Which principle is a geologist applying when deciding that a fossil in a mud layer is older than a fossil in a sandstone layer above it?

Question

Quizplus · Accepted Answer

The principle of superposition states that in an undisturbed sequence of sedimentary rocks, each layer is older than the one above it and younger than the one below it. Therefore, if a fossil is found in a mud layer below a sandstone layer, it must be older than the fossil found in the sandstone layer above it.

Which Principle Is a Geologist Applying When Deciding That a Fossil