Rocks and the rock cycle
Rock type records how the rock formed, and the rock cycle keeps turning each type into the others.
A worked example
A cliff face shows sandstone below shale below limestone. All three are sedimentary, and the sandstone at the bottom settled first.
The mistake people actually make
Metamorphic rock is changed by heat and pressure but never fully melts. Once it melts and cools it is igneous. Reading layers as a time sequence only works where they have not been folded or overturned.