Plate VIII. 



Microperthitic structures. 

 Figures i, 2 and 3 show three forms of microperthitic structure frequently 

 displayed by the charnockite series. In fig. 1 large, irregular, vermiform inclu- 

 sions of a striped felspar occur in addition to the finer spindles. In fig. 2 the 

 groundmass is microcline and the microperthitic inclusions are of a felspar having 

 lamellar twinning. In fig. 3 untwinned felspar includes two sets of twinned 

 inclusions. 



Fig. 1 is a photograph of section No. 1442 X 35 diameters. 

 „ 2 „ „ „ „ 1428 X 60 „ 



„ 3 •> »> » »» ^76 x 20 „ 



All photographed with Nicols crossed. 



Secondary alterations. 



Figure 4 shows the Schiller plates in a crystal of hypersthene from coarse 

 charnockite (No. 8,761) obtained near Coonoor, Nilgiri Hills. Section No. 1754 

 magnified by 20 diameters. 



Figure 5 shows the alteration of felspars in a member of the charnockite series 

 which has been invaded by peridotite intrusions in the " Chalk Hills" near Salem. 

 The felspars, except in the immediate precincts of hypersthene crystals, are 

 crowded with minute black inclusions which can be individualized only with a 

 ^0 inch objective. The inclusions are arranged in rows parallel to the twin planes 

 of the felspar. Specimen No. 9*689 j section No. 1791 magnified by 35 diameters. 



Figure 6 shows a spongy garnet corona around hypersthene, with the quartzose 

 by-product forming an intermediate layer between the two minerals (see p. 161). 

 Specimen No. 11,903, Nagaramalai, near Salem. Section magnified by 80 dia- 

 meters. 



