Principle of Original Horizontality

The principle that layers of sediment are originally deposited horizontally under the action of gravity, first proposed by the Danish geological pioneer Nicholas Steno. It underpins the analysis of folded and tilted strata, from which follows the conclusion that great forces have moved Earth's crust over long periods; it is now known that some sediments, such as dune sands, are deposited at angles up to about fifteen degrees, so the principle is widely but not universally applicable. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/