Due to the volcanic nature of the island, most of the rocks have a volcanic origin and are of basic nature, thus constituting, in surface and in volume, almost the entire immersed part of the island.

The sedimentary formations do not present much representation, however, they are important simply because in some cases they contain fossils. The terrestrial sediments are merely dunes, landslides, scree and torrent slopes. As for the marine sedimentary formations, they are composed of conglomerates, fossiliferous limestones and calcarenites, gravel beds and beach sand.

Nowadays, limestones have formed an outcrop of small size, located in the right margin of the São Vicente riverside, at an altitude of 380 m. This outcrop is essentially composed of conglomerates, which are thought to be in the base of that marine sedimentary deposit, leaving some evidences of fossiliferous limestones at the top.

There are also some conglomeratic breccia deposits which are the result of a sedimentary formation composed of thick deposits of torrents, extremely compact and cemented, formated by the very intense and constant rain of an extremely different climate from the one we know today.

As to the nature of this deposit's sediments, it doesn't seem to be very varied, among which are basalts with pyroxene phenocrystals, olivine basalts and vacuolar basalts. Many of these sediments are remains of separation prisms and others present a ball-shaped separation. These sediments have a greyish black and vary from coarse to thin.