A large, bowl-shaped chert nodule has been found in the lower Carboniferous Hawes limestone at the base of the Yoredale series near Marsett. The nodule, the only one ever found in the Hawes limestone, is described, and it is concluded that its formation was due to deposition of silica in a cavity developed in a solution plane in the limestone subsequent to consolidation. The source of the silica was probably disseminated silica within the limestone, both organic and mineral.

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