152 ME. J. B. scEivENOR oi^- [June 1912^ 



theMesozoic granite. But a glance at the map, and the recollection 

 that the ore is present everywhere in these beds and that the 

 highest yalues of the beds as a whole are not confined to a zone 

 bounding the granite, will show that this view is untenable. 

 Moreover, could we expect impregnation to form cassiterite as- 

 grains of sand ? 



Again, if it is a case of inipregnation on a great scale, what is the 

 significance of the boulders of tourmaline-rock, tourmaline-schists,, 

 and tourmaline-granite ? It is impossible to assume that these 

 were brought into being by the Mesozoic granite; while, on the other 

 hand, such an assemblage of rocks in a detrital deposit would 

 justify a search for tin-ore. 



In 1910, on the Xinta Tin-Mines land, a very rich patch of 

 ore was found close to the big kaoJin vein mentioned above. A 

 quantity of the ore occurred as masses of sharpJy defined crystals. 

 This was clearly a case of impregnation from the Mesozoic granite, 

 the medium that bore the tin having risen through the limestone. 

 If the balk of the tin-ore in the Gopeng Beds is of similar origin, 

 why does it not generally exhibit the same habit ? 



On the Ulu Gopeng Mine all the tin-ore, so far as is known, 

 comes from veins and stringers in the phyllites and quartzites, and 

 it is all sharply angular, often showing good crystal faces. This- 

 ore was derived from the younger Mesozoic granite, but is quite 

 unlike the bulk of the ore in the Gopeng Beds. 



Finally, if the cassiterite boulders are accepted as an original 

 constituent of the boulder-beds, what difficulty is there in regarding 

 the bulk of the tin-ore in the beds as an original constituent also? 



The mineral constitution of the Gopeng clays and boulder-clays 

 clearly points to the material having been derived from some mass- 

 of tin-bearing granite and rocks altered by it, distinct from, and 

 older than, the Mesozoic granite ; but the Mesozoic granite has. 

 certainly further enriched the beds by impregnating them locally 

 wiyth a second supply of tin-ore. 



(8) The Faulting of the Rocks in the Neighbourhood 

 of Gopeng, and its Connexion with the present Physical 

 Features 



One of the problems that has often presented itself to those who 

 live in Perak, and has called forth some opinions of a rather original 

 nature, is the origin of the limestone hills. It is unnecessary to 

 notice the views that have been put forward in detail, and it will 

 suffice to say that denudation, coupled with the solubility of the 

 rock, has been overlooked. 



In the case of Pahang, where limestone hills also occur, I have 

 failed to find an}- direct evidence that they are due to anything 

 but denudation modified by the solubility of the limestone ; but in 

 1904, during a visit to Sarawak, I found conclusive evidence that 

 there inland cliff's of limestone were fault-faces, the shales that had 

 been faulted down against them having been removed by denudation.. 



