A dome-shaped rock outcrop more than 30 m high, and sometimes several hundred metres in width, commonly rising above erosional plains in the tropics, but also found in unglaciated uplands in high latitudes. The origin of these features is problematic: faulting, lithological control, cross folding, and contrasts in fracture density have been cited. C. Twidale and J. R. Vidal Romaní (2005) give an excellent summary.