Ixxviil INTRODUCTION. 
great mistake, directly bearing on nomenclature, had been committed by the author of the 
“System” (the greatest mistake in the history of British Paleozoic geology); while in the 
interpretation of my own sections, and in the true and consistent geographical nomenclature 
I derived from them, I was not convicted by the Government Surveyors of one single mistake 
of principle affecting the natural classification of the groups. 
Let us now examine the second sentence of the previous extract. The author described 
the rocks on the western flank of the Longmynd with many excellent details. About the 
Longmynd rocks there was no dispute. They were certainly very ancient rocks, and when 
asked (in 1834) my opinion of their age, I told my friend that I should provisionally identify 
them with a portion of the Skiddaw slate of Cumberland. Above the Longmynd rocks 
were other very difficult and obscure rocks, some of which were also very well described in the 
“Silurian System.” Then came the Llandeilo Flag; after which the ascending section was 
broken and defective. Part of this series was called Silurian; but the section was not typical, 
nor was it appealed to as the basis of the nomenclature. Its groups were named from other 
sections that were then regarded as typical, and were the basis of the nomenclature: and it 
is as certain as any fact can be in the history of geology, that the so-called Silurian rocks 
of the above section were supposed (at the time of the publication of the System and for 
some years afterwards) to be superior to the Upper Cambrian group. If then, in the progress 
of discovery, it turned out that some of the rocks of this section, which the author had named 
Silurian, were rocks of a much greater antiquity than he had first supposed, this did not make 
them typical; nor did it (as he wishes to prove) convict me of error. But it did prove, out of 
all question, that he had misinterpreted, and therefore had misnamed, some of the rocks of his 
section on the western flank of the Longmynd. To desert his original Silurian types, while 
he retains their names—then to give a new meaning to such names, by shifting his ground 
and appealing to a new type where these names had been applied by a positive blunder of 
interpretation—then on such grounds to contend that he has now both physical and fossil 
evidence to offer in vindication of his System—and lastly, to contend that in placing my 
Lower Cambrian groups many thousand feet below his “well-known Lower Silurian rocks,” 
I had made a blunder, while he had all the while been interpreting the sections correctly ;— 
al this is, I affirm, neither true history, nor good advocacy. It appears to me nothing 
but a mystification of the whole question, by a plain shifting of the meaning of plain 
words, while we are working our way to a foregone conclusion—a kind of sophism by 
which men unconsciously impose upon themselves as well as upon others. 
One more quotation, and I have done with my remarks on the second chapter of “ Siluria.” 
‘Miniature as it is in comparison of North Wales, this tract of the Stiperstones and Shelve, 
which with a description of its fossils was formerly described and mapped as Lower Silurian, 
and which extends from Shropshire into Montgomeryshire, is, I repeat, now determined to be 
the geological prototype of the grander undulations of the same rocks which spread over so 
large a portion of the Principality of Wales.” (p. 39). Ifthe author had entertained even the 
remotest suspicion that the tract here described contained the representatives of the whole 
