214 Col. McMahon — Granite of the Himalayas. 



never coarse-grained), but occasionally it becomes so extremely fine- 

 grained that the rock assumes, to the unaided eye, the appearance of 

 a felspar porphyry. In the perfectly granitic varieties the porphyritic 

 crystals of felspar, which sometimes attain a length of from three 

 to three and a half inches, orient in all directions, and present 

 sharply rectangular forms. From the porphyritic-granitic and non- 

 porphyritic-granitic varieties the rock passes by gradual transitions 

 into a more or less foliated granite. The passage from one variety 

 to the other is often apparently capricious ; but even in the most 

 perfect granitic masses a tendency towards foliation may generally 

 be observed at its edges. 



Speaking generally, the granite of the inner outcrop is foliated 

 along both margins; and the foliation becomes intense where the 

 band contracts, on the north side of the river Ravi, to a width of 

 two hundred and fifty feet. At this point it passes, on its western 

 margin, into what, from its macroscopic aspect, would be called a 

 mica-schist. 



The outer band of gneissose-granite is intensely foliated. It does 

 not indeed pass into a mica-schist ; but it not unfrequently looks, 

 viewed macroscopically, as if it had been flattened under a steam 

 roller. 



Joints are abundant ; and they frequently simulate bedding ; but 

 true bedding is not to be seen. 



The granite is composed of orthoclase, plagioclase, microcline, 

 quartz, biotite, and muscovite. In some localities biotite pre- 

 dominates — in others muscovite. Magnetite, garnets, and apatite are 

 sometimes present ; whilst schorl is rarely absent from the granitic 

 varieties. The presence of ilmenite may also be inferred from the 

 occasional existence of leucoxene. 



Mircoscopic characters of the Gfieissose- Granite. 



Under the microscope the granite yields abundant evidence of 

 strain, pressure, and shear or traction. The twinning planes of the 

 triclinic felspars are sometimes bent ; felspars are frequently cracked, 

 fractured, and occasionally the pieces are pushed over like books on 

 a shelf; whilst crumpled micas may be seen which have been com- 

 pletely bent and one end folded over on the other like a sheet of 

 note-paper preparatory to being placed in an envelope. 



A prominent characteristic of every variety of the Dalhousie 

 gneissose-granite, even the most granitic, is the presence of what I 

 have called in my papers by the short term of crypto-crystalline 

 mica. • It is mostly a form of muscovite, though the imperfectly 

 crystallized material of biotite is occasionally present in ropy masses. 

 This crypto-crystalline mica varies from a pale-buff to a pale-grey 

 colour, and it has a superficial resemblance to the base of some 

 felsites and rhyolites. In its typical form, though its double refraction 

 is strong, no definite crystals of mica can be made out ; and the 

 leaflets, under polarized light, melt into each other and exhibit no 

 definite shape. This crypto-crystalline mica passes into a niioro- 

 crystalline condition, in which the leaflets, though of extreme micro* 



