Strata with Fault Line
An illustration of strata bent at a line of fault. In geology and related fields, a stratum (plural: strata) is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural forces.
Encyclopaedia Britannica (11th ed., vol. 10) (New York, NY: The Encyclopaedia Britannica Company, 1910)