For purposes of relative dating this principle is used to identify faults and erosional features within the rock record.
Then, by applying the Principle of Cross-Cutting we are able to relatively date those processes.
Two broad categories of classification methods are relative dating and absolute dating.
It implies that relative dating cannot say conclusively about the true age of an artifact.
Absolute dating, on the other hand is capable of telling the exact age of an item using carbon dating and many other techniques that were not there in earlier times.
In order for any material to be included within in the rock it must have been present at the time the rock was lithified.
For example, in order to get a pebble inside an igneous rock it must be incorporated when the igneous rock is still molten-- such as when lava flows over the surface.
If conditions are right the remains of the dying organisms can then be preserved as fossils within the rock that formed from sediments that covered the remains.
Since, all sedimentary rock is formed through the gradual accumulation of sediment at the surface over time, and since the principle of superposition tells us that newer sediment is deposited on top of older sediment, the same must also be true for fossils contained within the sediment.
This means that the oldest are the strata that are lying at the bottom.
However, age of deposition does not mean the age of artifacts found in that layer.
The principle of cross-cutting states that any geologic feature that crosses other layers or rock must be younger then the material it cuts across.
Using this principle any fault or igneous intrusion must be younger than all material it or layers it crosses.
The Principle of Original Horizontality states that due to the influence of gravity all sediment is originally deposited horizontally.