V. NOTE ON A COLLECTION OF ROCK 



SPECIMENS FROM PULAU PISANG, WEST COAST 



OF JOHORE. 



By J. B. Sckivenor, Geologist, F.M.S. 



In May igi6 Mr. C. Boden Kloss sent me a collection of 

 rock specimens from the small island, Pulau Pisang, off the 

 southern part of the west coast of Johore. Mr. Kloss stated 

 that only two of the specimens represent rock that he saw 

 exposed in situ and that the remainder came from a shingle 

 beach. All the specimens are from the north side of the 

 island. 



These specimens are of sufficient interest to warrant a note 

 on them and their relations to other rocks in the Malay 

 Peninsula. On glancing over the collection one had the 

 impression that they were largely rocks of the " Chert Series" 

 indurated by metamorphism, and thin sections prepared for 

 the microscope support this view, while a pebble of granite in 

 the collection shows how the metamorphism was effected, but 

 on the other hand they show that volcanic ashes are also 

 represented on the island. The following is a brief description 

 of the rocks. 



i. Granite. This pebble is too small to say what type of 

 granite it was derived from. The slide contains only one mica, 

 biotite, but a larger specimen might very likely show muscovite 

 as well. There is nothing unusual about the rock. 



2.. Qua/rtz-mica-syenite-porphyry. Nothing exactly corres- 

 ponding to this rock has been found before in the Peninsula 

 and it is unfortunate that it is only represented by a pebble. 

 Hornblende is common and there is an equal quantity of 

 altered biotite also in fairly large flakes. There are numerous 

 porphyntic crystals of felspar full of finely divided decom- 

 position products. Some of them appear to be kaolinized 

 orthoclase but others show traces of polysthenic twinning. 

 The felspar crystals are generally bordered by a very delicate 

 growth which in some cases looks like a radial arrangement of 

 minute fibres of felspar, but with a high power much of it is 

 resolved into a micropegmatitic intergrowth of quartz and 

 felspar. Quartz is confined to this intergrowth and to the 

 base, which does not form a large proportion of the rock and is 

 of felspai and quartz in small grains. The quartz is a minor 

 constituent, and the rock is a porphyry of same composition 

 as quartz-mica-syenite. The nearest approach to this rock 

 known as yet in the Peninsula are certain svenitic rocks found 

 in the Benom Range of Pahang (vide "The Geology and 

 August, 1916, 



