Yol. 56.] THE GEOLOGY OF GILGIT. 367 



other. Kesolution seems to me to follow a similar course. Where- 

 ever a point of weakness presents itself, the corroding liquid begins 

 its inroad. Occasionally residual quartz may be seen actually 

 passing into granophyre : an illustration of one such case is shown 

 in PI. XXIII, fig. 6. 



The causes which led to the formation of the quartz-mosaic 

 so frequently seen in the Himalayan granites were discussed in some 

 detail in my paper already quoted, and need not be repeated. These 

 mosaic structures are equally abundant in the Gilgit granites, and a 

 similar explanation applies to them. Briefly stated, it is that the 

 large quartz-crystals and the felspar suffered partial resolution 

 during the movement of the granite into place, and were penetrated 

 by intrusive veins of liquid quartz. The tessellated structure, ac- 

 cording to my view, was imposed on this residual quartz by strain 

 at the moment of its final crystallization. The larger quartz- and 

 felspar-crystals do not exhibit this structure. The quartz-mosaic 

 is not an uniform granular structure pervading the whole rock, but 

 appears in the quartz and felspar more like a granite invading a 

 sedimentary rock. 



The structures seen in the shattered and sheared granites of the 

 Gilgit area are quite different in character. In them the quartz 

 and felspar are sheared down into strips. 



An interesting question suggested by the study of the Gilgit rocks 

 is whether the intrusion of the granites described took place 

 before, during, or after the crumpling of the sedimentary rocks ? 

 The full elucidation of this problem must be left to future observers. 

 The intrusion of the granites evidently occurred during a very ex- 

 tended period, measured in years, and I am disposed to think, from 

 the facts presented in this paper, that the eruption of the Baltit 

 Hornblende-Granite began when the crumpling of the strata was in 

 progress. It is clear that the eruption of part of the Hatu 

 Pir Granite, at all events, must have taken place after the mono- 

 clinal folding had been completed, for it cuts obliquely across the 

 limestone-beds (see p. 354). Had these beds been folded, or 

 compressed sufficiently to cause a differential movement of the beds 

 which were in contact, after the intrusion of the granite, the 

 oblique dykes must have been faulted and dislocated. The plication 

 of horizontal beds into a series of folds, and the compression of 

 these folds into monoclinal strata, must have produced a differential 

 movement, or shearing, between the beds that were in contact one 

 with the other, and this movement must inevitably have left its 

 marks on the oblique dykes of granite intruded into the limestones 

 before the movement ceased. 



It follows also, if the foregoing conclusion be admitted, that the 

 acid variety of the Hatu Pir Granite and the Askurdas Granite 

 were also intruded after the crumpling of the strata had been 

 completed, for they are both younger than, and are intruders in, 

 the Hatu Pir Granite. This conclusion has an important bearing 

 on the age of these granites. 



2c2 



