Abstract In eastern and central Ireland, most of the Silurian is eugeosynclinal and lies with little or no break on upper Ordovician beds. However, in the west there is more variation in facies, and Silurian deposits older than C₄-C₅ age (high upper Llandoverian) are not known. In Galway and Mayo, Silurian rocks lie unconformably on older beds. The Dingle peninsula in southwest Ireland has a shelf facies containing Wenlockian acidic volcanic rocks, but the relations with pre-Silurian beds are obscure.

The ages and geographic distribution of sedimentary facies and volcanic rocks in western Ireland do not correspond in detail to those of northeast Newfoundland, and the absence of a marked early Silurian marine transgression in Newfoundland also might suggest some degree of separation. The fact that marine species were common to both sides of the Atlantic during the Silurian does not prove close proximity.