378 ME. J. E. SCEIYEXOE OX THE [Dec. 1914? 



formation may have been due. In the first place, there is a minor 

 point that should be made clear. Grunong Bakau is a peak situated 

 almost in the centre of the granitic Main Eange of the Peninsula. 

 There are other instances of tin-deposits not very far away simi- 

 larly situated, and at first sight they all seem to contradict ex- 

 perience elsewhere, namely, that tin-deposits are generally found 

 on the periphery of a granite mass. This, however, is not the case. 

 In three localities on the Main Range sedimentary rocks are known 

 to cap the granite near the centre of the range. In one of these, 

 quartzite and phyllites cap the highest peak in the whole chain, 

 Grunong Riam, or Kerbau, in the Kinta District (altitude, 7160 

 feet). There is, then, good reason to suppose that the present ridge 

 of the range coincides approximately with the top of the original 

 granite intrusion, and we can therefore regard Grunong Bakau as 

 being near the vertical limit of the granite-mass. This preservation 

 of the limits of the granite-mass is one of the factors that has 

 endowed the Malay Peninsula with such enormous mineral wealth 

 as compared with Cornwall, where the granite -masses have been 

 planed down by denudation. 



The current theories postulating the intrusion of pegmatite and 

 the formation of tin-deposits in a granite-mass by pneumatolytic 

 action during the last stages of the consolidation of a granitic 

 magma, are now so familiar as to need no exposition here. It is 

 clear, however, that in the case of the rocks of Grunong Bakau 

 there were magmatic processes in operation that differed from these 

 which are believed to have generally taken place. 



The sequence of events in the mass now forming the peak of 

 Grunong Bakau is clear. First, the porphyrinic granite consoli- 

 dated ; then the quartz-topaz veins were intruded ; and then the 

 topaz-aplite arrived. 



First, granite rich in felspar consolidated ; then, a rock without 

 any felspar was intruded into it ; and then, another rock rich in 

 felspar invaded the mass of granite. 



Therefore, before the last part of the magma capable of afford- 

 ing felspar had consolidated, veins of a rock without any felspar 

 at all were intruded. This is not what would be expected in the 

 differentiation of a magma, and it is interesting to consider how it 

 can have come about. 



It cannot be proved that the topaz and tourmaline found in the 

 granite are, even in part, original rock-constituents, but they may 

 be so. This, and the proved trace of lithia in the biotite make one 

 suspect that, before the granite consolidated, fluorine, boron, and 

 lithium were present throughout the mass in small quantities. As 

 the last products of an acid magma are generally richer in these 

 elements than the granite itself, we may suppose that a concen- 

 tration of them takes place as solidification progresses. How this 

 takes place and how the elements move in the magma we cannot 

 tell, but they are probably combined with other elements and 

 in the state of gas, and I think it is possible to account for the 

 quartz-topaz veins by some such hypothesis as the following. 



