These layers of sedimentary rock were deposited in Cambrian ... At the very bottom of the canyon lies the Vishnu Schist, a hard rock originally deposited mainly as sediments some 2 billion years ...

The only exception to the rule is Country Tyrone which has a bit of everything - clay, basalt, gabbro, granite, schist ... to form a new type of rock called sedimentary rock.

There are three main types of rock — igneous, sedimentary and metamorphic ... with examples including phyllite, schist, quartzite and marble. Igneous and metamorphic rocks on Earth's surface ...