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STRATIGRAPHY is the study of the layers of matrices and features. This STRATIFICATION is used as a relative dating system and is relieable due to the geological LAW OF SUPERPOSITION. This law states that events that occur and produce discards early in the history of the soil sample tend to be on the bottom, and later events and discards appear above this first layer, or STRATA. This means that if an archaeologist takes a coring sample to a depth of three feet, the material found at the bottom of the sample is generally older than that found at the top. Also generally, the material found 60% of the way down is older than that 50% down the length of the core.

However, please note one thing: the law of superposition refers only indirectly to the age of materials. We make this indirect connection ourselves based on the direct information given us through the law of superposition. The law tells us for a certainty that the lowest layers of a sample were DEPOSITED before the above layers. Because of the natural accumulation that occurs then, we ASSUME that these layers are older. And generally, they are.

However, there are exceptions to this rule. If a sample is taken from the mouth of a river, the stratigraphy might not be as we expect it; they layers may appear out of order. This is because that, as said above, stratigraphy reflects order of deposition, not age. At the mouth of the river, two types of deposits are made simultaneously. One type contains the fishhooks, oars, spearpoints, or whatever was being used immediately above that area. The other type of deposit includes anything that washed down stream, perhaps taking years to do so. Because of this, something discarded in, say 1566 and washed down