Cross dating chart. (Heather Hembrey, University of Maryland)
Cross-dating is a technique used to relatively date objects based on consistencies in stratigraphy between parts of a site or different sites, and objects or strata with a known relative chronology. A stratum containing artifacts that were originally deposited across the area at the same level may, over time, end up at different levels below the ground surface due to disturbances. Cross-dating allows archeologists to compare soil characteristics and artifacts within each stratum to determine their relationship relative to each other.
Try it yourself
View a movie about how archeologists use cross-dating.