consisting of the Philippines provinces of Basilan, Sulu, and Tawi-Tawi; hence, the archipelago is sometimes referred to as Basulta, derived from the first syllables of the three provinces.

The archipelago is not, as is often supposed, the remains of a land bridge between Borneo and the Philippines. Rather, it is the exposed edge of small submarine ridges produced by tectonic tilting of the sea bottom. Basilan,