How could a geologist match the rock layers in one area to rock layers found in another area

By looking at similarities like the composition, sequences and Index Fossils if present

Explanation:

To correctly match a certain Rock layer with another the geologist use different methods to find the similarities of a rock layer in an outcrop between them. The first step is to determine the characteristics of the rock layers, and the sequence, depending on the types of rock and their shape, for example, a rock layer can be a Gneiss, Basalt, Sandstone, etc.

In case Index Fossils are found the geologist correlates them with a certain geology period, For example, a trilobite would be related to a Devonian Period.

With these data, the geologist compares the structure and similar formations characteristics found in outcrops and the possible Age of the rock layers with the Index fossils.