Stratigraphy is a branch of geology which studies rock layers and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy includes two related subfields: lithologic stratigraphy or lithostratigraphy, and biologic stratigraphy or biostratigraphy.
Read more about Stratigraphy: Historical Development, Lithologic Stratigraphy, Biostratigraphy, Chronostratigraphy, Magnetostratigraphy, Archaeological Stratigraphy