last. In the hand-specimen 

 the beautiful glassy felspars, almost meriting the name of sanidine, 

 exhibit carlsbad twins in perfection, notwithstanding the deformation 

 by pressure which they have suffered. Generally the rock resembles 

 the last described, but the mica is more prominently visible, and there 

 are more garnets. There are a few grains of plagioclase present, but 

 no microcline structure. 



No - si?r> ri g nt bank of Indus river west of Ghazikot. A lenticular- 

 tabular foliated variety. It is a more thinly foliated rock and shews 

 a slightly more complete pressure deformation of the flaser type 



( 73 ) 



