Chai Peng, L., and M. Hakif Hassan. “Contributions from the Geology of Northeast Langkawi to Refining the Mid-Palaeozoic Stratigraphy and Palaeogeography of Peninsular Malaysia”. Malaysian Journal of Science, vol. 24, Apr. 2005, pp. 15-23, https://samudera.um.edu.my/index.php/MJS/article/view/8814.