J. B. Scriienor — Igneous Rocks of Singapore. 19 



peninsula ; but, like them, cannot yet be assigned to anj particular 

 group. At the corner of Grange and Orchard Roads again, bouldera 

 of a less altered ophitic rock were found containing violet augite, 

 olivine, calcite, and plagioclase. Dolerite dykes are known to traverse 

 the granite in the Peninsula ; therefore it is quite probable that these 

 boulders were derived from similar dykes in Singapore. On the other 

 hand, they may be remnants of basic lavas of the Pahang Volcanic 

 Series. 



The Granite. — In the Federated Malay States granite immediately 

 suggests the possibility of the occurrence of tin-ore, and it would 

 appear that at one time tin-ore was worked in Singapore, because the 

 name " Bukit Timah ", which is given to a granite hill in the interior 

 of the island, signifies the " Tin Hill". The writer is not aware of 

 any records of tin-working there, however, and no traces of cassiterite, 

 or indeed of any of the granite modifications which may generally be 

 taken as guide to tin deposits, were discovered. But at Bukit 

 Panjang, farther to the north, the writer found a small pocket of 

 cassiterite, molybdenite, chlorite, and calcite in the granite. The 

 weight of the cassiterite is considerably under a gram ; therefore the 

 first recorded occurrence of tin-ore in Singapore cannot be said to be 

 encouraging from a commercial point of view. The noi'mal granite is 

 a medium-grained, non-porphyritic rock, with biotite and varying 

 amounts of green hornblende. Sometimes the biotite occurs alone. 

 A considerable proportion of the felspar is plagioclase. 



At Bukit Timah the granite contains comparatively little biotite, 

 and was found in one place to pass into a rock consisting of crystals 

 of orthoclase, and quartz generally showing crystal outline, together 

 with a biotite, in a ground-mass of even-grained mosaic of quartz and 

 felspar. 



At Changi the grauite contains more hornblende than biotite, and 

 in this hornblende-granite was found a vein of rock strongly 

 resembling, in a hand-specimen, a tourmaline bearing modification of 

 granite. Under the microscope, however, it proved to consist of 

 quartz grains and poorly formed crystals of orthoclase, with irregular 

 masses of dark-green hornblende. 



On Pulau TJbin the normal type of granite is predominant. It is 

 worked in large quarries along the coast of the island. The most 

 interesting specimens collected on Pulau Ubin, however, are certain 

 pyroxene-bearing rocks which require more detailed description. 

 They were found in the Municipality Quarry on the north of the 

 island. 



Slides from a piece of the ordinary granite in this quarry do not 

 show anything of particular interest. The proportion of ferromagnesian 

 minerals (biotite and hornblende) and iron-ores is not large. One 

 specimen {a) was collected, however, that is much darker than this 

 granite. In the hand-specimen the felspar appears fresh, and the 

 quartz cannot be distinguished with certainty. Biotite is plainly 

 visible. Sections show that quartz is not very abundant, and that 

 there is more plagioclase than orthoclase. The ferromagnesian 

 minerals are biotite, fibrous amphibole, and rhombic pyroxene. The 

 three are as a rule closely associated, and there is good reason to 



