footholds were cut into the sides of the shaft to allow the miners to climb in and out. the shaft, when the chalk is reached, widens out into a domed chamber with a roof of chalk some 3 feet thick. the walls frequently contract somewhat as they near the floor. as a rule the main chamber is 16 to 18 feet in height, beneath each shaft. from this excessive height it has been inferred that the caves were not primarily intended for habitations or even hiding-places. in most cases, between two and four sub-chambers are present, excavated laterally from the floor level, the roof being supported by pillars of chalk left standing.