- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
Rather than Silurian-Devonian, as proposed by B. N. Koopmans (for reference, see this Bibliography Vol. 31, No. 9, 19 E67-08168), regional geologic relationships support a middle to upper Carboniferous age for the Paleozoic 'Langkawi folding phase.'