Geologic time relative age dating
He also found that certain animals were in only certain layers and that they were in the same layers all across England.
Due to that discovery, Smith was able to recognize the order that the rocks were formed.
A similar situation with igneous rocks occurs when xenoliths are found.
These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix.
The principle of inclusions and components states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them.
As he continued his job as a surveyor, he found the same patterns across England.however, this process is not enough to allow the layers to change their positions.This principle allows sedimentary layers to be viewed as a form of vertical time line, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed.Sixteen years after his discovery, he published a geological map of England showing the rocks of different geologic time eras.Methods for relative dating were developed when geology first emerged as a natural science in the 18th century.