XIV INTRODUCTION. 
work are due, exclusively, to Professor M’'Coy; and during the first two years of his systematic 
work on the older Paleozoic fossils, he had, from myself, no clue toward an exact determi- 
nation of the geological groups of strata to which the several species were subordinate. 
Each species was determined on its own evidence, without any warp or prejudice; and I had 
learnt by past experience that this was a matter of some moment*. But when the Second 
Fasciculus was well advanced, I gave my friend that more exact and detailed classification 
of the older Palsozoic rocks which was afterwards prefixed to it as a “Tabular View.” 
(Advertisement to the Second Fasciculus, p. iii.) He then proceeded to group the species 
geologically in agreement with this scheme; and, in conclusion, he drew up (checked and 
assisted by myself on points that were local or geographical) the three lists which commence 
at p. 326 and end at p. 374 of this volume: viz. Alphabetic and Systematic Lists of all the 
Lower Palzeozoic Fossils, and an Alphabetical List of all the Localities. 
When this work was done there was no difficulty in confronting physical and fossil 
evidence, so far as the subject could be illustrated by the Cambridge collection; and in 
seeing how far the development of organic species accorded with the succession of those 
natural groups of rocks, which were indicated by my sections, and enumerated in the Tabular 
View. With one exception, the accordance was as good as we had any right to anticipate. 
This exception was found in the so-called Caradoc group; which in the sections and 
lists of the “Silurian System,” and in the Government Survey, was regarded and described 
as a group wherein the most characteristic Cambrian and Silurian types were so blended 
as to be inseparable, either on zoological or physical evidence. This I had admitted on 
such high authority, though the conclusion bore against myself; and it had never been 
my task to examine, critically and in detail, any one of the most typical of the so-called 
Lower Silurian sectionst. While under this belief, I had for several years supposed that 
there was an overlap between the Upper Cambrian and the Lower Silurian groups; and I 
had once proposed, for a part of my Upper Cambrian group, the name Cambro-Silurian, 
as an intermediate term which would include all doubtful cases, give every labourer his due, 
and secure a congruous and correct geographical nomenclature. 
1844 he made, at my request, a short tour with a view of ascertaining the relations of the undulating groups of the Rad- 
norshire mountains to the Llandeilo group of Builth, but did not arrive at a satisfactory result. At that time I was secking 
health at a German bath and not able to take the field with him. 
* T here especially refer to the fact, that in 1836 a set of Barnstaple fossils (collected by Sir R. I. Murchison and 
myself from beds which at first sight we supposed to be Caradoc sandstone) were sent to London for examination; and 
the species were, after examination, returned as “Caradoc.” Taking this as a point established, I endeavoured, in 
yain, during portions of the two following summers, to torture the Cornish and Devonian sections and fossils into an 
agreement with it. But when the truth of the Devonian sections became, at length, firmly settled, the Barnstaple fossils 
were re-examined, and proved to be all either of Devonian or Carboniferous species. How entirely Professor M°Coy was 
unacquainted with the fossil localities of North Wales, during the progress of his work in Cambridge, is obvious from 
the mistakes he has made, in reference to the place of certain fossil groups, in some of his early papers in the “ Annals and 
Magazine of Natural History.” Thus, under the name Wenlock shale, he has united the shales of Builth Bridge with the 
Llandeilo shales which are north of Builth. The same errors are, I find, repeated in a reprint (by Macmillan and Co. of 
Cambridge) of these yery valuable papers, under the title of “Contributions to British Palzontology ;” but they will be 
corrected in a list of errata. 
‘+ See the Advertisement to the First Fasciculus, and compare it with the Advertisement to the Second. 
