Archaeological Stratigraphy: The Law of Superposition

Excavation Trench

Soil layers 6

Include a burial-pit intrusion Auto-rotate camera

Dig Progress

Excavated

0 / 6

Now exposed at surface

—

Artifacts recovered

Click "Excavate next" to begin the dig.

How it works

Law of Superposition (Nicolas Steno, 1669): in an undisturbed sequence of horizontal deposits, each layer is younger than the layer beneath it and older than the layer above it. So relative age = vertical position — no lab test needed, just careful digging from the top down.

Undisturbed stack, bottom → top:
  Layer 0 (bedrock)  → oldest
  Layer 1
  ...
  Layer N-1 (topsoil) → youngest

Principle of Cross-Cutting Relations: a feature that cuts through existing layers — a pit, ditch, post-hole, or burial — is always younger than the youngest layer it cuts, no matter how deep it reaches. That's why the pit in this trench is excavated first, even though its fill descends through several "older-looking" layers.

Harris Matrix: archaeologists formalize both rules as a directed graph of "unit A is stratigraphically above/later than unit B" relationships, built purely from what physically touches what — the same logic this dig enforces by only letting you remove the topmost exposed unit at each step.

Soil layers — sets how many deposits (5–8) make up the sequence.
Burial-pit intrusion — toggles a later feature dug down through the upper layers, with its own grave good.
Excavate next — removes only the currently topmost unit, exactly as real stratigraphic excavation requires.

Artifact still buried Artifact exposed Pit fill (intrusion)

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