The main rock that was quarried is dolerite, a medium grained basaltic igneous rock intruded as a sill complex some 30 million years after the sedimentary rocks where the fossils occur.
The base of the main sill is well exposed in the quarry area around the pond and there are a number of interesting geological features that can be examined (see photos below). These are explained in more detail in the excursion guide (see Publications)
