A volcanogenic clay bed (tonstein) has been identified in the Balcomie Beds of the Inverclyde Group near Crail, East Fife. Its chemical composition suggests an undersaturated alkaline magma source. This horizon may be contemporaneous with the early Carboniferous Garleton Hills trachytic lavas of East Lothian (346 Ma). This would make it the earliest expression of Carboniferous volcanism preserved in Fife, and also the earliest occurrence of a tonstein in Fife.

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