The upper Llandovery rocks of North Connemara record a gradual marine transgression at the northern margin of the Lower Palaeozoic geosyncline. The lowest rocks are red sandstones deposited from mainly southward flowing rivers• These are overlain by lagoon and coastal barrier sandstones and siltstones, and deeper water shelf siltstones. Red marine siltstones and mudstones, deposited in 100 to 200 m depth of water, are found near the top of the Llandovery sequence. Deeper water turbidite conglomerates and sandstones, with some thick mudstones, both overlie and laterally interfinger with the sequence of non-marine and shelf sediments. Basement faults controlled rates of subsidence during shelf sedimentation, and topographically defined the margins of turbidite accumulating basins. A palaeogeographic synthesis of the area is presented.