ARAVALLI SYSTEM. 29 



gneiss, especially at the southern and more elevated end. The 

 biotite-gneiss is also seen in the river cliff at Derol ( 4 2 9 5 )- ^ n tne m ^ 

 north of Derol a section is as in text fig. 5 but the arrangement 



Fig. 5. 



east of this becomes considerably confused, and suggestive of an 

 irregularity of some sort at the junction. Though there is no ex- 

 posure of included blocks along the junction, the Delhi Quartzite 

 coming above the gneiss ( 3 2 7 9 5 , 12293) shows, under the microscope, 

 many characteristics of a contact-affected rock, including granular 

 and irregular areas of garnet, diopside, zoisite and minute zircons. 

 There is also some calcite, and the whole mass of the interlocking 

 quartz mosaic is dusky with crowded minute inclusions. 



In examining the thin sections of these and many related rocks, 

 one is much struck by the general similarity of appearance of many 

 of the minerals when viewed in ordinary transmitted light. Owing 

 to the lack of distinctive colouring, the frequently granular shape 

 and practically identical refractive index and consequent relief, the 

 garnet, diopside and zoisite all resemble each other exceedingly. 

 It is only with polarised light and higher magnification powers that 

 the characteristic birefringence, position of the axes of elasticity 

 and cleavages enable one to separate them into their proper species. 



After crossing the Harnav river, south of Derol, there is a small 

 exposure of the biotite-gneiss to the south- 



Damavas outcrops. * . __ . . ° . 



east or Kalol, and then the interesting exam- 

 ples near Damavas next claim our attention. The 858 ft. hill, 

 | mile E.N.E. of Damavas is a bare little prominent hill which, 

 viewed from the south, is as seen in PI. 8 and in outline in text fig. G. 

 The biotite-gneiss (^ 6 , 12294. PL 9, fig. 6) is of greyer tint than 

 that at Dijio, with a finer foliation and much contorted or puckered 

 on a small scale. It is invaded by striking veins of biotite-aplite 



D 



