underclayn.
/ˈʌndəkleɪ/, U.S. /ˈəndərˌkleɪ/ A bed of clay beneath a stratum, now spec. under a seam of coal.
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the world > the earth > minerals > mineral deposits > features of stratum or vein > [noun] > material below > below coal
thill1329
underclay1660
sloom1803
underclift1840
warrant1847
swad1860
spavin1870
undercliff1883
under-earth1883
1660 J. Childrey Britannia Baconica 58 The rains that fall, wash by degrees the uppermost mould down into the Valleys,..but leaves the underclay behind.
1840 W. Logan in Trans. Geol. Soc. 2nd Ser. VI. 491 In South Wales, immediately below every regular seam of coal,..lies a bed of clay, which is commonly called underclay, underclift, understone.
1845 C. Lyell Trav. N. Amer. I. 84 I was curious to know whether the Stigmariæ would be found here in the under~clays.
1867 W. W. Smyth Treat. Coal & Coal-mining 25 The floor, thill, or seat..of the coal is an underclay, generally good for fire-brick.
This entry has not yet been fully updated (first published 1921; most recently modified version published online March 2022).
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