868 Prof. Sedgwick on the May Hill Sandstone, 



Nor is this all. The sections of Caer Caradoc and Llandeilo 

 wei'e the assumed typical sections from which all the " Lower 

 Silurian '* nomenclature was derived. But the interpretation of 

 both these sections was (as has been already shown) erroneous ; 

 and I may securely state, that neither in the letter-press nor the 

 illustrations of the ' Silurian System ' is there one paragraph or 

 section which gives us a true notion of the geological place of 

 the groups of Caer Caradoc and Llandeilo. Again, I may state 

 that we have no right to mask a positive error by blotting 

 out our base, and by colouring all the older rocks of Cambria as 

 Lower Silurian. If the Lower Silurian groups were out of place, 

 no good nomenclature could be founded on them. Good nomen- 

 clature can only rest on phsenomena which are fixed and well- 

 defined. If all the rocks below the May Hill sandstone be 

 called Lower Silurian, no doubt the Caradoc and Llandeilo 

 rocks will remain Lower Silurian. But how do we gain this 

 supposed advantage ? By as strange an abuse of logic as is to 

 be found in the history of English geology ; by a supposed 

 development of two misinterpreted groups ; by making them 

 the typical representatives of the great Cambrian series ; by a 

 desertion of the principles from which all our good nomencla- 

 ture had previously been derived, and by throwing our true and 

 intelligible geographical names into an inextricable confusion. 

 Whatever scheme of nomenclature we adopt, let it be used con- 

 sistently. We cannot with impunity use two distinct schemes 

 of nomenclature, while we are professing to describe but one 

 geological system. 



Should any one object to my use of the word system as de- 

 scriptive of our great geological divisions, such as Primary and 

 Secondary, I should on that account have no quarrel with him, 

 for our difference would be one of taste, perhaps, rather than of 

 principle, and could lead to no misunderstanding. There is no 

 difficulty in finding consistent general terms for the great geo- 

 logical divisions ; and any one who prefers that use of the word 

 system, may in the foregoing Tabular View write system in the 

 place of series, and it will then give the whole succession under 

 the names Cambrian System, Silurian System, Devonian System, 

 &c. And I may conclude this comment on the Tabular View, 

 by stating (as I have done in a letter " On the Geology of the 

 Lake District *,") that I can still adopt, almost word for word, 

 the expressions published by myself twelve years since ; and can 

 affirm with truth that the two great divisions (Cambrian and 

 Silurian) differ in structure, interchange comparatively few fossil 

 species, and through large districts are unconformable. " Hence 

 they belong to two systems and not one, if the word system be 

 * Published by Hudson, Kendal (June 23, 1853). 



