Those who study the earth’s crust—its origin, history, rocks, minerals,
fossils, and structure—are known as _geologists_. The geologists who are
especially interested in a particular phase of _geology_, as this
science is called, are given special names: those who study fossils are
called _paleontologists_; those who study minerals are called
_mineralogists_; those who study rocks are called _petrologists_.