156 Sir Roderick I. Murebison on the 



Cambrian rocks were unknown at the period when the original classi- 

 fication 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 nomencla- 

 ture has been based, — viz., conformity of succession, and similar or- 

 ganic remains. The only error committed, was the original 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 system has been 

 considered to be exclusively dependent on the discovery in it of a 

 peculiar type of Z^yb, distinct from that formerly described as Silu- 

 rian. 



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 observa- 

 tion about the Silurian system being now brought by increase of 

 knowledge to mean nothing but " fossiliferous greywacke," I 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 " greywacke" 

 to different members of this great pala30zoic series. But I need not 

 dwell on the advantages which followed from that first step in the 

 palceozoic classification, as they have been kindly admitted by my 

 contemporaries, including Professor Sedgwick himself. 



Althougli it is unnecessary that I should deny, Avhat 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 

 reference be now made to my former descriptions of such Lower Si- 

 lurian 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 contemporaneous submarine volcanic rocks alternated frequent- 

 ly with beds containing Lower Silurian fossils ; such masses having 

 been subsequently penetrated by other eruptive matter. Those con- 

 temporaneous trap-rocks were stated to be made up of many varieties, 

 including felspatliic grits, sandstones, conglomerates, and breccias, 

 greenstone and horneblendic rocks of many shades, with porphyries, 

 &c. Now, although these rocks had a very diff'erent mineral aspect 

 from that with which I was familiar in districts removed from such 

 disturbing causes, I never thought of applying a separate name to 

 them. They had, it is true, a peculiar aspect. They were often 

 much swelled out by the interlacement of porphyries, greenstones, 

 and " volcanic grit," and owing to these conditions, fossils were com- 



