From the pitted nature of the rock, Barnacle Bill is an igneous (lava-like) rock that cooled rapidly on the surface.
(Barnacle Bill; is; an igneous (lava-like) rock that cooled rapidly on the surface) (an igneous (lava-like) rock; cooled rapidly; L:on the surface)
Barnacle Bill an igneous (lava-like) rock
is cooled rapidly
an igneous (lava-like) rock that cooled rapidly on the surface
L:on the surface