STRATIGRAPHY is a branch of science which may be de fined as the study of the relative position and order of succes sion of deposits containing or separating archaeological material.
Stratified deposits may be classified under (r) Archaeological, (2) Archaeological and Geological, (3) Geological.
(I) A purely artificial accumulation, as on a town or settle ment site of historic or comparatively late prehistoric age. The section through the Temple of Artemis Orthia at Sparta is a fine example of stratigraphical work yielding chronological informa tion covering at least 1,000 years. Study of this section shows the older deposits divided from the newer by a sand stratum. The lower levels dated by their respective potteries, cover the period of an early temple represented by an altar and walls. The sacrificial deposits are of unequal thickness on both sides of the altar, indicating that one side was kept clear for officiation. The altar was therefore in existence while the surrounding strata were accumulating. Contrasted with this is the uniformity of level near the walls, showing that these are more recent than the deposits through which they were cut. This early temple appears to have been destroyed by flood, and our next period belongs to rebuild ing in the 6th century B.C. The site was artificially levelled up by a sand deposit of 12 metres thick in order to raise the new temple above flood level. The Greek altar and associated deposits belong to this period. This building remained in use until a Hellenistic reconstruction about i 78 B.C. The Roman period is superimposed, beginning about 35o years later. Inscriptions, ranging from the 4th century B.C. to A.D. 225 built into the foundations of the theatre prove that it can hardly be earlier than A.D. 250, since a stele is unlikely to have been thrown aside less than 25 years after its erection.
(2) A combination of natural and artificial conditions, best exemplified by cave deposits, showing strata of early human occu pation, interbedded with strata of geological formation such as stalagmitic floor, or flood-borne silt. Caves and rock-shelters were primitive man's abode both before, during, and after the last great ice-age. Here he left his flint and bone implements, his hearths and the bones of wild beasts killed for food, unconsciously build ing up over a period of many thousand years, in conjunction with geological agencies, a stratigraphy as certain as a town mound.
Cave deposits may attain a vertical depth of 45ft. The inequal ities of a cave floor render it improbable that the superimposed deposits will be horizontal or evenly distributed. In many cases one well-defined stratum of a series may contain relics of more than one period, and the level in it, at which archaeological change becomes apparent, may be missed unless suitably fine horizontal sub-divisions are made by the excavator.
In the section through the Rock Shelter at Laussel, S. France, we have strata tilting and overlapping. The oldest deposits of lower and middle palaeolithic age lie some distance from the sheltering cliff. There follows a long interval when the site was abandoned and cliff detritus and humus raised the level. Upper palaeolithic man returned and resumed discontinuous occupation. Deposits cover probably a period of at least 25,00o years. The section illustrates the confusion in interpretation of sequence which would result from unsuitable methods of excavation.
(3) Stratigraphical conditions fall within the domain of archae ology. There comes, however, a point at the beginning of the human record when archaeological stratigraphy merges into pure geology. River-terrace gravels illustrate this category. The major river valleys frequently show old terraces of sand and gravel at various heights above the present stream. These mark former levels. In many cases these old terraces contain fossil animal re mains and palaeolithic flint implements of different ages. In the case of river gravels, however, the usual law of stratigraphical sequence as shown in (I) and (2) is inverted ; the highest terrace will normally (though not invariably) have been deposited first, and will contain the oldest material, whilst the formation of the lower terraces will be episodes in the later degradation of the river bed. Material from the older deposits may consequently be washed into the later ones ; the true age of an alluvial deposit is that of its most recent content.
The section of the Somme near St. Acheul, France, shows that river gravel stratigraphy is rendered additionally complex by over-lying deposits of later date covering older and younger ter races which contain in their turn archaeological material.
See J. P. Droop, Archaeological Excavations (1906). (G. C.-T.)