18 



J. B. Scrivenor — Igneous Rocks of Singapore. 



been seen in situ. They are the only evidence at present of pre- 

 Triassic rocks in the island. Close to the Ballestier lload, and not 

 far from the junction with the Thomson Road, small boulders were 

 found exposed on the site for a hospital. These consist of trachyte. 

 At the corner of Grange and Orchard Roads small boulders of 

 andesitic tuffs were found, similar to the tuffs in' Pahang. 



JO more: 



Yiii. 1. — Sketi'h-m:ip showing I'Lihui Ubiu and Changi, vSiiigapure. 



Roclis of Bouhtful Position : Quartz Porpliyry. — At Pulau Pergam, 

 in the Straits of Johore, is a mass of ' core-boulders ', i.e. hai'd 

 unweathered cores left from the denudation of a bed or mass which 

 once occupied approximately the same site, lying on the same rock in 

 situ. It consists of blebs of quartz and crystals of orthoclase, with 

 some of plagioclase and microperthite, crowded together in a green 

 chloritic base. A little biotite occurs, and in one slide flow-structure 

 was seen. This quartz porphyry may belong to the same period of 

 eruption as certain masses of quartz porphyry in the Federated 

 Malay States connected with the granite, or it may be referred to 

 certain masses of quartz porphyry that occur isolated from other 

 igneous rocks. The data are too few to speak with anything 

 approaching certainty. 



Ophitic Dolerite or Diabase. — On the hospital site near the 

 Ballestier Road the writer found two boulders of an altered ophitic 

 rock with pale-green secondarj- amphibole, epidote, and masses of 

 minute flakes of biotite. The rock recalls certain diabases in the 



