The high, open uplands of the Slieve Beagh area are extensively capped with sandstones and mudstones of the Meenymore Formation but in several small areas faulting has revealed the Dartry Limestone beneath. The combination of an upland with relatively high rainfall consisting of thick, pure limestones under an impermeable surface cover should be an ideal setting for karst development, particularly extensive cave systems but nothing of significance has so far been found in the area. The only indication of karst processes is a depression about 100 m in diameter, called Sumera Hole, about 1.5 km west south west of Glenoo Bridge, where a few local streams sink into the ground. It is thought that the many small Tertiary dykes in the area, cutting across the tilt of the limestones, slow local underground drainage and consequently inhibit cave formation.
