Diviners are essential figures in many African religious traditions because they are often employed to counter witches. The Dogon cosmogony is evident in its social and village structures. In contrast to the Dogon worldview, the Zulu of Southern Africa conceive of the sky as a blue rock and the earth with a flat surface. In African religious cultures, time tends to be conceived as local and fore-shortened, suggesting that it is more microcosmic than macrocosmic. Some African cultures have another category of spirits that can be called the living dead, who are deceased members representing five generations. Ancestor worship is socially grounded in domestic, kinship-descent relations and institutions of a culture. The ritual process of a society often includes or presupposes a process of purification, which is necessary before one can engage in a sacrifice.