The first three listed above form a part of the Old Red Sandstone sequence and occur only in the easternmost part of the area. The summit which is towards the southwestern end of Long Mountain is formed by rocks of the Knucklas Castle Formation. Numerous faults cut the succession. There are a number of glaciofluvial deposits around the margins of Long Mountain, dating from the last ice age. Pockets of glacial till of similar age occur in some of the valleys.