Geological Time - the Silurian Period
The geological timescale is defined using evidence from rocks and fossils.
Using rock and fossil evidence, the Silurian Period is further divided into 4 shorter portions of time. These smaller time divisions are called epochs.
The fossils in the Wenlock Limestone have helped to define an epoch known as the Wenlock. This name is used all over the world to describe rocks of the same age.
The Silurian Period was defined by Sir Roderick Murchison in the 1830's. He based the name on the Silures, a Celtic tribe living in the Welsh Borderlands at the time of the Romans.