Stratigraphic section

Sequence of layers of rocks in the order they were deposited

A stratigraphic section is a sequence of layers of rocks in the order they were deposited. It is based on the principle of original horizontality, which states that layers of sediment are originally deposited horizontally under the action of gravity. Biostratigraphers estimate the age of stratigraphic sections by using the faunal assemblages contained within rock samples from outcrop and drill cores.

From Wikipedia, under CC BY-SA. More on occurri.