by the removal of, a pre-existing mass of archaeological stratification. The principle that layers can be no older than the age of the most recent artefact discovered within them. This is the basis for the relative dating of layers using artefact typologies. It is analogous to the geological principle of faunal succession, although Harris argued that it was not strictly applicable to archaeology. He also proposed three additional principles: The principle of original horizontality states that any archaeological layer deposited in an unconsolidated form will tend towards a horizontal deposition. Strata which are found with tilted surfaces were so originally deposited, or lie in conformity with the contours of a pre-existing basin of deposition. The principle of lateral continuity states that any archaeological deposit, as originally laid down, will be bounded by the edge of the basin of deposition, or will thin down to a feather edge. Therefore, if any edge of the deposit is exposed in a vertical plane view, a part of its original extent must have been removed by excavation or erosion: its continuity must be sought, or its absence explained. The principle of stratigraphic succession states that any given unit of archaeological stratification exists within the stratigraphic sequence from its position between the undermost of all higher units and the uppermost of all lower units and with which it has a physical contact. Combining stratigraphic contexts for interpretation Understanding a site in modern archaeology is a process of grouping single contexts together in ever larger groups by virtue of their relationships. The terminology of these larger clusters varies depending on the practitioner, but the terms interface, sub-group, and group are common. An example of a sub-group could be the three contexts that make up a burial; the grave cut, the body, and the back-filled earth on top of the body. Sub-groups can then be clustered together with other sub-groups by virtue of their stratigraphic relationship to form groups, which in turn form "phases." A sub-group burial could cluster with other sub-group burials to form a cemetery, which in turn could be grouped with a building, such as a church, to produce a "phase". Phase implies a nearly contemporaneous Archaeological horizon, representing "what you would see if you went back to time X".The production of phase interpretations is the first goal of stratigraphic interpretation and excavation. Stratigraphic dating Archaeologists investigating a site may wish to date the