184?7.] iMUKCHISON ON THE SILURIAN ROCKS OF N. WALES, ETC. 17S 



perhaps of all the Caradoe fossils ; whilst the associated Orthidse are 

 nearly all the very same simple-plaited species figured in my work, 

 and on which I have always dwelt as the best and surest types of the 

 Lower Silurian strata; viz. Orthis calligramma, O. vespertilio, O. 

 Jlabelluliim, O. Actonice, O. expansa, O. elegantula, O. Pecten, &c. 



Let these species be found m any part of the world, and I ask if 

 their discoverer can possibly assign to them any other geological name 

 than Lower Silurian fossils? 



And here I would say a few words on one of the propositions of 

 my friend Professor Sedgwick. Changing the old name " Lower 

 Silurian " into the new one of " Cambro-Silurian," and showing 

 that there is a considerable intermixture of Upper and Lower Silu- 

 rian forms in this group, he states with justice that it should never 

 have been cut off from the Cambrian. But why was it so cut 

 off? — simply, I repeat, because the zoological contents of the great 

 mass of the Cambrian rocks were unknown at the period when 

 the original classification was proposed. As soon as this point was 

 cleared up, I hold that the conduct I pursued, so far from being in 

 antagonism with the rules and analogies which have hitherto guided 

 geologists, was in direct obedience to the only canon on which their 

 nomenclature has been based — viz. conformity of succession and 

 similar organic remains. The only error committed was the origi- 

 nal one of giving a systematic name to a mass of rocks before its 

 fossils were known ; and I venture to declare it to have been not 

 merely my opinion, but that of every geologist who considered the 

 subject, that the continuance of the recognition of a Cambrian sy- 

 stem has been considered to be exclusively dependent on the disco- 

 very in it of a peculiar type of life distinct from that formerly de- 

 scribed as Silurian. 



In respect to the geographical propriety of language on which 

 my friend insists, I have already said that I was not responsible for 

 the outlines and contents of his Cambrian region ; and as to the 

 observation about the Silurian system being now brought by increase 

 of knowledge to mean nothing but " fossiliferous greywacke," 1 have 

 simply to remind him, that until the Silurian system was fixed, and 

 was followed by tracing the ascending succession of palaeozoic life 

 through the Devonian into the Carboniferous and Permian deposits, 

 foreign geologists had indiscriminately applied the word " grey- 

 wacke " to different members of this great palaeozoic series. But I 

 need not dwell on the advantages which followed from that first step 

 in the palaeozoic classification, as they have been kindly admitted by 

 my contemporaries, including Professor Sedgw-ick himself. 



Although it is unnecessary that I should deny, what I apprehend 

 no modern geologist can sustain, that peculiar lithological features or 

 extraordinary thickness can constitute any claim for the establish- 

 ment of a new nomenclature, I may be excused for requesting that re- 

 ference be now made to my former descriptions of such Lower Silu 

 rian strata when I found them intermingled with rocks of igneous 

 origin in the Silurian region. I then specially described districts in the 

 higher and western parts of Shropshire and in Radnorshire, in which 



