and important basalt, hyaloclastites and breccias erupted or sedimented during the Caradocian Epoch of the Ordovician Period. The Group includes (in descending order, i.e. oldest last):
*Upper Crafnant Volcanic Formation
*Middle Crafnant Volcanic Formation
*Lower Crafnant Volcanic Formation

The Tal y Fan Volcanic Formation occurs towards the northeast and the Bedded Pyroclastic Formation