Mary Leakey Quote

Archaeologists often divide things into three stages, usually 'lower', 'middle' and upper' if they are thinking stratigraphically. Afterwards, of course, they argue that the whole thing was continuous anyhow and that the divisions are arbitrary and for convenience only.

Disclosing the Past: An Autobiography - By way of prelude (p. 13), Doubleday & Company, Inc. 1984