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Published online by Cambridge University Press: 01 May 2009
The history of investigation of the rocks at present classed as Precambrian in the type region of the Cambrian system in the north-west corner of wales (Cambria), where that system was first named and its lower limit locally defined, is reviewed. The Arvonian volcanic series was originally included in the Cambrian System, the Monian metamorphic group remaining as Precambrian.