The Silurian System

Trilobite Plate

The Silurian Period of geological history is defined between 444 million years ago and 416 million years ago. It is named after an ancient welsh tribe from the Roman times, called the Siluries. The scientist credited as defining the Silurian period was a short Scotsman named Sir Roderick Impey Murchison in 1835.

Work began in 1831 by visiting many successions of the midlands and welsh borderlands which took until 1833 to classify all of the rock formations. Rock samples brought back by Charles Darwin and other geologists helped to reveal the worldwide distribution of Silurian rocks by studying the fossils and comparing them to British examples.

The evidence used to define the period was collaborated into his book entitled “The Silurian System”, of which 65% of the fossils used were from the Wrens Nest, Dudley. The source of the huge range of Dudley fossils was the Much Wenlock Limestone Formation (formally known as the Dudley Limestone) deposited in a shallow, tropical lagoon about 20 degrees south of the equator, around 425 million years ago. He compiled fieldwork from around the UK including the welsh borders. Sir Roderick’s work was subscribed to by many other geologists of the day such as, the Rev. Buckland who described the Megalosaurus and Prof. Adam Sedgwick, founder of the Devonian and Cambrian systems.

Wrens Nest in 1839

The 1st edition was originally published in 1839, and sold out almost immediatly. Dudley Museum and Art Gallery still has an original 2nd edition of the book on display in their “Dudley Un-Earthed” exhibition. The book contains a catalogue of many Silurian fossils including original specimens held by Dudley Museum.

The pioneering book was not without controversy, as Adam Sedgwick, Professor of Geology at the University of Cambridge argued that it included older rocks, part of the Cambrian System. This feud was eventually settled by Professor Charles Lapworth from the University of Birmingham. Lapworth used his understanding about lower Palaeozoic faunas to separate Sedgwick’s Cambrian System and Murchison’s Silurian System with the Ordovician System.  Although, the Ordovician System was not widely accepted until 1960 as it was previously referred to the Gotlandian after a Swedish island.

Murchison's original Eucalyptocrinus crinoid specimen

The Eucalyptocrinus specimen as drawn by Lady Murchison

Far left is the original specimen collected by Roderick Murchison next to the drawing by Lady Murchison in the book ‘The Silurian System’.

This can be seen on display in Dudley Museum and Art Gallery.

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