Two types of stone were used in the tower: whitish to pinkish Triassic sandstone and dark-grey dolerite. The sandstone, more suitable for fine carvings, was used for quoins, window dressings, stairs, corbels, copings and roofs, as well as for courses that mark limits: the moulding between the base and the main body and the one that separates the stair tower from the cap-house above it. The dolerite is described as whinstone or as basalt in various sources. This material is harder and more resistant to weathering than the sandstone but difficult to work. It was cut into blocks of variable size and laid in frequently interrupted courses. The outer surfaces of these blocks were left in rough rustication with many blocks quite prominent.