Murchison 253 



had looked about for some appropriate and euphonious 

 term that would comprise his various formations and con- 

 nect them with that borderland of England and Wales 

 where they are so copiously displayed. This territory was 

 in Eoman times inhabited by the tribe of the Silures, and 

 so he chose the term Silurian a word that is now familiar 

 to the geologists of every country. 1 



At the same time Murchison published a diagrammatic 

 section of his classification which, except in one particular, 

 has been entirely sustained by subsequent investigation. 

 He there groups the whole series of formations as the 

 Silurian system, which he divides into Upper and Lower, 

 drawing the line of separation where it still remains. In 

 the upper section come the Ludlow and Wenlock rocks ; 

 in the lower the Caradoc and Llandeilo. The base of the 

 series, however, is made to rest unconformably on a series 

 of ancient slaty greywackes. No such base exists, for the 

 Llandeilo group passes downward into a vast series of older 

 sediments. At that time, however, both Murchison and 

 Sedgwick believed that a strongly marked separation lay 

 between the Silurian System and the rocks lying to the 

 west of it. 



Murchison used to maintain, with perfect justice, that 

 he had succeeded in his task, because he had followed 

 the method which had led William Smith to arrange so 

 admirably the Secondary formations of England. He was 

 able to show that, apart from mere lithological differences, 

 which might be of only local value, his formations were 

 definitely characterized, each by its peculiar assemblage of 

 organic remains. If Smith's labours had not only brought 



1 Phil. Mag. July 1835, p. 48. 



