The principle of lateral continuity states that layers of

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

initially extend laterally in all directions; in other words, they are laterally continuous. As a result, rocks that are otherwise similar, but are now separated by a

valley A valley is an elongated low area often running between Hill, hills or Mountain, mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers ...

or other

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

al feature, can be assumed to be originally continuous. Layers of sediment do not extend indefinitely; rather, the limits can be recognized and are controlled by the amount and type of sediment available and the size and shape of the

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subsidence ...

. As long as sediment is

transported ''Transported'' is an Australian convict melodrama film directed by W. J. Lincoln. It is considered a lost film. Plot In England, Jessie Grey is about to marry Leonard Lincoln but the evil Harold Hawk tries to force her to marry him and she w ...

to an area, it will eventually be deposited. However, as the amount of material lessens away from the source, the layer of that material will become thinner. Often, coarser-grained material can no longer be transported to an area because the transporting medium has insufficient energy to carry it to that location. In its place, the particles that settle from the transporting medium will be finer-grained, and there will be a lateral transition from coarser- to finer-grained material. The lateral variation in sediment within a

stratum In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

is known as

sedimentary facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

. If sufficient sedimentary material is available, it will be deposited up to the limits of the sedimentary basin. Often, the sedimentary basin is within rocks that are very different from the sediments that are being deposited. In those cases, the lateral limits of the sedimentary layer will be marked by an abrupt change in rock type.

References

{{Geologic Principles Stratigraphy he:עקרון הסופרפוזיציה (גאולוגיה)#עקרון ההמשכיות האופקית