Geologists call this uniformitarianism. The physical laws governing the universe operate uniformly through time. See Levin, 5th edition, p. 10. The geologic record consists of rock units , each of which records some event or series of events that occurred in the past. Rocks are defined as aggregates of one or more minerals.
Most sedimentary rocks occur in the form of layers called beds or strata .
A. Steno's Laws Named for Nicholaus Steno, a Danish physician living in Florence, Italy in the 1600's. Levin, 5th edition, p. 6-8. The intrusion is younger than the rocks it cuts. The fault is younger than the rocks it cuts. Note the irregular erosional surface.