a. [f. TUFF sb. + -ACEOUS.] ‘Having the properties of or composed of volcanic tuff’ (Cent. Dict. Suppl., 1909); distinguished from tufaceous in the specific sense.
1882. Geikie, Textbk. Geol., II. II. vi. 164. Tuffs passing gradually into shale, limestone, sandstone, &c. The intermediate varieties have been called ashy shale, tuffaceous shale, or shaley tuff, &c.
