The supposed Laurentian margin in western Ireland is separated from an Ordovician arc-related basin by the Clew Bay Complex and two Silurian successions, informally termed the Croagh Patrick Silurian and the Louisburgh Silurian, whose relationships are enigmatic. Palynomorphs, tubular structures and sheets of cuticle from turbidites within the Clew Bay Complex indicate a Silurian (Wenlock) age. In the light of these new data and reappraisal of contacts, the Croagh Patrick Silurian is now considered to be in tectonic contact with the Clew Bay Complex. The Louisburgh Silurian may also be in tectonic contact with parts of the Clew Bay Complex and unconformable on other parts, but is probably younger than previously thought. The Silurian age of elements of the Clew Bay Complex, and the relationship of the complex with other Silurian successions in western Ireland, indicate that significant deformation occurred in this part of the Caledonides during mid to end Silurian times, and imply that significant Silurian-Devonian terrane movement took place.