PETROGRAPHICAL NOTES. 63 



The specimen j^ is a very fine quartzite collected from a 

 point west of Chatni and north of one of 



Chatni. r , 



the most important outcrops of lava. In the 

 hand-specimen it is a compact pale-grey rock of fresh ap- 

 pearance but with distinct cleavage. Under the microscope it 

 appears composed of very small sand-grains with much interven- 

 ing micaceous mineral. The sand-grains are mostly quartz exhibit- 

 ing strain-shadows to a marked extent. Scattered through them 

 are a few grains of felspar. The micaceous minerals are white 

 mica, very much altered, and some secondary chlorite. 



This fine sandstone grades imperceptibly into slates such as 



specimen y 1 ^. In the hand -specimen it is a com- 



Finer-grained rocks. 



pact light-grey slate with very regular cleavage. 

 Under the microscope it is seen to consist essentially of the same 

 minerals as j^, quartz and mica, only it is extremely fine-grained and 

 the proportion of mica is much greater. The quartz-grains have their 

 longer dimension lying in the direction of the cleavage. Whenever 

 the principal section of one of the crossed Nicols is parallel 

 to the cleavage, the section extinguishes entirely with the excep- 

 tion of the quartz-grains, thus showing the perfect parallelism of 

 all the micaceous constituents which give the rock its regular 

 cleavage. The micaceous mineral consists largely of white micai 

 muscovite or sericite polarising in brilliant colours. There is in 

 addition a fair proportion of chlorite. 



The rock T \^- is so fine-grained that it should be classed as a 

 slate, the component grains being quite invis- 



yuartz-slate. . 01 



ible without the aid of a lens. But as the 

 microscope shows it to consist almost entirely of derived fragments 

 of quartz, it is properly grouped with the foregoing sandstones. It 

 is in fact a sandstone on a microscopic scale ; the quartz parti- 

 cles have none of the appearance of secondary crystallisation 

 as is the case with the jaspers. The specimens were collected 



Chakari * n the riV6r that flows throu & n Chakari a short 



way west of the Vindhyan boundary. The 



( 63 ) 



