The geology of Singapore Island; with a geological sketch map
J.B. Scrivenor, a geologist with the Straits Settlements Geological Department, published this general geological account of Singapore Island in 1924, synthesizing fieldwork conducted over several visits with the bulk of observations made in 1922. The paper establishes the stratigraphic framework of the island—placing its sedimentary rocks in the Upper Triassic (Rhaetic) and its granite as a younger intrusive body—and situates Singapore within the broader tectonic and lithological patterns of the Malay Peninsula.
Summary
Scrivenor’s paper provides a systematic, if necessarily approximate, geological map of Singapore Island, acknowledging that heavy weathering and dense vegetation make precise formation boundaries difficult to determine. The island’s geology is dominated by two major units: a southern and western belt of sandstone and shale (weathered quartzite), and a central and eastern expanse of granite. The sedimentary rocks form the Mount Faber Ridge, the hills of Singapore Town (Mount Palmer, Mount Wallich, Fort Canning, Pearl’s Hill, Mount Sophia, Mount Emily), and the islets of Pulau Brani and Blakang Mati. The granite underlies the central and eastern portions of the island, with its most prominent surface expressions being Bukit Timah and Bukit Panjang in the west, and the quarries of Pulau Ubin and Changi in the east.
The structural relationship between these units is a central finding. The sandstone and shale exhibit high dips—reaching 75° at the now-removed Mount Guthrie and approaching vertical at the entrance to Keppel Harbour—indicating significant tectonic disturbance. The granite, by contrast, shows no evidence of comparable deformation in its well-exposed quarry sections. Scrivenor concludes that the granite is younger than the sedimentary strata and was intruded as a consequence of the earth-movements that tilted the latter. No metamorphosed rocks were found at the contact, further supporting this interpretation.
The paper also addresses minor igneous occurrences (quartz-porphyry, dolerite, trachyte, andesite, and volcanic ash) and a distinctive “high-level alluvium” forming low hills of 50–100 feet above sea level along the Changi and Tampines Roads. This alluvium, composed of feldspar-rich sand with shale pebbles and staurolite among the heavy minerals, is interpreted as a former terrace deposit of the Johore River from a period when Singapore was connected to the mainland.
Key Findings
- The sandstone and shale of Singapore are of Upper Triassic (Rhaetic) age, based on a marine molluscan fauna described by R.B. Newton (1923) that shows specific connections with the St. Cassian Beds of the Austrian Tyrol and the Muschelkalk of Germany, and is lithologically continuous with the Myophorian Sandstone of Pahang (pp. 4–5).
- The granite is structurally younger than the sedimentary rocks: the high dips in the sandstone and shale (up to 75°) contrast with the absence of comparable deformation in the granite, indicating the granite was intruded following the tectonic event that tilted the strata (p. 4).
- A compositional gradient exists in the granite from west to east: the western margin (Bukit Timah, Bukit Panjang) is an acid type with high silica, abundant quartz and feldspar, and limited dark mica, while the eastern portion (Seletar, Changi, Pulau Ubin) is a hornblende-granite with abundant dark mica and hornblende (p. 6).
- Tin-ore (cassiterite) was found in a pocket at Bukit Panjang in 1906 and later in quantity at Bukit Mandi; molybdenite was recovered from a Bukit Timah quarry around 1921, confirming the economic potential of the western acid granite (p. 6).
- The high-level alluvium of the eastern island (50–100 ft above sea level), exposed at Tanah Merah Kechil, is interpreted as a Quaternary terrace of the Johore River formed when Singapore was still joined to the mainland, analogous to terraces in Sumatra reaching 140 m above sea level (p. 7).
- The igneous sequence at Pulau Ubin comprises: (1) consolidation of hornblende-granite, (2) intrusion of quartz-norite, quartz-biotite-gabbro, and enstatite-spessartite veins, and (3) later granitic (aplite) intrusions cutting some of the earlier veins (p. 7).
Conclusion
Scrivenor positions Singapore Island as a small but geologically significant fragment of the Malay Peninsula’s structural framework: the granite belongs to the great tin-bearing mass exposed across the Peninsula’s ranges, while the sandstone and shale represent a widespread shallow-water formation deposited on the ancient Gondwanaland coast. He emphasizes that the island’s fossiliferous Triassic rocks and extensive granite quarries make it a valuable natural laboratory, and he calls for further palaeontological work on the islets south of Blakang Mati and systematic search of the high-level alluvium for prehistoric remains.
Context
- The paper was published in the second volume of the Journal of the Malayan Branch of the Royal Asiatic Society, a periodical that served as a primary venue for scientific and historical scholarship on the Straits Settlements and the Malay Peninsula during the colonial era.
- Scrivenor’s earlier publications in the Geological Magazine (1908, 1909) and the Quarterly Journal of the Geological Society (1910) on Singapore’s igneous and sedimentary rocks form the specialist foundation upon which this general account builds.