North of the fault, Devonian lava flows and pyroclastic deposits slope gently down, thinning towards the north. These are in part overlain by Old Red Sandstone rocks formed later in the Devonian period. Because the deposits thin towards the north, and there are few signs of volcanic necks within the Ochil Hills themselves, it is thought that the eruptive centres were south of the fault, however these are buried deep beneath the Carboniferous rocks including coal measures which are found beneath the low-lying carse lands to the south.