﻿Yol. 66J] PtTLAtT T7BIN AND PTJLATT NANAS. 425 



In my previous paper I mentioned a small vein of pink garnet, 

 pale-green monoclinic pyroxene, wollastonite (largely altered to 

 calcite), and quartz in the rock c. The specific gravity of the 

 fine-grained rock is 3*01 . 



Porphyry in the New Quarry behind the North Quarry. 



A new quarry has been opened on the reverse slope of the hill in 

 which the North Quarry is located. The rock exposed is fresh 

 and dark, of fine grain, and showing phenocrysts. The microscope 

 shows that orthoclase and quartz form the ground-mass, in which 

 are set numerous badly-formed prisms of orthoclase and some 

 plagioclase with secondary calcite. Ragged flakes of biotite occur, 

 but more common are peculiar spongy masses of green hornblende, 

 this structure being probably due to partial resorption of hornblende- 

 crystals. 



Here also must be noted a fine-grained rock (d in the previous 

 paper, p. 21) found as large reddish-brown masses in the granite at 

 Changi, on Singapore Island (see fig. 1, p. 421). This consists of 

 orthoclase in short, well-formed prisms, a little plagioclase, abundant 

 interstitial quartz in optical continuity over large areas of the field, 

 biotite in small ragged flakes, green hornblende, and abundant 

 apatite. No veins of this rock have been observed. 



1 Basic Masses ' in Quarry No. 1. 



I have already mentioned the occurrence of large, angular ' basic 

 patches ', which are better described as ' basic masses ', in Quarry 

 No. I. 1 The number of those exposed now is very large, and 

 all, with one exception, were at the time of my last visit of the 

 same nature. This exception was a roughly spherical mass about 

 4 feet in diameter, of a dark reddish-brown colour aud fine grain, 

 resembling the fine-grained rock c in the North Quarry. Sections, 

 however, showed a fine mosaic of quartz, orthoclase, and plagio- 

 clase, masses of large quartz-grains, biotite in minute flakes, a little 

 ragged hornblende, and pale-green granules which show some of the 

 properties of monoclinic pyroxene. A black dust is present also. 

 This rock, which cannot strictly be called basic, strongly suggests 

 an included mass of highly altered sediment or fine-grained ash. 

 At one or two points in it granite was visible, probably forming 

 small veins. 



Fig. 3 (p. 426) shows some of the angular masses in the granite. 

 The largest is remarkably like a portion of a dyke, but a close 

 study of the quarry satisfied me that all these dark masses were 



1 Geol. Mag. dec. v, vol. vi (1909) p. 21. 

 Q. J. G. S. No. 263. 2 a 



