POSTSCRIPT TO THE INTRODUCTION. XxeV 
their arrangement, are substantially my own. They were made out with no small labour; 
and nearly all of them were first named as distinct physical groups by myself. Let then 
the lowest six groups—(1, the Longmynd strata; 2, the Llanberis slates; 3, the Harlech 
grits; 4, the Lingula flags; 5, the Tremadoc beds; 6, the Arenig porphyry and Festiniog 
slates ;)—stand as they are arranged in Professor Phillips’ vertical section, and be called 
Cambrian. 
Afterwards (in the Manual) follow in regular ascending order :—7, Lower Bala, slates, 
flags, &c.; 8, Bala limestone; 9, Upper Bala, slates, flags, &c.; 10, Caradoc sandstone 
These four groups are called Lower Silurian. Here there is a divergence in our 
nomenclature. I call them Cambrian, in the Tabular view. 
Continuing the ascending section, and commencing with the May Hill Sandstone, we 
have seven ascending groups, (No. 11—No. 18,) about which (excepting No. 11) there 
never has been a dispute. They are the rightful conquest of Murchison—the Silurian 
Series of the Tabular view—the Upper Silurian rocks in the Manual of Phillips. 
To justify this scheme of classification and nomenclature, (Manual, p. 105), there 
surely ought to be some great change (physical or paleontological, or both together) before 
we alter the names of the collective groups from Cambrian to Silurian. But there is no 
such change or break of continuity. There is nothing to indicate such a break in the 
sections north of Tremadoc, in the grand sections on the Holyhead road, or in the sections 
near Festiniog. If the Tremadoe slates and the Festiniog slates be Cambrian, the Bala 
group is also Cambrian. Hence, spite of its historical injustice, its geographical incongruity, 
and its abandonment of first principles, I think that the scheme adopted by Murchison in 
1843, and still vindicated in 1854, is more logically consistent than the scheme proposed 
by Professor Phillips in 1855. The scheme of Murchison, below the May Hill Sandstone, 
is consistently wrong. The scheme of Phillips is partly right and partly wrong. 
Let no one suppose that I am in this remark flinching from my own scheme of 
nomenclature. I am doing no such thing. JI am only pointing out what I think the 
inconsistency of calling the collective Bala group Silurian, while the lower groups are 
called Cambrian. What we at present most want is a better analysis of the great Bala 
group, and especially of its upper sub-groups in South Wales; and I believe that the 
unfortunate and illogical adoption of the Llandeilo Flag as the guiding type of this great 
collective group, and the erroneous incorporation of it into the system of Siluria, by the 
Government Surveyors, have stood in the way of its more perfect analysis. They seem to 
have been cramped by a confined and utterly inadequate nomenclature. Their true work 
was to make out the older physical groups of South Wales, and separately to name them ; 
and then to give them some good collective name: and I do not think they could have 
found a better collective geographical name for them than Upper Cambrian, which I had 
used long before they made their first essay upon the older Paleozoic rocks of Britain. 
Again, if the scheme given in the Manual (p. 105) were logically consistent, there 
surely ought to be a far more decided break between the Festiniog slates and the Lower 
Bala slates, than there is between the Caradoc and the May Hill Sandstone. But such 
