Tufa

(tu'fah,) or TUFF. (Geol.) A rock composed of small particles of stone, which i ued in the shape of dust from a volcano; or as mud, that is, dust mingled with steam. In volcanic countries there are strata of T., some of which had been originally thrown into the sea, and contain marine organic remains; others have been penetrated by water, holding calcareous matter in solution, by which the tufaceous particles have been bound together into a hard ma susceptible of a good polish. T. frequently alternate with beds of basalt and trachyte. [s. 910]