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The principle of original horizontality states that layers of 
From these observations is derived the conclusion that the Earth has not been static and that great forces have been at work over long periods of time, further leading to the conclusions of the science of plate tectonics; that movement and collisions of large plates of the Earth's crust is the cause of folded strata.
As one of Steno's Laws, the principle of original horizontality served well in the nascent days of geological science.Kardel, Troels, ed. (2013). Nicolaus Steno: Biography and Original Papers of a 17th Century Scientist. Berlin: Springer. ISBN 978-3-642-25078-1. However, it is now known that not all sedimentary layers are deposited purely horizontally. For instance, coarser grained sediments such as
{{DEFAULTSORT:Principle Of Original Horizontality
Stratigraphy
sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
are originally deposited horizontally under the action of gravity
In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...
. It is a relative dating technique. The principle is important to the analysis of folded and tilted strata
In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...
. It was first proposed by the Danish geological pioneer Nicholas Steno (1638–1686). From these observations is derived the conclusion that the Earth has not been static and that great forces have been at work over long periods of time, further leading to the conclusions of the science of plate tectonics; that movement and collisions of large plates of the Earth's crust is the cause of folded strata.
As one of Steno's Laws, the principle of original horizontality served well in the nascent days of geological science.Kardel, Troels, ed. (2013). Nicolaus Steno: Biography and Original Papers of a 17th Century Scientist. Berlin: Springer. ISBN 978-3-642-25078-1. However, it is now known that not all sedimentary layers are deposited purely horizontally. For instance, coarser grained sediments such as sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...
may be deposited at angles of up to 15 degrees, held up by the internal friction between grains which prevents them slumping to a lower angle without additional reworking or effort. This is known as the angle of repose, and a prime example is the surface of sand dunes.
Similarly, sediments may drape over a pre-existing inclined surface: these sediments are usually deposited conformably to the pre-existing surface. Also, sedimentary beds may pinch out along strike, implying that slight angles existed during their deposition. Thus the principle of original horizontality is widely, but not universally, applicable in the study of sedimentology, stratigraphy
Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithost ...
, and structural geology.See also
* Law of superposition * Principle of cross-cutting relationships * Principle of faunal succession * Principle of lateral continuityReferences
{{DEFAULTSORT:Principle Of Original Horizontality
Stratigraphy