Relative Time

principal of original horizontality

sediments are deposited as horizontal layers s

 Superposition

In an undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below

disconformity

an erosional surface between horizontal sedimentary rocks

matching of similarly-aged rocks from different outcrops

The study of fossil succession allows ___________ .

William Smith

fossil succession

nonconformity

a gap in the geologic record bounded below by metamorphic or igneous rocks and bounded above by sedimentary rocks

Uniformitarianism

“the present is the key to the past” (Hutton)

Lateral Continuity

Beds originate as continuous layers that extend in **all directions**

Nicolaus Steno

superposition

original horizontality

lateral continuity

Cross-Cutting Relations

Younger features cut across older features

Inclusions and Components

Fragments of rock that are within another rock are older