Form of lignite, black and consisting largely of carbon. It is driftwood from pines related to the Araucaria genus (monkey-puzzle tree) that has been subjected to chemical action in stagnant water and then to great pressure in the ocean floor. It is found in the bituminous shales of the Upper Lias, which was laid down about 170 million years ago, and occurs in the form of horizontal wedge-shaped strata up to 400 mm wide, 150 mm long and 100 mm deep. Sometimes it is washed up on beaches as pebbles. The best jet is found in England, at Whitby (N. Yorks), and the only other major deposits are in northern Spain in the Asturias. Lesser deposits have been found in France, Germany, the Czech Republic, Slovakia, Italy, Portugal, Canada and the USA.