Hitherto, the quarry masons had always hewn stone roughly, providing blocks of varying size. Wood required stone blocks to be cut with crisp clean edges for his distinctive classical façades. The stone was extracted by the "room and pillar" method, by which chambers were dug out, leaving pillars of stone to support the roof. Bath stone is an Oolitic limestone comprising granular fragments of calcium carbonate laid down during the Jurassic period (195 to 135 million years ago). An important feature of Bath stone is that it is a freestone, that is one that can be sawn or 'squared up' in any direction, unlike other rocks such as slate, which has distinct layers. It was extensively used in the Roman and Medieval periods on domestic, ecclesiastical and civil engineering projects such as bridges.