There may be a layer missing in the strata, or a set of sedimentary rock on top of metamorphic rock.These interfaces between discontinuous layers of rock are called unconformities.How do we use the Law of Superposition to establish relative dates?
Geologists use this type of method all the time to establish relative ages of rocks.
Now, what if instead of being horizontal, this rock layer was found in a tilted position?
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.
Geologists find the cross-cutting principle especially useful for establishing the relative ages of faults and igneous intrusions in sedimentary rocks.
Sometimes, geologists find strange things inside the strata, like chunks of metamorphic or igneous rock.If it had happened before the layers had formed, then we wouldn't see it punching through all the layers; we would only see it going through the layers that had existed at the time that it happened. The Principle of Cross-Cutting Relationships states that rock formations that cut across other rocks must be younger than the rocks that they cut across.The same idea applies to fault lines that slide rock layers apart from each other; a fault that cuts across a set of strata must have occurred after the formation of that set.Since we assume all the layers were originally horizontal, then anything that made them not horizontal had to have happened after the fact.We follow this same idea, with a few variations, when we talk about cross-cutting relationships in rock.What could a geologist say about that section of rock?