Relative dating cannot establish absolute age, but it can establish whether one rock is older or younger than another.
Relative dating requires an extensive knowledge of stratigraphic succession, a fancy term for the way rock strata are built up and changed by geologic processes.
Techniques of accurately dating rocks is crucial in establishing the time-gap that exists.
The classic type is the angular unconformity of which Thornton Force in Ingleton and Combs Quarry, Foredale are perhaps the best known local examples.
The geologic timescale is a chronology (calendar) of events on Earth based on obtaining ages of past events.It's called the Principle of Original Horizontality, and it just means what it sounds like: that all rock layers were originally horizontal. As you can imagine, regular sediments, like sand, silt, and clay, tend to accumulate over a wide area with a generally consistent thickness.It sounds like common sense to you and me, but geologists have to define the Principle of Original Horizontality in order to make assumptions about the relative ages of sedimentary rocks. Say you have a layer of mud accumulating at the bottom of a lake. More sediment accumulates from the leaf litter and waste of the forest, until you have a second layer.This is shown below: The Angular Unconformity The strata A to E was deposited first, tilted, subjected to erosion (peneplained) and submerged.Strata X to Z were laid down horizontally on top of the older beds.