The artifacts are placed in a bag marked with the grid coordinates and the layer number. The exact location where the artifacts are found is called the provenience. Each layer represents a segment of time, much like a timeline. Archaeologists also encounter features while they are digging. Features are areas which appear different from the surrounding soil because the ground was disturbed in the past.
Features are usually the result of human activity.
Some examples of features are building foundations, abandoned wells and privies, trash pits and burials. Usually the lowest layers are the earliest, although features such as wells, foundations and post-holes may have been dug through earlier layers. Archaeological excavation techniques are tailored to the individual site. In some circumstances, such as in the excavation of some wells, stratigraphic layers cannot be identified by soil color and consistency. When strata are either indistinguishable or very deep, arbitrary levels are defined by the archaeologist.