The outcrops are largely hidden under laterite.
Being composed largely of red clays and laterite, the soil is not generally rich, and calls for the patient cultivation of the Chinese gardener to make it really productive.
Laterite is a ferruginous and argillaceous rock, varying from 30 to 200 ft.
Laterite may be roughly divided into two kinds, high-level and low-level laterites.
Geologically, Banka resembles the Malay Peninsula, its formations being mainly granite, Silurian and Devonian slate, frequently covered with sandstone, laterite (red ironstone clay) of small fertility, and alluvium.