Stratigraphy

Stratigraphy is the study of geological and archaeological strata on a site. The purpose of stratigraphical analysis is to isolate and date different occupation levels or building phases, distinguishing them from natural or geological layers. Each stratum is called "a stratigraphical unit" (S.U.), and each S.U. is given a unique number in the site's database. The date of a S.U. is always relative to the other units on a site (deeper implies older) and can sometimes also be absolute, if the unit contains precisely datable material (e.g., a coin).