(UNDER-1 5 b.)
1840. W. Logan, in Trans. Geol. Soc., Ser. II. VI. 491. In South Wales, immediately below every regular seam of coal,… lies a bed of clay, which is commonly called underclay, underclift, understone.
(UNDER-1 5 b.)
1840. W. Logan, in Trans. Geol. Soc., Ser. II. VI. 491. In South Wales, immediately below every regular seam of coal,… lies a bed of clay, which is commonly called underclay, underclift, understone.
