The Law of Original Horizontality is a geological principle that states that layers of sediment are originally deposited horizontally under the action of gravity. In simpler terms, when sedimentary rock forms, it starts out as flat, horizontal layers. This law is fundamental in the study of stratigraphy, which is the analysis of sedimentary rock layers.
When examining these layers, geologists can infer how they have been altered over time due to natural processes such as tectonic activity, erosion, or other geological forces. If sedimentary rock layers are found tilted or folded, it indicates that some geological event occurred after their deposition that caused these changes. Hence, by understanding the original horizontal position of sediment layers, geologists can reconstruct the geological history and events that shaped the landscape.