( 3*5 ) TWELFTH SPECIES. Polier, or Polifhing Slate. Polierfchiefer.—Werner. External Chambers. ' Its colour is yellowifh grey, which approaches to fcream yellow and yellowifh white. It is always ftriped, and the colours alternate in layers. Occurs only maflive. > Internally it is dull. Its principal frafture is flaty, the crofs figure earthy. Fragments generally tabular. Very foft paffing into foft. Adheres to the tongue. Feels fine but meagre. Not particularly heavy, approaching to light, even Nearly fwimming. It is lighter than tripoli. Ceognostk