Webster's Revised Unabridged Dictionary · 1913

Underclay

Underclay , noun

(Geology) A stratum of clay lying beneath a coal bed, often containing the roots of coal plants, especially the Stigmaria.

Text from the public-domain GNU Collaborative International Dictionary of English, derived from Webster's Revised Unabridged Dictionary (1913). Definitions marked with were added by later GCIDE contributors and are not in the original 1913 edition.

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