22 J. B. Scrivenor — Igneous Bocks of Singapore. 



Borneo,' says that pyroxene seldom occurs, and is restricted to the 

 varieties rich in hornblende. It occurs as mouoclinic augite or 

 rhombic hypersthene. The specific gravity of the Pulau TJbin rocks 

 makes it hard to regard them as pyroxene-bearing granites ; still, it 

 may be noted here that in his Beschrijving van ecn (icdeclte van 

 SumatnCs Westkusf^ I)r. R. D. M. Verbeek describes " augite- 

 bearing granite or quartz-augite-diorite ", ^ and " augite -bearing 

 syenite-granite "* whose chemical composition probably approximates 

 that of the Pulau TJbin rocks. On the other hand, Charnockite * 

 (sp.g. 2"67), the hypersthene-bearing granite of the Indian Peninsula, 

 is distinctly separated from these rocks, not only in point of age but 

 in mineral composition; while the references made by Rosenbusch,® 

 Zirkel,' and Dr. TealP to granite containing rhombic pyroxene do 

 not favour their being regarded as phases of the normal granite. 



The rocks a and b are not unlike some hypersthene-bearing rocks 

 found by the writer in Sarawak. These are quartz-hornblende- 

 norites, and the Pulau Ubin rocks a and b might be described as 

 quartz-biotite-norite, but the amount of quartz present is considerable, 

 and the extinction angles of the plagioclase are not high. The 

 quartz-hornblende-norites of Sarawak are connected genetically with 

 hypersthene andesites, lavas that are wide sjiread in the Malay 

 Archipelago, and regarded as dating from the close of the Eocene. 

 The granite of the Archipelago being earlier, it is possible that the 

 Pulau Ubin rocks were derived from the same magma as the Sarawak 

 norites, and should be regarded as belonging to a later j^eriod of 

 eruption. 



Considered apart, the fine-grained rock e^ on Pulau Ubin, and the 

 fine-grained rock d at Changi, are interesting on account of their 

 resemblance to lamprophyres. The former might be described as 

 enstatite-vogesite,'" while the latter is an amphibole vogesite. 



' N. Wing Easton, " Geologis eines teiles von West Borneo'': Jaaib. v. li. 

 Mijnwezen in Ned- 0.- Indie, Wetenschap. Gedeelte, Batavia, 1904. 



2 Batavia, 1883. ^ Qp. cit., pp. 205-6. * Op. cit., p. 210. 



* T. H. Holland, Mem. Geol. Suiv. India, vol. xxviii, pt. ii, "The 

 Chamockite Series, a group of Arclitran hypersthenic rocks in Peninsular India." 



* Eosenbusch, 3Iassige Gesteine, p. 60. 

 ' Zirkel, Petrographic, vol. ii, p. 13. 



* J. J. H. Teall, "On some Quartz -Felsites and Augite Granites from the 

 Cheviot Disti-ict" : Geol. Mag., 1885, p. 115. 



* In " The Rocks of Pulo ( = Pulau) Ubin" (Verhandel. Bataviaaseh. Geuootsch. 

 Kunst. Wetenschap., vol. xxii, also published in Essays relating to Indo-Clnna, 

 ser. II, vol. i, pp. 21-71) Logan notes a iine-grained rock, " blackish-green 

 hornblende, or a very iine-grained black greenstone approaching basalt." This may 

 be the writer's (; weathered. Logan also mentions, however, a remnant of a basalt 

 dyke between Pulo ( = Pulau) Tarn (Kitani ?) and the west point of Pulo ( = Pulau) 

 Ubin, and he noted a bit of basalt adhering to a large syenitic block. This very 

 likely refers to basic dykes cutting the granite such as are known elsewhere. Logan's 

 observations were made prior to 1847, and those acquainted with the tropics will 

 realize that all trace of the exposures mentioned may have disappeared. 



'o Eosenbusch (op. cit., p. 511) mentions hypersthene in a minette from near 

 Freiburg and bronzite in Hartz Kersantites. The subordination of the biotite to the 

 other feiromaguesian minerals in the Singapore rocks makes it necessarv to reo'ard 

 them as vogesites. 



