Stratigraphy is the branch of geology which studies rock layers (strata)
and layering (stratification).Stratigraphy deals primarily with
sedimentary rocks but also embraces layered igneous rocks where layers
result from successive lava flows.A common goal of stratigraphic studies
is the interpretation of sequences of rock strata, thus understanding
the time relationships involved, and correlating units of the sequence
with rock strata elsewhere. Nicholas Steno described four principles of
stratigraphy in the seventeenth century, including the law of
superposition which states that states that, in undeformed stratigraphic
sequences, the oldest strata will be at the bottom of the sequence.
These ideas still underpin modern stratigraphy which is governed by The
International Commission on Stratigraphy. Its primary objective is to
precisely define global units (systems, series, and stages) of the
International Chronostratigraphic Chart that, in turn, are the basis for
the units (periods, epochs, and age) of the International Geologic Time
Scale.Stratigraphy has application in many scientific fields, including
archaeology, palaeontology and in the search for natural resources. This
succinct and accessible introduction to stratigraphy will prove helpful
to students and amateur geologists alike.