64 SUPPLEMENT TO THE 



during so many years, his fossils undescribed, whilst Sir Roderick Murchison was having 

 his specimens described and illustrated by competent palaeontologists.^ 



Different schemes of classification have been proposed from time to time, but the 

 generality of geologists, both at home and abroad, have continued to maintain the 

 upper and lower divisions of the Silurian System, with some slight modifications ; and 

 this arrangement has been followed by the Geological Survey. 



I would refer the reader to Mr. R. Etheridge's valuable and important Anniversary 

 Address as President of the Geological Society, delivered on the 18th of February, 1881, 

 for an analysis and distribution of British Palaeozoic fossils, as shown in their geological 

 sequence. 



Mr. Etheridge has recently informed me that he adopts the following arrangement of 

 the Lower Palaeozoic rocks, commencing with the — 



1. Pre-Cambrian, comprising the Lewisian, Dimetian, Argovian, and Pebidian ; and 

 follows these in the ascending order by the 



2. Lower Cambrian : Longmynd, Harlech, and Llanberris. Few Brachiopoda. 



3. Upper Cambrian, comprising the Mencevian, Lower and Tipper Lingula- Flags, 

 Lower Tremadoc, and Upper Tremadoc. Brachiopods abundant in some of the sub- 

 divisions. 



4. Lower Silurian, comprising the Arenig rocks, Llandeilo, Caradoc-Bala, and 

 Lower Llandovery. In all these divisions Brachiopods are very abundant. 



5. Upper Silurian, comprising the TJpjier Llandovery or May -Hill Group, Wenlock 

 Series, and Ludloio Series, wherein Brachiopoda abound. 



While following the above arrangement, Mr. Etheridge gives the approximate number 

 of species that occur in each subdivision. I am also informed by that distinguished 

 palaeontologist that the Geological Survey would propose the following scheme for the 

 division of the Upper and Lower Silurian : 



Cambrian f Longmynd. 



C Harlech. 



^Lingula-flags ; lower, middle, and upper. 

 Tremadoc. 



A VPTll o* 



Lower Silurian of Survey <{ ^' 



Llandeilo. 



Caradoc. 

 .Llandovery. 



1 Twelve years after the publication of the ' Silurian System ' Prof. Sedgwick engaged Prof. M'Coy 

 to describe his fossils in a large volume, entitled ' A Systematic Description of British Palaeozoic Fossils in 

 the Geological Museum of the University of Cambridge,' 1855. This important work contains many 

 beautiful plates and full descriptions of new or little known species. Subsequently Prof. Sedgwick further 

 employed the late Mr. J. W. Salter to prepare ' A Catalogue of the Cambrian and Silurian Fossils con- 

 tained in the Geological Museum of the University of Cambridge.' This catalogue, completed by Prof. 

 Morris, was published in 18/3. 



