64 GEOLOGY OF THE SON VALLEY, ETC. 



beds dip 15 W, of S. at S5 and are very much contorted as 

 may l»e seen even in the hand-specimen. The rock has a light 

 silvery blue colour with bright ferruginous ruddy stains in irregular 

 bands. Under the microscope the rock is seen to consist of exceed- 

 ingly minute sand particles consisting mainly of quartz with a few 

 equally small grains of tourmaline. There are many minute flakes 

 of brightly polarising white or pale-green mica. The section also 

 shows white opaque patches which probably consist of clay or 

 kaolin. 



b,— Slates. 



By the addition of a gradually increasing proportion of micaceous 



minerals to these fine-grained sandstones, we obtain the rocks 



that constitute the greatest part of the Bijawar slates to which 



class belongs the specimen /^ which has just been mentioned. 



Slates of a deep purple colour are very frequent 



Purple slates; re- 

 semblance to the Red especially in the horizon where jasper bands and 

 Shales. . 



lava-flows are most numerous. These purple 

 slates completely resemble the red shales. The only difference that 

 can be made out is a slight difference in colour. The red shales are 

 of a more decided purple colour, while the similar Bijawar 

 shales are somewhat tinted with a shade of steel blue. The difference 

 is a slight one, but it is quite distinct when specimens of the two 

 rocks are brought close together. It is not possible to make out the 

 exact nature of the pigment as it is extremely fine-grained and quite 

 opaque. It is no doubt of a ferruginous nature and this causes the 

 high specific gravity of these rocks. The microscopic sections are 

 rendered opaque to a great extent by this ferruginous material, which 

 lies between the other minerals spread along the direction of 

 cleavage. Besides this ferruginous material, there are small grains of 

 quartz and flakes of mica, the latter mineral being the more abundant 

 of the two. It occurs in greatly crumpled bundles polarising in 

 high colours. 



' ( 64 ) 



