The Rods of Pulau Ubin and Pulau Nanus. 055 



of considerable interest. Pulau Ubin is composed mainly of horn- 

 blende-granite, but a pyroxene-bearing microgranite is found also; 

 while the hornblende-granite is cut by rhombic-pyroxene bearing 

 veins and also contains angular masses of rock resembling the veins. 

 The following grouping of the Pulau Ubin rocks (with which is 

 included a rock found in the granite of Changi) is adopted. 



. (L) 

 Normal hornblende-granite with a little monoclinic pyroxene. 



(II.) 

 Pyroxene-microgranite with dark masses resembling III (i). 



(III.) 

 (i) Porphyry, with peculiar spongy masses of hornblende, 

 (li) Masse8 of a rock at Changi having the mineral constitution of an 

 ampbibole-vogesite. 



(IV.) 

 (i) Veins of quartz-norite in the normal granite, 

 (ii) Veins and masses of enstatite-spessartite in the normal granite, 

 (iii) Masses of quartz-biotite-gabbro in the normal granite. 



Pulau Nanas consists of dacite-tuffs and dacite which are 

 referred to the Pahang Volcanic Series, of Carboniferous or Permo- 

 Carboniferous age. The tuffs and lavas have been altered by the 

 adjacent granite of Pulau Ubin, and contain much secondary 

 biotite and hornblende. They also contain some fragments that 

 appear to be altered chert, but their most remarkable feature is the 

 presence of fragments of altered granite. 



The author discusses the mutual relations of the different rocks, 

 and arrives at the following conclusions : — 



(1) The normal granite of Pulau Ubin is hornblende-granite, 

 the age of which is certainly post-Triassic and prc-Eocene, perhaps 

 post-In ferior-Ooli to and pre-Cretaceous. 



(2) Veins of quartz-norite and masses of <]iiartz-biotite-gabbro, 

 and veins and masses of a fine-grained rock which may be described 

 as enstatite-spessartite, are found in the normal granite of Pulau 

 Ubin. These point to an early differentiation of a granite and a 

 gabbroid magma, perhaps in pre-Cretaceous times, and they are 

 referable to rocks in Borneo and Amboyna. 



(3) A pyroxene-microgranite and porphyry on Pulau Ubin, and 

 a rock at Changi, having the mineral constitution of an amphibole- 

 vogesite, are described. Their relations to the other rocks are 

 not clear. 



(4) The dacite-tuffs of Pulau Nanas contain fragments of granite 

 which must he of pre-Carboniferous age, and are referable to the 

 granite of Amboyna. 



(5) The fragments of granite, and perhaps certain pebbles of 

 schorl-reck, are the only evidence found as yet in the Malay 

 Peninsula of pre-Carboniferous rocks. 



4. ' The Tourmaline-Corundum Pocks of Kinta (Federated Malay 

 States).' By John Brooke Scrivenor, M.A., P.G.S. 



Overlying the limestone on the west side of the Kinta Vallev is 



