underclay的翻译，读音
英/'ʌndә,klei/
释义：
n. (煤层下的)底黏土层
n. A stratum of clay lying beneath a coal bed, often
containing the roots of coal plants, especially the Stigmaria.
n. A stratum of clay lying beneath a coal bed, often
containing the roots of coal plants, especially the Stigmaria.