Federated Malay States. 457 



rock contains light-brown augite with lamellar twinning. Apatite is 

 a very constant accessory and is often very abundant. 



The most common secondary minerals are calcite derived in part 

 from neighbouring sedimentary rocks and epidote. Some of the 

 calcite is an alteration-product of the felspar. A dark-green fibrous 

 mica has been noticed occasionally. The groundmass is usually 

 a holocrystalline fine-grained granitic mosaic of quartz and felspar in 

 which sometimes microlites of felspar can be detected, and occasionally 

 a microspherulitic structure is present, while some quartz-porphyries 

 have a granophyric groundmass, and thus form a link with the 

 granophyres next to be described. 



Geanophyre. 



The granophyres are exposed in the Pahang River for a distance 

 of 2 miles upstream from Pulau Guai, 2 or 3 miles above 111th mile 

 on the railway, and with the quartz-porphyries of the 101st mile on 

 the railway. The exposures in rive,r and railway all occur on a line 

 of strike running about JN\ 10° W. by S. 10° E., and the intrusion 

 may be quite narrow, but if continuous its length is over 10 miles. 



It is usually white in colour, and all the specimens that have been 

 collected have a specific gravity of about 2-60. Under the microscope, 

 particularly between crossed nicols, these rocks present a beautiful 

 appearance. Uuartz phenocrysts and phenocrysts of orthoclase and 

 oligoclase make up a large portion of the rock. Biotite mica is 

 sometimes present, and apatite and pyrites are constant accessories. 

 Of secondary minerals calcite is the most common, and one specimen 

 has felspar phenocrysts containing abundant flakes of chlorite. 



A lava with traces of granophyric structure occurs just below 

 the mouth of the Paver Chika, interstratified with Gondwana rocks, 

 but near the boundary of the outcrop. It may be of the same period 

 of eruption as the granophyre intrusions, which would therefore 

 be assigned to the period of deposition of the oldest Gondwana rocks, 

 but the fact that tuffs which are interstratified with Raub rocks 

 contain granophyre fragments shows that the period of intrusion of 

 some of the granophyre was Raub. 



Reference has already been made to the boulders of dark-coloured 

 quartz-porphyry which lie scattered about on the [Main Granite 

 Range. They occur at the Ginting Sempak* road at the 11£, 

 17th, 20£, 22£ miles, and at several places going down the Pahang 

 side of the pass, also on the way to Ginting Bidei* from Ivlang 

 Gate*, both as boulders and in situ, and as a single boulder near the 

 8th mile Rawang road*. 



In the hand-specimen white phenocrysts of felspar and quartz can 

 readily be distinguished, the dark-purple or black groundmass having 

 a compact homogeneous appearance, and under the microscope it is 

 seen that the felspar varies from oligoclase to labradorite and that it 

 is often strongly zoned, the kernel being more basic than the exterior 

 zones. The felspar and quartz are angular in outline and sometimes 

 rounded. A little uralitized augite is an occasional constituent, 

 suggesting a connexion with the granite-porphyry next to be 

 described. Well-shaped crystals of biotite are common, often very 



