INTRODUCTION. Ixxxvil 
When Dr Fitton’s Review of the Silurian System appeared in 1841, the author of the System had not, I think, any 
perception of the fact that his lower groups were in a false relation to the Upper Cambrian rocks: and one or two years 
after the publication of the Review, when a controversy first arose between the author of the Silurian System and myself, 
he appealed to his original typical section—apparently at that time believing that his original order of superposition was 
true. His order was, Wenlock, Caradoc, Llandeilo, Cambrian; and as no general discordancy of position was known or 
acknowledged, the word Cambrian meant Upper Cambrian. The case of the Longmynd formed the only exception to 
this rule: for on the south-east side of that mountain-ridge there was an obviously discordant junction; and there the 
(exceptional) order was Wenlock, Caradoc, Longmynd rock. 
The order given in the Review is, at any rate, only a repetition of the order given in the typical sections and map of 
the Silurian System. Hence it is, I think, absolutely certain that when the author of the Silurian System described certain 
groups, thrown off from the older rocks of Pembrokeshire and from the north-western flank of the Longmynd, as Silurian, 
he believed them to be superior to the Upper Cambrian groups of Caernarvonshire, Radnorshire, and Merionethshire. 
There is no escape from this conclusion ; unless we concede to him the liberty of using such words as Llandeilo flag and 
Caradoc Sandstone, in one sense in the valley of the Towy, and in another in Pembrokeshire; in one sense in South Wales, 
in another in Shropshire—of using, in short, a palpable sophism. And if it appeared, in the progress of discovery, that 
some of the groups he had called Silurian were of a greater age than he had supposed, and that some others were the 
representatives of very old Cambrian strata; such a discovery would not prove that my Cambrian types were wrong; but 
would assuredly prove, that the author of the Silurian System had misunderstood some of his own sections, and given 
names to their groups which were inconsistent with the fundamental scheme of his own nomenclature. 
His first afterthought was to secure his nomenclature, and cover the mistakes of his typical sections, by absorbing 
Cambria into Siluria. This afterthought had however nothing to do with any mistake or inconsistency in the interpreta- 
tion of the sections thrown off from the north-western flank of the Longmynd—such, for example, as the Shelve, Stiper- 
stone, and Corndon Sections. To make them the prototype of Cambria was a much more recent afterthought: and to 
apply the term prototype to such sections was surely a very strange and imprudent abuse of language. 
When I began this note, I intended to examine critically the sections to which I haye last alluded. But I have 
abandoned this intention, in the fear that the note might become too long; and still more in the fear that I might, on some 
points of detail, misrepresent the author of the sections; for they are complicated and difficult, and I only know them 
at second-hand. Hence I have concluded in a general statement, which I think unquestionably true, and therefore unas- 
sailable. 
I may, however, just appeal to the sections of the Silurian System at Plate XXXI. fig. 4, and Plate XXXII. fig. 1. 
(1) About the Longmynd rocks there never was any doubt. (2) As to the rocks between the Longmynd and the Stiper- 
stones, they are also rocks of great antiquity; but they are no type of Cambria; nor were they given as such, or understood 
as such, by the author. (3) The application of the term Caradoc to the Stiperstones, and some beds above it, was probably 
a mistake. (4) The ascending sections are cut off unconformably by the overlying and discordant Silurian rocks. To call 
these sections types of Cambria is a strange imprudence; when it is virtually admitted that they become intelligible by help 
of other and truer Cambrian types; and to call them prototypes is a grave historical misstatement. The sections have 
however (especially when studied along with the map of “ Siluria”) another use:—they shew the absolute necessity of a true 
physical knowledge before any good classification can be attempted; for in no part of Wales is the great physical fact— 
that the true Silurian rocks are generally in a position discordant to the true Cambrian—more apparent than it is in the 
Longmynd sections. 
