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to be intruded was one in which quartz and topaz are constant con- 

 stituents, and it is called in this paper the quartz - to pa z r c k. It 

 occurs in veins, the biggest of which are about 15 feet thick. Some 

 of these veins appear, at their outcrops on the side of the mountain, 

 to be regular in form and lying almost flat, thus resembling sills. 

 Others, however, are very irregular both in their course and in 



their form. Some are 

 only an inch or so thick. 

 The second rock to be 

 intruded was topaz- 

 aplite. This cuts both 

 the porphyritic granite 

 and the quartz-topaz 

 veins. On the north 

 side of the mountain it 

 forms large masses. On 

 the south it is not so 

 abundant, and one clear 

 section shows distinct 

 veins of it. I have 

 called this rock an 

 aplite, but it is rather 

 coarse-grained for an 

 aplite, and nowhere 

 coarse-grained enough 

 to be called a pegma- 

 tite, except as will be 

 described later, at the 

 border of certain parts 

 of it. 



Fig. 2 (p. 365) shows 

 dia gramma t i ca 11 v the re - 

 lations of the porphyritic 

 granite, the quartz- 

 topaz rock, and the 

 topaz-aplite. The cen- 

 tral vein of quartz- 

 topaz rock has not yet 

 been proved to exist, but 

 the fact that Gunong 

 Bakau stands out as a 

 peak on the granite 

 mass of the Main Range 

 leads one to suspect 

 some such hard core. 

 Fig. 3 is a sketch of 

 an actual section, showing the quartz-topaz veins cutting the por- 

 phyritic granite, and the topaz-aplite cutting both these rocks. 



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