In "S.O.S.", Bernard starts building an SOS sign from black rocks he found in a lava field 1/2 mile inland from the beach. The Island has igneous (volcanic) origins, like almost all islands in the Pacific, so it is composed in great part of a black volcanic rock called basalt. Igneous rocks contain large proportions of metal elements such as iron and manganese. This gives the rocks magnetic properties which form anomalies in the earth's natural magnetic and gravitational field. Lava-formed coastlines are also apparent in the rocky vistas seen in the following episodes: