184'6.] SEDGWICK ON THE FOSSIL SLATES OF N. WALES, ETC. 163 



stand in the exact place of our " old fossiliferous greywacke ; " i. e. 

 every fossil-bearing rock, of whatever age, below the Old red sand- 

 stone. 



Thus are we led to confound what before we had separated ; and 

 the new classification is a retrograde movement, and not an advance, 

 in the progress of a good nomenclature. And all this is done with 

 the additional incongruity, that a geographical term is to be retained 

 without a geographical meaning; and under the Lower Silurian groups 

 we are to comprehend great groups of rocks not found in Siluria. 

 Nor is this all : we are on this new scheme of nomenclature to ex- 

 punge the term Cambrian, as applied to the older division of our 

 slate rocks, though the Cambrian region does contain (and is the 

 only British country that does contain) all the fossiliferous groups of 

 this division. These remarks appear to me at once decisive as to 

 the question in debate, and to settle the natural grouping of our 

 older rocks on a firm basis, provided we retain a geographical no- 

 menclature. 



Can the lower division of the Silurian groups {i. e. Caradoc and 

 Llandeilo groups) be considered, on any fair interpretation, as the 

 representatives or equivalents of the lower fossiliferous groups of 

 Wales ? If so, the name " Silurian System " might be correctly given 

 (though still I think not conveniently) to the whole series of Cam- 

 brian rocks. Sir R. I. Murchison seems to have decided this ques- 

 tion in the affirmative (misled perhaps by some memoirs read before 

 this Society since the publication of his ' System '), when he ex- 

 punged his whole base-line and removed it to the western coast of 

 Wales — incorporating in the Silurian system all the older Cambrian 

 groups. I know that this was the interpretation first put on the phae- 

 nomena ; but I now contend that the new nomenclature was not 

 merely an innovation, but an innovation founded on a mistake as to 

 the structure and development of the formations in North and 

 South Wales. At the time the innovation was introduced, I entered 

 no protest against the new nomenclature ; but I never adopted it. 

 Wishing only to be guided by facts, I gave it a fair trial ; and 

 during 184^2 and 1843 I again went over some of the North Welsh 

 sections, and honestly endeavoured so to interpret them that their 

 higher groups might be considered as a great expansion of the Cara- 

 doc sandstone, and their lower groups as the representatives of the 

 Llandeilo flag ; for at that time I supposed (what I now know to be 

 a mistake) that the Llandeilo flag was a distinct group below the 

 Caradoc sandstone. This attempt was however in vain ; and at the 

 end of the summer of 1843 I found, as stated in a former paper*, 

 that the only beds in North Wales I could bring into any close com- 

 parison with the Llandeilo flags were at the top of the whole Cam- 

 brian series, and not (as they ought to have been, in conformity 

 with the new nomenclature) at the bottom. This conclusion has 

 been fully confirmed by what I have seen during the past summer ; 



* Geol. Journ., vol. i, p. 5. 



