The vertical distance measured from the base to the top of a stratigraphic unit or archaeological layer, expressed in linear units and referenced to a specified local vertical datum; it records the layer's present vertical extent at the point of measurement.

Principle

Measured thickness, when combined with plan measurements, determines the unit's contribution to deposited volume; because thickness commonly varies across a unit, representative sampling or integration is required for volumetric estimates.

Demonstration

Illustrative scenario — Situation: In a trench, the recorded top of Layer A is 0.30 m below the site datum and the base is 1.20 m below datum. Recognition: The archaeologist identifies a coherent layer bounded by those surfaces. Action: Compute thickness = base depth − top depth = 1.20 m − 0.30 m = 0.90 m. Consequence: That thickness value enters calculations of Layer A's volume when multiplied by its plan area or used in three‑dimensional models.

Misapplication

Treating a single point measurement as the layer's uniform thickness across the site; this ignores lateral variation and can misestimate volume and deposition history.

Consequence

An inaccurate thickness estimate causes proportional errors in volume calculations, artifact density estimates, and interpretations of depositional rate or sequence; those downstream analyses therefore depend on explicit sampling strategy and datum.

Reversal

When strata are tilted, folded, or laterally truncated, vertical thickness (measured parallel to the site vertical) differs from geological 'true thickness' measured perpendicular to bedding; in those conditions vertical measurement may not represent original depositional thickness.

Boundary

Clearly within: a horizontally bedded occupation deposit with consistent top and base in a trench. Boundary case: an irregular lens whose top and base pinch out rapidly across short distances. Clearly outside: a point elevation measurement (datum) or the depth to an isolated artifact unrelated to a defined stratigraphic unit.

Semantic Tension

Practical vertical measurement (ease, archaeological convention) ↔ geological accuracy of true (perpendicular) thickness when structural deformation exists.

Synthesis

Stratigraphic thickness is an operational, datum‑dependent measurement whose interpretive value requires explicit recording of reference surface, sampling locations, and awareness of lateral variability and post‑depositional deformation.