What are the Principles of Relative Geologic Age Determination?
• The principle of original horizontality – sedimentary strata are initially deposited as horizontal or nearly horizontal layers. Note: If sedimentary strata dip at an angle other than horizontal, or are folded into various angles of tilt, then the layers of rock have been tilted or folded after the layers originally formed. • The principle of lateral continuity – sedimentary strata extend sideways for some distance. Note: If a sedimentary stratum occurs on one side of a stream valley and a seemingly identical stratum occurs at a corresponding level on the other side of the valley, then presumably they were once a single, laterally continuous layer that was later partly eroded away as the valley was eroded. • The principle of superposition – In a sequence of sedimentary strata, the stratum that is underneath is older, the stratum that is on top is younger. Note: This is probably the simplest and yet most powerful principle of relative age determination. However, to make sure it correct
