During the final wasting of the ice sheets at the close of the Midlandian, Ireland's final glaciation, a glacier occupying the Moygannon Valley retreated northwards into the upper valley leaving 9 terminal moraines in its wake. These ridges mark periods when the general climatic warming was arrested for a time and the snout of the glacier appeared stationary, the rate of flow neutralised by the speed of melting. In these circumstances, debris released by melting accumulates along the glacier front to form linear ridges, usually of irregular height. At Ballymaconaghy a ridge around a km long, 300 m wide and 15 m high between the river and the minor stream valley to the west contains remnants of 4 such frontal moraines which extend onto the valley sides in the form of round crested ridges and benches. Small exposures show them to consist of diamict, a mixture of gravely fragment sizes. Remnant arcs of two further moraines can be clearly identified perched high on the western side of the valley at Aghavilly, 2 km north of the ridge.
