[? for bas- or base-coal, as in base coin.] A miners’ term for shale stained dark by vegetable matter. Cf. BAT sb.2 11.
1686. Plot, Staffordsh., 131. Bass or freestone above, and Ironston or earth, below.
1861. E. Hull, Coal-field’s Gt. Brit., 54. Some of the shales are so highly carbonaceous as to be nearly black, and form impure coal called ‘bass.’
