This is a working quarry in the Lower Basalt Formation. The rocks were originally lava flows pouring from an unidentified volcano or fissure somewhere in the immediate area around 60 million years ago. The hot gases escaping from the molten rock formed streams of bubbles which became trapped as vesicles as the rock cooled. Hot groundwater circulating through the newly formed basalts deposited zeolite minerals in these small cavities which were thus converted to amygdales (mineral-filled vesicles). The Antrim basalts are world famous for the variety and form of the zeolites they contain.
Due to continuous working, it is at present impossible to say which zeolites may be left in the quarry when activity ceases.