﻿Vol. 66.] PFLATr TJBIN AND PULA.T7 NANA8. 431 



V. The Relations of the Pulau Ubin Rocks. 



We have now to consider the relations of the various rocks on 

 Pulau Ubin. These (including the Changi rock on the Island of 

 Singapore) may be divided as follows : — 



I. II. 



The normal hornblende-granite with The pyroxene -microgranite in the 

 a little monoclinic pyroxene. South Quarry with dark masses that 



resemble III (1). 



III. IV. 



(1) The porphyry behind tbe North (1) The quartz-norite veins in the 

 Quarry. North Quarry. 



(2) The Changi rock, which has the (2) The fine-grained veins and masses 

 mineral constitution of an amphi- in the North Quarry which have the 

 bole-vogesite. mineral composition of an enstatite- 



spessartite, 1 but not the structure 

 of a typical lampropbyre. 2 

 (3) The masses of quartz-biotite-gab- 

 bro in Quarry No. 1. 



I have already said that Pulau Ubin is a jungle-clad island. It 

 is impossible, except at enormous expense, to hope to run traverses 

 from one quarry to another in such a way that the relations of the 

 different rocks may be made clear ; and it is useless to wait for 

 further information consequent on the growth of existing quarries 

 or the opening-up of new faces, which might involve waiting 

 indefinitely. It is to be regretted, but unavoidable, that the 

 relations of Divisions II & III to the other rocks must for the 

 present remain a closed book, the data available being insufficient 

 for profitable discussion. 



The most important is Division IV, not only on account of the 

 mutual relations of the rocks on Pulau Ubin, but also because a 

 comparison is possible with rocks in the Archipelago. 



The first point that strikes one is that in the North Quarry we 

 have two distinct types of veinstones, one type also occurring as 

 musses included in the granite. The rock of coarser grain forms the 

 thinnest veins in the quarry. It might be argued that this is due 

 to these being formed by segregation of certain constituents of the 

 granite along planes in the molten magma. Did the granite show 

 any sign of foliation, or had it been proved to contain enstatite, 

 this argument might hold good ; but, in the absence of any such 

 support, the veius can only be regarded as intrusive, and we must 

 turn to some other explanation for the variation in grain. This 



1 In Geol. Mag. dec. v, vol. vi (1909) p. 22, I said that this rock might 

 be described as enstatite-vogesite : enstatite - spessartite is a more correct 

 definition. 



2 I refer to the ' panidiomorphic ' structure. 



