Geologic Formations
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties. Formations are not defined on the thickness of the rock strata they consist of and the thickness of different formations can therefore vary widely.
The concept of formally defined layers or strata is central to the geologic discipline of stratigraphy. A formation can be divided into members and are themselves grouped together in groups.
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