exposed rock mass of jointed and broken blocks. Tors are seldom more than 15 metres (50 feet) high and often occur as residues at the summits of inselbergs and at the highest points of pediments. Tors usually overlie unaltered bedrock and are thought to be formed either by freeze–thaw weathering or by groundwater weathering before exposure. There is often evidence of spheroidal weathering of the squared joint blocks.