Originally posted by Flavian

Thank you for the response. Now i actually think about it, it seems obvious! Makes me wonder though how many sites have been "misread" over the years by people not properly taking things into account.

South America must be a nightmare for that. We see with the favellas in Brazil just how quickly different layers of the sub strata are exposed though top soil erosion (where trees have been removed owing to population). With such huge variety in South America, is must be a blooming nightmare working out the topograhpy and erosion rates before even getting on to any actual archeology!

Excavation Levels

Archaeologists do not excavate each unit in its entirety, and excavation proceeds by systematic levels or depth intervals. Four different methods include:

Natural or Stratigraphic Levels: Excavation reverses the natural order of deposition at a site by proceeding downwards one stratum at a time. Soil color, texture, and content are used to define different depositional levels.

Contoured Arbitrary Levels: The archaeologist picks an arbitrary depth (5 cm, 10 cm, etc.) to which the entire unit is excavated, paralleling the natural slope of the ground surface.

Simple Arbitrary Levels: Levels are defined by arbitrary depths below datum. When a level is completed, all four corners and the center of the unit will be the same depth below datum.

Combined Natural and Arbitrary Levels. Using both natural and arbitrary levels can be a flexible and practical method depending on the stratigraphic levels present in the unit.

A Constant Volume Sample (CVS) will be taken for every level excavated at the site. A CVS enables archaeologists to find tiny artifacts (e.g., flakes, fish bones, seeds) that would normally pass through the 1/8-inch mesh used for screening.