The geology of the Langkawi Islands: with a geological sketch map
Scrivenor and Willbourn, geologists attached to the Federated Malay States survey, published this paper in 1923 in the inaugural volume of the Journal of the Malaysian Branch of the Royal Asiatic Society. Drawing on fieldwork conducted in 1919, 1920, and 1922, it presents the first systematic geological account of the Langkawi archipelago, demonstrating that the islands expose a Carboniferous sedimentary sequence intruded by porphyritic granite and that the group is undergoing recent tectonic elevation relative to sea level.
Summary
The paper addresses the fundamental problem of reconstructing the geological history of an island group where the coastline is so extensive and varied that the broad structural outline can be read from surface exposures alone. Scrivenor identifies three stratigraphic groups—oldest quartzite and shale, a thick limestone with an intercalated deep-water shale and quartzite series, and youngest quartzite and shale—all conformable to one another, forming a sequence that begins and ends in shallow-water conditions with a prolonged deep-water phase in the middle. The granite, intruded into these rocks, is porphyritic and rich in tourmaline, and its contact effects range from saccharoid marble to bands of wollastonite, garnet, and pyroxene. The structural history is read from dips and folds observable on the islets, with two localities flagged as anomalous: one where beds dip toward rather than away from the granite, and another where a mass of crystalline limestone is interpreted as having sunk into still-viscous granite during intrusion (pp. 339–344).
The mineral-economic assessment is cautious. Beach-sand concentrates from multiple localities yield zircon, ilmenite, and tourmaline as dominant heavy minerals, with no cassiterite detected, leading the authors to conclude that tin-ore is absent from the nearby granite. A small quantity of scheelite from a single concentrate on Tubah is noted as the only potentially economic find, though the authors advise against active prospecting unless tungsten prices rise. A bismuth-copper-sphalerite contact-metamorphic deposit, opened in 1922 near Kuah, is described as irregular in form with no clearly defined lode walls, and its full extent remains unproved (pp. 343–345).
The paper closes with two broader arguments of regional significance. First, the Langkawi exposures help resolve a classification problem on the mainland: some shales and quartzites previously mapped, for want of fossil evidence, as younger than the Carboniferous “Raub Series” may in fact belong to that series, because the Langkawi sequence shows no chert or coarse conglomerate that would indicate Triassic or Jurassic age. Second, extensive sea-sand deposits and old beach-lines across the islands provide clear evidence of recent uplift, implying that the Langkawi group will eventually become united with the Perlis mainland as the elevatory movement continues (pp. 345–347).
Key Findings
- The oldest quartzite-and-shale group (C) and the limestone group (B) are each estimated at approximately 5,000 feet in thickness; the intercalated deep-water shale-and-quartzite series within the limestone measures 700 to 1,200 feet (pp. 340–341).
- The limestone is almost certainly Carboniferous in age, based on correlation with the mainland; fossils recovered include bryozoans, crinoid stems, and flattened univalve (gastropod) shells, but no nautili—correcting an earlier report by Dr. Bland in Newbold’s 1839 British Settlements in Malacca (p. 341).
- Black-sand concentrates from five beach localities contain zircon, ilmenite, and tourmaline as the dominant heavy minerals; no cassiterite was found in any sample, and only trace scheelite occurred in a single concentrate from the east coast of Tubah (p. 343).
- A bismuth-copper-sphalerite mine was opened in 1922 at a contact-metamorphic zone approximately 1½ miles from Kuah; the ore body is irregular, hosted in wollastonite-green garnet rock, and shows no strongly marked lode walls, though faulting post-dates mineralisation (pp. 344–345).
- Recent tectonic elevation is evidenced by extensive sea-sand deposits near Padang Mesirat overlying two distinct old beach-lines, and by a long NNE–SSW depression in southern Dayang Bunting that appears to be a former continuation of the strait now separating it from Tubah (pp. 346–347).
- The highest point, Gunong Raya, is a granite peak of 2,880 feet; the quartzite range in the north-west of Pulau Langkawi reaches peaks over 2,000 feet (p. 330).
Conclusion
Scrivenor and Willbourn establish the Langkawi Islands as a critical reference section for the Carboniferous geology of the western Malay margin. Their definitive contribution is twofold: the conformable succession of shallow-water, deep-water, and shallow-water sedimentation within a single Carboniferous cycle, and the demonstration that the islands are being actively raised, a process that will ultimately weld them to the Perlis coast. The paper thus serves both as a foundational local geological survey and as a corrective to the mainland stratigraphic map.
Context
- Both authors held salaried positions within the colonial geological survey of the Federated Malay States (Scrivenor as Geologist, Willbourn as Assistant Geologist), and the paper was produced as part of that administrative programme of territorial mapping and resource assessment.
- The study draws exclusively on the authors’ own field observations, hand-specimen microscopy, and beach-sand concentration work; no prior published geological account of the Langkawi Islands existed, making this the baseline reference for all subsequent work on the group.