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Published online by Cambridge University Press: 01 May 2009
In Green's “Geology of the Yorkshire Coalfield” (Mem. Geol Surv., 1878, p. 471) reference was made to the occurrence below the Ackworth rock of a band of black shale, which it was said “contains Aviculopecten in plenty, and shows that incursions of the sea continued to occur even up to these comparatively late portions of the Coal Measure period.”