FLAG-Stone, a genus of argillaceous earths, of a grey, yellowish, or reddish-white colour; not giving fire with steel, nor effervescing with acids. Its specific gravity is from 2600 to 2780. Sometimes it is found compact, and sometimes like the argillaceous grit; in which case its gravity is less. Its general use is for flooring houses, though sometimes it is made use of for covering them. There is also a calcareous flag-stone found near Woodstock in England. It is of a yellowish-white colour, and moderately hard, containing a little iron. Its specific gravity is 2585.