Geology of Lancashire

The geology of Lancashire in northwest England consists in the main of Carboniferous age rocks but with Triassic sandstones and mudstones at or near the surface of the lowlands bordering the Irish Sea though these are largely obscured by Quaternary deposits.

A small fault-bounded area of rocks of Wenlock age lies to the north of Ireby in the extreme north of the county.

Rocks originating in the Carboniferous Period underlie the uplands of eastern and north Lancashire. Listed in order of succession ie lowermost/oldest first, they comprise the various limestones, mudstones, siltstones and sandstones of the Bowland High Group and Trawden Limestone Group, Craven Group, Millstone Grit Group, Pennine Coal Measures Group and Warwickshire Group.

The Bowland High Group is bundled together with the Trawden Limestone Group in the Carboniferous Limestone Supergroup. Together they include sedimentary sequences developed during the Tournaisian on isolated structural highs or horsts, namely the Bowland High and the Central Lancashire High. The Bowland High Group comprises the older Chatburn Limestone Formation and the younger Clitheroe Limestone Formation. These are largely limestone sequences but with subordinate mudstones and siltstones. The Trawden Limestone Group is not known at the surface but is proved in numerous boreholes. It is not divided into formations.

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