Federated Malay States. 459 



crystals in the quartz-porphyry last described, but some of it is not 

 distorted in any way, and from this, and the very irregular outline, 

 it is concluded that some of the biotite is secondary. 



The pyroxene is in colourless, poorly shaped crystals, and much 

 of it is certainly a monoclinic variety, but some crystals showing 

 longitudinal cleavage extinguish straight between crossed nicols and 

 are therefore a rhombic pyroxene. The interference colours in slides 

 where quartz sometimes gives pale yellows vary between wide 

 limits, for both the monoclinic and the rhombic pyroxene, from grey 

 of the first order (like quartz) to brilliant blues and greens of the 

 first order. The pyroxenes are altered to two distinct products, one 

 appearing in section as a thin strip surrounding the crystals, made 

 up of small fibres of green mica, set diametrically across the strip, 

 and thin bands having this composition sometimes penetrate the 

 augite and the quartz and felspar too. The other alteration-product 

 is a pale-brown chlorite of mica in plates and flakes which replace 

 the greater part of the crystal. In some specimens some of the 

 pyroxene crystals have been completely replaced by the alteration- 

 product, while in others the pyroxene is left quite fresh. 



Erom the specimens examined it appears that since consolidation 

 the rock has been affected by considerable earth movement resulting 

 in a complete reconstitution of the groundmass, the partial brecciation 

 of the crystals, and the formation of biotite. 



It is probable that a trip further upstream beyond Jeram Gading* 

 will show this granite-porphyry in situ, for boulders of pebbles of 

 the rock are very common there. From the description of the rock 

 it is clearly a metamorphosed igneous rock — the granulitic ground- 

 mass, the brecciation of the crystals, the puckering of the original 

 altered biotite, and the interstitial nature of the other rich brown 

 biotite all indicate that it has been formed from an igneous rock by 

 intense shearing movements. Although many of the boulders of the 

 rock in the River Seli * and on the flanks of the Ginting Bidei * hill 

 are many yards across, yet no exposures clearly in situ were seen. 



Occasionally small patches of a finer-grained material are enclosed 

 in the rock, which when examined under the microscope are found 

 to differ from the rest of the granite-porphyry only in their finer 

 grain. Apart from these few patches, the rock is remarkably constant 

 in grain as -well as in composition, and considering that it is known 

 to occur intermittently as large boulders over an area of 100 square 

 miles this is perhaps one of its most striking features. 



Boulders of schist, made up of hornblende, augite, and felspar, 

 were collected from the same locality, and one less metamorphosed 

 specimen contains altered fragments which reveal that the original 

 rock, from which the schist was formed, was a porphyritic igneous 

 rock. The three minerals are confined more or less to individual 

 bands, with a thickness sometimes reaching J inch. The hornblende 

 is a green pleochroic fibrous variety, and the augite is light-brown 

 in colour, occurring like the felspar in granules. The felspar is 

 orthoclase. The specimen mentioned above, which has been less 

 highly metamorphosed, does not show a foliated structure. It is 

 made up of sheared oligoclase-andesine felspars set in a fine-grained 



