The Drumarg Conglomerate Formation is thought to have formed during the Permian, 250 million years ago. It consists of angular fragments or clasts (therefore is technically a breccia) of Carboniferous limestone around 20mm in diameter, suspended within a red-brown medium grained sandstone matrix. Many of the grey-coloured limestone clasts have been stained pink around the edges through contact with the sandstone.
Drumarg Conglomerate was quarried in Red Barn Quarry, Armagh (now built over) and outcrops in the inactive quarry at Rock Road, Armagh. It was used extensively in Armagh city and weathers well over time.