The Caledonides of west Mayo and northwest Galway in Ireland can be subdivided into three structural units. First, within a narrow E-W-trending belt of amphibolite-facies schist in the Clew Bay area, there is evidence of pre-Caledonian structural and metamorphic events. This basement schist of uncertain age is overlain tectonically by the Erris schists, which extend 40 mi northward and which, with the Connemara schists of northwest Galway, represent the Early Caledonides. The succession of these schist groups is comparable with that of the Moine and Dalradian of Scotland. Large F₁-F₄ folds are associated with M_1...