At The Baths, although volcanism accounts for much of the Virgin Islands, we see granite that eroded into piles of boulders on the beach. Granite forms from the slow cooling of magma at depth nowhere close to surface volcanoes.
The granite only appears at the surface after geologic ages have eroded away all the overburden covering it. Once exposed, erosion continued to isolate the granite into large boulders and round their surfaces. The boulders form natural tidal pools, tunnels, arches, and scenic grottoes that are open to the sea. The largest boulders are about 40 feet (12 m) long.