﻿1851.] 



LOGAN — GEOLOGY OF SINGAPORE. 



319 



nic portions of the district, the most general character that we observe 

 is the predominance of felspar and the prevalence of hornblende, — 

 quartz and mica being generally in small proportions, and the latter 

 rare. Well-developed granite of the common type is found in very 

 few localities on the northern side of the Straits, the plutonic tract 

 of Singapore being very deficient in quartz and mica, most of the red 

 clay hills which occur in it being probably decomposed greenstones 

 and highly hornblendic syenites. Even Pulo Ubin, although it pre- 

 sents several decidedly granitic bosses, tends, on the whole, more to 

 the felspatho-hornblendic character, which exclusively prevails to the 

 eastward of it, in Pulo Kirimkin (Nanas), the mainland opposite, 

 Pulo Sijahat, Gunong Bau, and the adjacent hills. The only con- 

 siderable display of proper granite is that on the southern side of the 

 Strait, in the north-east section of Batam and the north of Bintang*. 



With respect to the granulation and composition of the plutonic 

 rocks, every variety may be found, from the most compact hornblende 

 and felspar, through granular greenstones, minutely grained grey- 

 stone, syenite, and eurite, to large-grained granite. In Pulo Ubin we 

 find the following gradations (the hornblende being in general either 

 in nests of small granules mixed with felspar, disseminated in minute 

 particles, or in long thin streaks) : light reddish granite, with quartz, 

 predominating \ granite of a bluish grey tinge ; syenite with felspar 

 in excess ; syenitic greenstone ; greystone ; grey felspar, transparent 

 quartz with some black mica interspersed, and nuclei with the mica 

 in excess ; a quartzo-felspathic basis (pegmatite) with minute par- 

 ticles of mica and hornblende disseminated, in some places sparingly, 

 in others abundantly, so as, on partial decomposition, to give the rock 

 the appearance of finely-ground pepper ; spherical nuclei of mica with 

 a little felspar, surrounded by concentric laminse ; greenish grey sac- 

 charoid felspar, with crystals of quartz and nests of mica sparingly 

 disseminated ; whitish felspar, black mica, and hornblende ; well- 

 crystallized felspar, with dark green hornblende disseminated in gra- 

 nules, cloudy spots, and fibres ; blackish greenstone or hornblende 

 rock ; felspar and hornblende confusedly aggregated ; opake white 

 felspar, tinged green, and blackish green hornblende in very large and 

 distinct granules ; very finely grained blackish greenstone approaching 

 to basalt ; basalt ; opake bluish grey and white saccharoid felspathic 

 and quartzo-felspathic bases, inclosing crystals and grains of horn- 

 blende and translucent crystals of felspar (closely resembling one 

 variety of Vesuvian lava), in some places becoming compact, the horn- 

 blende granules sometimes so minute as to appear like fine black dust 

 sprinkled on snow ; in the group of rocks close to Ubin called S'kodo 

 (from the supposed resemblance of one of the most conspicuous to 

 a frog), there is found a regular large granitic crystallization, the 

 hornblende being in well-defined crystals of various sizes and mostly 

 fibrous. 



3. The Ferruginous Rocks. — The iron-rock and quartz which are 

 found so generally, and in particular localities so strongly developed, 

 occur occasionally in broad irregular patches and bands, but usually 

 * I have not personally examined Bintang. 



