LOWER VINDHYAN SERIES. 103 



Aliuneggur, just as at Kalapahar." Here again microscopic examin- 

 ation shows it to be not a derivative rock, but an igneous rock similar 

 to those already described. Under the microscope it resembles best 

 the more perfectly crystalline rock T J ¥ . It consists of porphyritic and 

 idiomorphic plagioclases, biotites, and hornblendes, in a microgranitic 

 and micrographic groundmass of quartz and felspar very similar to that 

 of yi-g- only on a much smaller scale; it is therefore somewhat inter- 

 mediate in character between T J ? and T J ¥ . Although the two rocks 

 y| 7 and y^ do not possess any large porphyritic crystals of quartz 

 like in the case of 1 ^ 7 , yet that mineral is present in such abundance 

 in the base that it probably exists in the same proportion in all three 

 specimens. Considering that the two more highly crystalline varieties 

 must have taken longer to solidify, it might be suggested that 

 the absence of porphyritic quartz is due to its complete solution by 

 the magma, for the crystals are already corroded to a great extent 

 in the less perfectly crystalline rock y^ whose magma must have 

 solidified more rapidly. 



The accounts given of the manner in which all these rocks occur 

 certainly give the impression that though they are not true beds of 

 lava, they are probably intrusive sheets. In any case they are vastly 

 newer than the more intense phase of foliation of the region, for 

 these signs of dynamic-metamorphism so conspicuous in the granitic 

 gneiss are absent from the overlying felsites, or only very weakly 

 exhibited, and belong to the same order of disturbance as that 

 generally seen in the Vindhyans. The complete similarity of their 

 minerals with those of the Vindhyan tuffs makes it very probable 

 that they are genetically related, and we have here, in fact, one of 

 the volcanic foci from which these rocks were derived in such abund- 

 ance. 



Finally there is one more exposure where the connection of these 

 „ ' _ , rocks with the ordinary stratified porcellanites 



Rocks collected by ..... 



Mr. Mediicottat Nabi- is beyond doubt, It is in this same neighbour- 

 oagar - hood, at Nabinagar {Lat. 24 36', Long. 84 



11'). Mr. Medlicott describes it in the following terms : " My next 



( 103 ) 



