Which principle applies to sedimentary layers that are laid down level on top of each other?

The principle that applies to sedimentary layers laid down level on top of each other is the Law of Original Horizontality. This principle states that layers of sediment are originally deposited in a horizontal position due to the influence of gravity. If sedimentary layers are found tilted or folded, it indicates that geological processes, such as tectonic activity, occurred after their deposition.