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Horizontality – Steno also studied the landscape and how sediment settled in water. He realised sedimentary layers are deposited flat. Try mixing some fine dirt in a jar of water and watch how it settles. Now imagine this process at the scale of rivers, lakes and oceans, where sediment is carried by moving water. When the water slows, the sediment drops out and forms flat layers. But what if we see folded layers of rock or layers standing upright, or even tortured in all different directions? Because sediments always settle flat, this must have happened after the sediments were laid down! This is the law of original horizontality.