The layer of soil which contains the byproducts of human activity as the result of the accumulation of these materials on their living surface. For prehistoric sites, a layer of soil that was stained to a dark color by the decomposition of organic refuse which also contained food bones, fragments of stone tools, charcoal, pieces of pottery, or other discarded materials. For historic sites, a similar layer of soil but with appropriate historic material remains often in a much thinner deposit.