<p>Basically a formation is just a layer or group of layers of rock that is both distinct enough to be identifiable in the field and large enough to show up on a geological map. Usually it is many nearly identical layers grouped together or just one large layer. Its not a hugely precise definition but it is a lot like the term "species" in biology, it's a working definition, created more for usability than precision.    </p>

CC BY-SA 3.0
2017-02-27T15:45:44.307Z
2017-02-27T15:45:44.307Z
John
<p>According to Wikipedia, and perfectly consistent with basic historical geological textbooks, a formation is:</p>

<p><a href="https://en.wikipedia.org/wiki/Geological_formation" rel="nofollow noreferrer"><strong>...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. ... The concept of formally defined layers or strata is central to the geologic discipline of stratigraphy.</strong></a></p>

<p><a href="https://i.sstatic.net/dhwZU.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/dhwZU.jpg" alt="A geologic cross section of the Grand Canyon. Black numbers correspond to groups of formations and white numbers correspond to formations."></a></p>

<p><a href="https://en.wikipedia.org/wiki/Geological_formation" rel="nofollow noreferrer"><strong>A geologic cross section of the Grand Canyon. Black numbers correspond to groups of formations and white numbers correspond to formations.</strong></a></p>

<p>Typically, formations are traceable across some distance.</p>

CC BY-SA 3.0
2017-02-26T19:01:24.353Z
2017-02-26T19:01:24.353Z
Knob Scratcher
<p>Geology: What's make a group of bed a formation?</p>

<geology><bedrock>
Geology: What's make a group of bedrock a formation?
Alvaro Morales
# Geology: What's make a group of bedrock a formation?

(Asked by: username_0 on 2017-02-26)

Geology: What's make a group of bed a formation?

**Tags:** geology, bedrock


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## 2 answers

### Answer by username_1 on 2017-02-27. Score: 5

Basically a formation is just a layer or group of layers of rock that is both distinct enough to be identifiable in the field and large enough to show up on a geological map. Usually it is many nearly identical layers grouped together or just one large layer. Its not a hugely precise definition but it is a lot like the term "species" in biology, it's a working definition, created more for usability than precision.


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### Answer by username_2 on 2017-02-26. Score: 2

According to Wikipedia, and perfectly consistent with basic historical geological textbooks, a 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. ... The concept of formally defined layers or strata is central to the geologic discipline of stratigraphy.**](https://en.wikipedia.org/wiki/Geological_formation)

[![A geologic cross section of the Grand Canyon. Black numbers correspond to groups of formations and white numbers correspond to formations.](https://i.sstatic.net/dhwZU.jpg)](https://i.sstatic.net/dhwZU.jpg)

[**A geologic cross section of the Grand Canyon. Black numbers correspond to groups of formations and white numbers correspond to formations.**](https://en.wikipedia.org/wiki/Geological_formation)

Typically, formations are traceable across some distance.


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