PETROGRAPHICAL NOTES. 87 



represent drawn-out cavities subsequently infilled by the mineral, so 

 that the rock may have been originally a scoriaceous basalt. As to 

 the small chlorite masses, if they were also filled up cavities, we 

 would expect to see them assume the same shape as the larger ones 

 filled with calcite, instead of which their dimensions are only very 

 slightly greater along the direction of bedding. They are perhaps 

 pseudomorphs after some porphyritic constituents whose crystals 

 were arranged along the direction of flow. Under the microscope 

 the fine groundmass of the rock is quite similar to that described in 

 the case of the Jabalpur rock f|. It consists of hornblende, felspar, 

 leucoxene and chlorite. The hornblende is in minute prisms and 

 fibres frequently curved. The felspars give wavy extinction, and 

 their mass is penetrated into by chlorite and minute hornblende needles 

 that entirely obscure their crystalline outline. Leucoxene occurs 

 in large quantity forming streaks and patches all over the section. 

 The chlorite masses appear under the microscope as spherical or 

 ovoid aggregate of felted chlorite scales associated with epidote and 

 calcite. The secondary growth of the minerals surrounding these 

 patches has generally obscured the shape of the original porphyritic 

 mineral whose place they occupy. In a few cases the shape may 

 still be partly recognised, and it would seem that the original 

 mineral was olivine. The rock would then be very similar to the 

 one next to be examined. 



This is a very fine-grained melaphyre with porphyritic augite 

 and olivine, collected at Jarkarua in the river 



Altered olivine-basalt. 



bed immediately north of the Red Shale bound- 

 ary (specimen T VV)* The P°int 3 (Fig. 6) is in the direct continuation 

 of its strike. It occurs therefore at a short distance from the band 

 containing the diabase -f-^ which we found to contain unaltered 



augite (page 82), and this remarkable feature 



Unaltered augite. ... 



is again exhibited in the melaphyre T y T , showing 

 that this must be a region of lesser metamorphism amongst the 

 Bijawars. It resembles a basalt in the hand-specimen with, 

 however,, a greenish tinge, and is mottled all over with dark green 



( 8 7 ) 



