Cross-cutting relationships dictate that geologic features cutting across strata are younger than the rocks they cut.
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Reference documentation and geological guides confirm that the principle of cross-cutting relationships establishes that any geologic feature cutting across strata or rock structures is younger than the rocks it cuts.
Cross-cutting relationships
Cross-cutting relationships can be used to determine the relative ages of rock strata and other structures. Explanations: A – folded rock strata cut by a thrust fault; B – large intrusion(cutting through A); C – erosional angular unconformity(cutting off A & B) on which rock strata were deposited; D – volcanic dike(cutting through A, B & C); E – even younger rock strata (overlying C & D); F – normal fault(cutting through A, B, C & possibly E).
Cross-cutting relationships is a principle of geology that states that the geologic feature which cuts another is the younger of the two features. It is a relative dating technique in geology. It was first developed by Danish geological pioneer Nicholas Steno in Dissertationis prodromus (1669) and later formulated by James Hutton in Theory of the Earth(1795) and embellished upon by Charles Lyell in Principles of Geology(1830).
## Types
There are several basic types of cross-cutting relationships:
- Structural relationships may be faults or fractures cutting through an older rock.
- Intrusional relationships occur when an igneous pluton or dike is intruded into pre-existing rocks.
- Stratigraphic relationships
Fossils, Rocks, and Time: The Laws of Superposition and Cross-Cutting Relations
## THE LAWS OF SUPERPOSITION AND CROSS-CUTTING RELATIONS
The basalt flow shown here obeys the Law of Superposition. It is younger than the beds below it and older than the beds above it. Note that the molten rock of the volcanic flow has baked the rock underneath it. The bed above was deposited long after the flow had cooled and hardened and has not been baked. Numeric ages from the flow and dike and relative ages from the fossils in the surrounding rocks contribute to the geologic time scale.
| The granite dike (a mass of rock that cuts across the structure of the rocks around it) shown here illustrates the Law of Cross-Cutting Relations. The dike is younger than all the rocks that it cuts across and older than the rocks above it that it does not cut. Note that the contact between the dike and the rocks around it has been baked by the heat of the molten granite. |
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Return to The Numeric Time Scale
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This page is URL: https://pubs.usgs.gov/gip/fossils/laws.html Last updated 26 June 1997 (krw) Maintained by John Watson
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