The Ground Is an Archive
Dirt is a dated document. Superposition states that in undisturbed deposits, lower layers are older, making depth a relative clock. A site is recorded through the context: a single depositional event.
| Principle | Statement | Consequence |
|---|---|---|
| Superposition | Lower layers are older | Depth is a relative clock |
| Cutting | Cuts are younger than what they cut | Intrusions date after targets |
| Filling | Fills are younger than their cut | Contents postdate the pit |
| Association | Sealed objects entered together | Context is the dating unit |
The Harris matrix diagrams these older/younger relationships as a flowchart of time, separating stratigraphy from soil.
Termini and Pitfalls
Objects bracket layer ages from one side only.
- Terminus post quem (TPQ): limit after which. A coin from 120 CE inside a fill means the fill closed no earlier than 120.
- Terminus ante quem (TAQ): limit before which. Structures sealed beneath datable layers are older.
Residuality is the classic trap: old things constantly end up in young layers. The latest object sets a context's TPQ. The section shows where things are, but sequence is the true clock.