﻿422 THE ROCKS OF PULAU UBIN AND PULAU NANAS. [Aug. I9IO, 



II. PuLAU TJbLN. 



The Normal Granite. 



The normal granite of Pulau Ubin is a medium-grained horn- 

 blende-granite. The proportion of ferromagnesian minerals (green 

 hornblende and biotite) varies. Apatite, zircon, and magnetite are 

 common. The felspars are orthoclase and a soda-plagioclase. In 

 some slides the latter is abundant, in others scarce. There is 

 nothing remarkable about the quart/. 



Large quantities of the heavier minerals in this granite have been 

 concentrated with a view to searching for pyroxene, good material 

 for this purpose being found at Tanjong Jelutong, near Quarries 2 

 & 3. Monoclinic pyroxene was found in small quantities, but no 

 rhombic pyroxene, except in one case (in the North Quarry) where 

 the rock was so near rocks bearing rhombic pyroxene that the 

 evidence was not conclusive. In the North Quarry two very small 

 veins were found traversing the normal granite, one consisting of 

 dark-green monoclinic pyroxene, hornblende, and garnet, the other 

 containing wollastonite and garnet. 



Microgranite with Monoclinic Pyroxene. 



This occurs in the South Quarry : it is fine-grained and very 

 pale. In section the dark minerals are seen to be granules of 

 green monoclinic pyroxene, hornblende, biotite, sphene, and abundant 

 magnetite. For the rest, the rock is composed of a rough mosaic 

 of quartz, orthoclase, and soda-plagioclase, the last being common. 



A small vein in this rock was found to consist of quartz, ortho- 

 clase, soda-plagioclase, sphene, and abundant monoclinic pyroxene. 

 This vein was probably formed by segregation. 



The microgranite occupies most of the South Quarry, but at one 

 end (the far end from the landing-place) normal hornblende-granite 

 was found. Its relation to the microgranite was not clear. 



There are a few dark patches in the microgranite that will be 

 described later. 



Rocks bearing Rhombic Pyroxene in the North Quarry. 



In my previous paper I mentioned three rocks from the Munici- 

 pality, or North Quarry, which were designated by the letters a, h, 

 & c. 1 On revisiting this quarry I found that work on the face 

 had progressed greatly and that a very interesting section had been 

 exposed : this is reproduced diagrammatically in fig. 2 (p. 423). 

 No doubt exists now as to the relation of the rock a to the granite, 

 as may be gathered from the following description of the section, 

 based on a large number of slides cut from specimens collected from 

 different parts of the face. 



1 Geol. Mag. dec. v, vol. vi (1909) pp. 19-21. 



