iv ADVERTISEMENT TO SECOND FASCICULUS. 
The series of old slate-rocks, found in the Longmynd, and the neighbouring parts of 
Shropshire, are not included in this Tabular View; because no fossils have been discovered 
in them, and because their exact place in the general series is doubtful. They are, probably, 
in part co-ordinate with, and in part inferior to, the Llanberis slates. I believe them also to be 
physically co-ordinate with the Skiddaw slate—the lowest Cumberland group. 
In the Advertisement prefixed to the first Fasciculus (May 1851), IL have stated “that the 
Caradoc group has, perhaps, no distinct representative in Scotland and the North of England.” 
Since the Advertisement was written, I have revisited some parts of the North of England, and 
now think (for reasons published in the Journal of the Geological Society, Vol. vit. Part 2) 
that the Coniston grits are the true representatives of the Caradoc group. 
In the same Advertisement I divided the Cambrian series into two groups—Upper and 
Lower :—the upper commencing with the Bala limestone. In the previous Tabular View I 
have not made any use of the terms Upper and Lower Cambrian ; but I have divided the whole 
series into what I think good natural groups derived from actual sections. Were I now to 
make use of the term Upper Cambrian, it would include all the strata under Nos. 3 and 4 of 
the Tabular View: and in this arrangement the upper Cambrian groups would commence 
(several thousand feet below the Bala limestone) with the black slates at the East of Great 
Arenig, and at the South-East side of Cader Idris. In my present scheme of nomenclature the 
Bala group is the equivalent of all the undulating rocks of South Wales which are inferior to 
the true over-lying Silurian groups, and are superior to some older groups (Festiniog groups) 
which emerge in a part of Pembrokeshire. 
The old subdivision of the Cambrian series into upper and lower—(the upper com- 
mencing with the Bala limestone)—though I now think inconvenient for Wales, would not be 
inconvenient for the groups of Cumberland and Westmoreland. The Paleozoic system, in the 
North of England, may be arranged naturally in the following sub-divisions :— 
Carboniferous. 
Old red sandstone. 
Silurian= All the Lower Paleozoic rocks above the Coniston grits. 
e Coniston grit = Caradoc sandstone. 
Upper ...{ 6 Coniston flags = Upper Bala. 
a Coniston limestone = Bala limestone. 
Cambrian. . . 
Lower Bala and Fes- 
pete | Great zone of Green slate and Porphyry = { Eavaca scare, 
Skiddaw slate = Bangor and Longmynd group ? 
I do not, however, give this scheme in opposition to the preceding Tabular View, as I think 
that the nomenclature of the older British paleeozoic rocks can only be fixed by a reference to 
the more perfect Silurian and Welsh sections. 
At p. 332, and ending p. 350, is given a List of all the Lower Paleozoic Fossils described 
in the work, with a reference, in each case, to the page where any species is described. The 
genera are given systematically, and in the order in which they appear in the body of the work. 
