The deposit thus occurring forms layers depending on the nature of the material brought in by the people inhabiting the area.
This closely agrees with the fact that the seals from Indus Valley style from Ur, Kish and Tell Asmar and other sites fall within the range of 2500-1500 B. When a group or type of objects are found together under circumstances suggesting contemporanity they are said to be associated.
For example, beads closely resembling those from the temple repositories at Cnoss and dating from C.1600 B.
C were found in a late context (Period V) at Harappa. By noting the association of these beads it has been possible to trace a archaeological datum line across Indian sub-continent and Mesopotamia.
Basing on this principle, the cultural assemblages found in different layers can be assigned a chronological personality. In practice it is found that the mounds are disturbed9+ by all sorts of pits and dumps.
For example, if the cultural contents of the lower deposit are Mauryan in character, appropriately this deposit may be assigned a date between 400-200 B. Similarly, if the cultural equipment of the upper deposit are of the Sunga period, this deposit has to placed between 200-73 B. Quite often, the archaeologist decided the change of stratum on the basis of the feed of the deposit.
Even when the absolute dates are available, we have to supplement the information with relative dating.The various methods of relative dating are; This method depends on the common observation that the height of the habitational area increases as the people continue to live at the same place.This dating method is also known as Archaeological Dating or Historical Chronology. These methods were relied on especially prior to the introduction of scientific methods of dating.But, even when the scientific methods of absolute dating are available, this method of dating has not lost its importance, as many a time we have to depend solely on relative dating.In such cases subjective element cannot be ruled out.But, for a single culture site the method is quite reliable.