104 GEOLOGY OF THE SON VALLEY, ETC. 



day's work brought me to the little hills close to Nubbeenuggur. I 

 expected to find quartzite such as protrudes from the alluvium to the 

 East and which shows again at Jupla to the West. It proved, how- 

 ever, to be a massive rock closely akin if not identical with the trap- 

 poid variety of Kalapahar, and intimately associated with sharply 

 bedded Sone rocks of the felspathic type ; the coarse trap ( poid rock 

 shows massively in two small bosses near the end of the low ridge on 

 the South ; the sharply bedded rocks of the ridge have a low undulat- 

 ing dip to North-North-West ; among them are thicker beds of coarser 

 variety and showing evident affinities to the massive rock, which I 

 suspect only the outcrop of a very thick bed.' 1 It is possible that the 

 thick bed to the south is a real lava-flow, while those interbedded 

 with the porcellanites might be tuffs. But the connection between the 

 two is beyond doubt. Originally the rocks were represented in the 

 collection by two specimens, T ^ described as u coarse variety of trap- 

 poid from Nubbeenuggur," and y^ labelled "ditto"; is seen well in- 

 terstratified with finely- bedded rocks, S. of Kokha. Presumably y^ 

 is the rock from the more massive exposure. It is unfortunate that 

 the specimen T ^ has been lost, as it would have been otherwise inter- 

 esting to compare the two, but T -g-^ is a typical lava. It has in the 

 hand-specimen the appearance of a coarsely porphyritic rhyolite. 

 The matrix is partly pale-coloured and resembling that of the ordin- 

 ary " trappoids," while elsewhere irregular veins or branches of 

 black obsidian run through it, containing large porphyritic felspars as 

 much as one centimetre in diameter and porphyritic quartz. 



Under the microscope the rock is seen to consist of idiomorphic 

 or fragmentary crystals of quartz, orthoclase, and plagioclase, show- 

 ing the usual phenomena of corrosion, principally in the case of the 

 quartz. The groundmass is crypto-crystalline and shows conspi- 

 cuous flow-structure. Both the crystals and groundmass are identi- 

 cal in character with the fragments constituting the " trappoids " 

 and " porcellanites." 



We may now safely conclude that the region between Kutumbeh 

 „ , . , and Japla is in the neighbourhood of one of the 



Volcanic focus. . . 



principal foci of activity of the Vindhyan period. 

 ( 104 ) 



