The Ordovician time period lasted from 505
to 440 million years ago, a time span of 65 million years. The term Ordovician
was first used in the 1870s to describe a sequence of rocks in Wales.
The name Ordovician was derived from the name of an ancient British tribe.
These Ordovician rocks were defined based on a particular type of fossil
assemblage contained within them. They are located above the rocks of
the Cambrian System and below the rocks of
the Silurian System.