﻿428 MR. J. B. SCRIVENOR ON THE ROCKS OF [Aug. I9IO,. 



crystalline grains which are probably secondary hornblende, and a 

 little calcite. 



But the most remarkable feature of these tuffs is the presence of 

 fragments of altered granite, and it is fortunate that, even though 

 the large quarries on this island be abandoned, there will remain 

 on the north side of the island an exposure washed by the water 

 of the Straits, which, therefore, unlike most sections in the 

 tropics, may be expected to endure, showing these granite frag- 

 ments clearly, and showing, moreover, that the pieces of granite 

 seen are not sections of veins. 



Sections from the fragments of granite show that it is a biotite- 

 granite, with orthoclase and small crystals of plagioclase often 

 included in the orthoclase. The biotite is somewhat altered. In 

 the felspar and biotite crystals there is a considerable develop- 

 ment of secondary green hornblende ; secondary brown mica is 

 associated with the original biotite, and often occurs in the felspar, 

 also. 



I have no doubt that the tuffs and lavas of Pulau Nanas form an 

 extension of the Pahang Volcanic Series, and that the granite 

 fragments have been as much affected by the contact-metamorphism 

 of the younger granite as the volcanic rocks. The last must have 

 been erupted on the earth's surface or on the sea-bottom, and it 

 follows, therefore, that the granite mass from which these fragments 

 were derived had consolidated much earlier. We are safe, then, in 

 saying that these fragments are conclusive evidence of a pre-Car- 

 boniferous granite in the Peninsula ; and I may mention here an 

 interesting discovery of two small pebbles of schorl-rock in the 

 Tembeling conglomerate, which is certainly older than the granite 

 that now forms the backbone of the Peninsula. These pebbles may 

 have come from the pre-Carboniferous granite ; but as tourmaline 

 in a granite mass always suggests the possibility of finding tin-ore 

 also, I must add that hitherto I have found no detrital tin- ore in 

 rocks older than the tin-bearing granite. 



IV. The Relations of the Pitlat/ Nanas Granite Fragments and 

 the Ptjlau Ubin Normal Granite to the Granite Masses of 

 the Archipelago. 



The fragments of granite and the pebbles of schorl-rock are the 

 only evidence available so far of pre-Carboniferous rocks in the 

 Peninsula. This is a fitting place to discuss the relationship of 

 the pre-Carboniferous granite and the younger granite l to granite 

 masses described by the 'Dutch geologists in the Archipelago. 



1 I have elsewhere (' Geologist's Keport of Progress : Sept. 1903- Jan. 1907 ' 

 p. 13) discussed the possibility of the tin-bearing granite having been erupted 

 at two distinct periods. The balance of evidence is against this view. 



