Most of Wales is underlain by a thick pile of sedimentary rocks, ranging in age from Cambrian to Devonian, together with volcanic and intrusive rocks which are exposed mainly in the north and south of the country. These rocks collectively constitute the fill of the Welsh Lower Palaeozoic Basin, a major region of prolonged subsidence which developed as a marginal basin on the southern continental flank of the Late Precambrian—Early Palaeozoic Iapetus Ocean. It was deformed and weakly metamorphosed, mainly in Early Devonian times, during the Caledonian Orogeny in response to plate collision processes.
KeywordsHinge Line Fold Hinge Crenulation Cleavage Accretionary Lapillus Caledonian Orogeny
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