Principle of
 Superposition:

In a vertical sequence of undisturbed sedimentary layers or lava flows, the oldest layers are at the bottom, the youngest at the top.



 

Principle of
Horizontality:

Layers of sediments when originally deposited are fairly horizontal. Deformed rocks (folded or tilted) are therefore a consequence of deformation that postdates deposition.

1
This rock was folded after its deposition.
2
This deposition of the horizontal layers above the folded layers must be younger than the folding event.


 

Principle of Inclusions:

If an igneous intrusion (granite) contains fragments or inclusions of another rock, the inclusion must be older than the intrusion.

Inclusion
Inclusion of an older pre-existing rock within a younger light colored igneous intrusion.

 

Contact Metamorphism:

A hot intrusion of magma “bakes” a relatively cooler surrounding country rock. The rock that is baked during this process of Contact Metamorphism, must be older.


 

Principle of
Cross-Cutting Relations:

If one geological feature cuts across another, the feature that has been cut, is older.

Here all rock types are cut across by an intrusion of a dark colored igneous rock formation called dyke, thus it is the youngest feature.

An Earth Scientist sees 5 stages of geological events from the oldest event (1) to the relatively youngest event (5).

 

1
Deposition of sediments
2
Folding of sedimentary rock
3
Deposition of sediment and formation of secondary rock
4
Intrusion of light colour rock
5
Intrusion of dark colour dyke