PETROGRAPHICAL NOTES. 75 



gradation does exist, and that if the region were surveyed with 

 that object a series of complete gradations could be obtained. 



The first stage of alteration that has been observed is illustrated 

 by the specimen -fa collected in Bundelkhand 

 ^aU^sm!' f "> m * hill north-west of the road from 



Chowkee to Dergrah. It is coarser-grained 

 than the two rocks just described. It resembles them in the 

 hand-specimen, but it already shows a faint greenish tinge. Its 

 specific gravity is 2*97. It consists of the same minerals, but 

 one of them at least is distinctly altered : this is the augite which 

 shows initial stages of uralitisation. It was originally a brown 

 augite similar to that of the unaltered dolerites, but much of it 

 is now coloured green in irregular patches caused by numerous 

 particles of hornblende disseminated throughout its mass, and in 

 a few places the transformation is complete. Where the mineral 

 has not been changed to hornblende it is striated and clouded 

 and stained with ferruginous products. The felspar is altered 

 in the micropegmatitic intergrowths and sometimes in patches 

 through the crystals, but on the whole it is as fresh and unaltered 

 as in many much more recent rocks. The ilmenite shows no signs 

 of any change. 



Metamorphism has proceeded to a far greater extent in the 

 specimen f. It is interesting as being derived from the same 

 locality as the unaltered dolerites § and ^, showing that rocks in 

 distinctly different stages of metamorphism occur at no great 

 distances from one another. In the hand-specimen this rock has 

 a decided resemblance to some of the Son region specimens poorer 

 in chlorite. Its colour is already such as to justify the name of 

 11 greenstone." The rock is finer-grained than those last de- 

 scribed. The proportion of hornblende is much greater, and some of 

 jt occurs in fibrous forms. Chlorite makes its appearance. Yet there 

 is still a great deal of augite; but the alteration of the felspars has 

 proceeded to a considerable extent. 



Next to this rock we may class ff f a contemporaneous lava 



( 75 ) 



