ABSTRACT
Stratigraphy is the study of the origin, physical char-acteristics, and spatial relationships of stratified rocks, primarily to understand the history of events documented in the strata. Layers of sediment are the principal object of study, but layered volcanic rocks, and even metamorphosed strata, can also be interpreted according to the three great principles of stratigraphy. The principle of superposition states that in an undisturbed sequence each stratum is younger than the one beneath; the principle of original horizontality states that strata are horizontal or nearly so when they are deposited; and the principle of original lateral continuity states that all parts of a stratum, however disrupted by later activity, were once joined in a single connected layer.
