The Nod Glas sediments of Caradoc age in north Wales

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Abstract
Twenty feet to thirty feet of black shale, phosphorite and limestone exposed near Welshpool, Montgomeryshire, exhibit a facies which enables a correlation to be made between the Welsh graptolitic Nod Glas shales of Caradoc age and the shelly Onnia Beds of south Shropshire.Graptolitic evidence suggests that the visible thickness of the Nod Glas near Welshpool belongs to the top of the Dicranograptus clingani zone, and the shelly fauna indicates the zone of Onnia gracilis.At the base of the Nod Glas throughout Montgomeryshire is a phosphatic horizon of variable development.

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