Law of Horizontality in Sediments
Sedimentary Rock Processes

Nicholas Steno

The Law of Original Horizontality was first proposed by Danish geological pioneer Nicholas Steno in the 17th century. The law states that layers of sediment were originally deposited horizontally under the action of gravity. Any rock layers that are now folded and tilted have since been altered by later outside forces. This is a fundamental law in geology and especially important for the understanding of plate tectonics.