Flexi Says: Steno’s laws are sensible ideas about how sedimentary processes work; e.g. the rock on the bottom is the oldest. Using these laws makes it easier to determine in what order geological events happened. Rock layers extend laterally, or out to the sides. They may cover very broad areas, especially if they formed at the bottom of ancient seas. Erosion may have worn away some of the rock, but layers on either side of eroded areas will still “match up.” The Grand Canyon (Figure below) is a good example of lateral continuity.