The Ordovician Period extends in time from 505 million years ago until 438 million years ago. You will remember from our discussions of the Cambrian that the Ordovician Period of time and the Ordovician System ofrocks was suggested by Professor Lapworth as a means of solving the dilemma presented by Murchison and Sedgewick as to the "ownership" of a section of rock that both claimed when Murchison wanted to include the upper portion of Sedgewick's Cambrian System as the lower portion of his Silurian System. Sedgewick, you will remember, responded by demanding that the lower portion of his Silurina System be considered Upper Cambrian. Lapworth's solution was to place the disputed section ofrock into a separate system of rocks he called the Ordovician. Because there is no "type locality" for the Ordovician, there are those geologists who still refuse to recognize the Ordovician. However, the great majority of geologists worldwide do accept the Ordovician as a separate period of time and system of rocks.
Renton, John J. and Repine, Thomas, "The Ordovician Period" (2016). Readings and Notes. 17.