A third possibility, is the strata of different levels of stone and clay according to my book.. the maze theory happened in the 1960s did'nt it, at the start of all things magical and mystical to do with prehistory and the world ;)
Anyway a Dugdale drawing (17th century) shows medieval ridge and furrow half way up the Tor, and then the lynchets. Its a fascinating thing if it did turn out to be a maze but I'm not convinced, the person who thought it was a maze took his template from Chartres cathedral which seems a bit dubious...