Distribution of Rock Types
Of these three rock types, the most common near the surface of the crust is sedimentary rock. This is due to the many rivers, lakes, and seas that have covered the surface at one time or another. This layer of sedimentary rock is very thin, however, extending downward only a mile or so in depth. Below this sedimentary rock and also mixed with it in many locations is igneous rock.
The bulk of the Earth’s crust is made up of both igneous rock and metamorphic rock.