Tear faults cutting the Barnesmore Granite in County Donegal are described. The Lough Belshade fault trends N.E.–S.W., and there has been a lateral movement along it in a left-handed or sinistral sense of 2·2 miles; it is believed to be of the same age as the Great Glen Fault. The Barnes Lough Fault crosses and displaces the Lough Belshade fracture, and may be, in part at least, Tertiary. Although the movement along it is much smaller, it has taken place in the opposite sense.