The Devonian rocks of North Devon are cut by a system of NW.-SE. oblique-slip faults many of which can be shown to have a dextral transcurrent component. Faults of the system displace members of the early Tertiary dyke-swarm of Lundy. The important Combe Martin Valley fault shifts geomorphological features by one and a half miles laterally and 500 ft. vertically. The age and significance of the fault-system are discussed in the paper.