WESTLINE is a 450 km long near-normal-incidence seismic reflection profile crossing the Rockall Trough from the Rockall Bank to the Irish coast. Beneath Rockall Bank and the Irish shelf unreflective upper crust overlies reflective lower crust and upper mantle. Crustal reflectors beneath the Irish shelf are interpreted as Caledonian. The NW slope of the trough is dissected by a series of east dipping faults forming small sediment filled half grabens. The steep SE slope is formed by the Erris Ridge. The floor of the trough is formed from rotated blocks separated by mainly east-dipping faults. Wedges of sediment fill half grabens formed by this faulting. There is no evidence for oceanic crust or a 'reflection Moho' within the trough. The floor and slopes of the trough are blanketed by c. 4 km of parallel-bedded sediments. The lower part of the parallel-bedded sequence is intruded by sills and dykes that do not extend above a minor unconformity. It is suggested that the bulk of the sediment preserved in the Rockall Trough accumulated during and following a major rifting event in the early or mid-Cretaceous.