Unlike relative time, absolute time assigns specific ages to events or formations and is typically recorded in years before present.
Strata X to Z were laid down horizontally on top of the older beds.
The plane or junction, marked by the thick green line, between both sets of strata is the unconformity.
At Thornton Force the junction is marked by a basal conglomerate.
The most obvious feature of sedimentary rock is its layering.
This feature is produced by changes in deposition over time.
Techniques of accurately dating rocks is crucial in establishing the time-gap that exists.