222. PROCEEDINGS OF THE GEOLOGICAL sociEeTy.  [Feb. 2, 
of the Silurian system, in the true original sense of that term. I 
have already shown their beautiful coordination to the true Silurian 
sequence, viz. Caradoc, Wenlock, Lower and Upper Ludlow, ending 
in Tilestone. 
7. But there may arise this question,—May not all the rocks, from 
the Skiddaw slate to the tilestone, be called the Silurian system? 
No doubt they may. But then arises another question,—Do all, or 
the greater part of the rocks below the Coniston limestone belong to 
the Silurian system, as the words were first used and as they now 
have currency? Are they the equivalents of any part of the Caradoc 
or Llandeilo series of that system? To such a question I can only 
give, as I have done before, a decided negative; and I believe that 
the assumed identification of beds in North Wales with the Caradoc 
and Llandeilo groups, because they contained certain fossils described 
in the Lower Silurian system, has led often to an entire misinterpreta- 
tion of the sections and the natural sequence presented by the physical 
groups. My objection to the extension of the term Silurian system 
to all the lower groups resolves itself into this proposition,—that no 
geographical name ought to be permanently accepted which does not 
refer us to a region contaiming a good typical series of the rocks so 
designated. Siluria does not contain a good series of the lowest 
fossil groups ; Cambria does. 
8. To this remark a reply has been made consisting of two state- 
ments: first, that the lower Cambrian or Cumbrian groups are with- 
out peculiar fossils. This is not quite correct ; and supposing it true 
that every species below the Caradoc group was also found m that 
group, the fact would only prove that the Caradoc group ought not 
to have been cut off from the Cambrian series, and that so far the 
Silurian system was without any zoological base-lme. In no sense 
can it be truly stated that the great Cambrian group is sterile of 
fossils, and must therefore pass without a name. If it have very 
remarkable physical characters and a great series of fossils, it must 
have some designation as a group. We cannot, while describing, in 
the order of nature, an ascending series of groups, wait for their desig- 
nation till we reach some higher and much more inconsiderable group, 
and then give back by reflection a name to the groups of anterior 
date, and already described. The second statement, in opposition to 
the previous views, is to the following effect: that the older fossil- 
bearmg groups in the Cambrian slates are only the development 
downwards of the lower parts of the Silurian system. I can compre- 
hend a progressive development from an older formation to a newer, 
and I believe that the Caradoc sandstone group might correctly be 
considered as the last development of a vast series of slate rocks, of 
which the true base is probably to be sought in Cumberland, among 
the central slates of Skiddaw. But a development downwards is 
something out of nature, when we speak of geological deposits, and 
involves a positive solecism both of language and meaning. The 
application of these remarks to the classification and nomenclature of 
the older rocks of Wales and Cumberland is too obvious to require 
any further comment. 
Te. )- = s S 
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