PETROGRAPHICAL NOTES. 73 



occurs between two runs of jasper, it forms an area of lower ground, 

 as in the longitudinal valley of Piperwani. But if these same rocks 

 are bounded on one side by nothing but the softer slates, then they 

 themselves rise into ranges comparable in height with those formed 

 by the jaspers, as in the case of the range which contains Belawa 

 peak. 



b.— Petrography. 



All these rocks may be divided into two classes; those that 

 are properly speaking igneous, and others which 

 Classificat.on. p arta ke of a sedimentary character and pro- 



bably of a tuftaceous nature. 



The rocks of the first class are principally uralite-diabases, and 

 altered basalts or melaphyres. Some of them are somewhat coarse- 

 grained like one of the specimens from Bhanni (-g^) described by 

 Mr. Oldham as obtained from a dyke; and we get every gradation 

 up to rocks which originally must have contained a large proportion 

 of glassy magma, such as jW from Dholki. All the volcanic rocks 

 from the Son outcrop of the Bijawars are, w ithout 



Metamorphism. . . 



exception, altered to a considerable extent. 

 Unaltered olivine has not been observed. Augite was found in two 

 instances only ( T y^ and 7 y T ) and is then of th£ pale-coloured variety, 

 poor in iron. In every other instance it is entirely altered to an 

 extremely pleochroic uralite, while at other times, especially in 

 the base of some of the finer-grained rocks, it appears to have united 

 with part of the substance of the felspars to form needles of paler 

 hornblende. The felspar is universally saussuritised to a considerable 

 extent. Ilmenite has often entirely changed to leucoxene. The 

 secondary hornblende itself is often further altered to chlorite and 

 epidote. In fact epidote and chlorite are abundantly developed in 

 all these rocks ; chlorite is never absent and contributes more than 

 any other mineral in communicating to them their characteristic 

 green colouration. 



( 73 ) 



