PETHOGRAPHICAL NOTES. S7 



^nd often very beautiful in appearance. In some, as for instance 

 No. 1 1 '578, the sphaerulites are isolated globules, scattered about in the 

 body of the rock and giving a dark interference cross between crossed 

 Nicols. In others, the different individuals forming the "quartz 

 mosaic " each contain in their interior a radiating bunch of minute 

 crystals, so that between crossed Nicols a number of little black crosses 

 make their appearance revolving as the Nicols are rotated like so many 

 minute wheels. In these cases the mineral forming the radiating 

 aggregates is felspar. In some others again minute needles of horn- 

 blende are intercalated among the felspar crystals, giving rise to the 

 beautiful sphaerulites seen in No. 1 I363 (PI. XI, fig. 3). In this speci- 

 men, where the sphaerulites abut against a quartz phenocryst, the quartz 

 filling the interstices between the hornblende and felspar needles is, for 

 -a short distance from the edge of the phenocryst, in optical continuity 

 with it. A sphaerulitic structure of this kind also occurs along the 

 •edges of the more coarsely crystalline bands in those rocks that possess 

 flow-structure (PL X, figs. 3, 4), and in the latter specimen perfect glob- 

 ular sphaerulites occur in the middle of the broader bands. The large 

 sphaerulites in the specimen No. 1 1-523, described in the last paragraph, 

 • are often broken across, and fragments of them lie scattered about in all 

 directions in the body of the rock. In this rock they generally have a 

 quartz grain at the centre. 



Among the specimens collected in the Boulder bed of the Salt Range 

 by Mr. Middlemiss and described by him in the Records of the Geo- 

 logical Survey • there is one which corresponds very closely in appear- 

 ance with some of the rhyolites of Western Rajputana. This is 

 No. 8-473, which is almost identical with No. 11 5 12 from my collec- 

 tions from the group of hills near Agolai. The variable structure of 

 the groundmass, which is strongly fluidal, described by Mr. Middlemiss 

 is exactly repeated in my specimen, and the boulder from the Salt 

 Range might have been broken off a portion of the same flow. It is 



1 Rec. Geol. Surv. Ind., Vol. XXV, Pt. 1, p. 29. 



e ( 8 ? ) 



