XXViil INTRODUCTION. 
of the Rhenish provinces) seem to run into an intimate union with the Silurian. Hence it 
appears to me by no means improbable that we may be hereafter induced (provided we 
continue to separate the whole Palzeozoic System, as in the Tabular View, into three primary 
Divisions) to place the Silurian Series not in the Lower, but along with the Devonian Series 
in the Middle Division of Paleozoic rocks. I only throw this out as a mere hypothesis; and 
if it be hereafter adopted, it must be on a wider base of evidence than is at present supplied 
by the Palzeozoic System of England. 
Thirdly. Though the Devonian Series, of the Herefordshire type, seems to pass down- 
wards into the Upper Silurian groups, it does not appear to pass upwards into the Carbon- 
iferous. There is generally a paleontological and physical gap between them, which is in 
many places obscurely indicated by the Upper Conglomerates of the Old Red sandstone. - 
Now this gap is, if I mistake not, filled up by by the higher Devonian groups in Cornwall 
and Devonshire. In those counties, when we draw a line between the Devonian and Car- 
boniferous rocks, we find the physical and paleontological evidence in positive conflict. For if 
we go on the single principle of counting species, the Petherwin and Barnstaple groups (as was, 
I believe, first pointed out by Mr Griffith on the specific determinations of Professor M°Coy) 
must be packed with the Carboniferous Series. But in so doing we deprive of all importance 
a grand group of dark slates and flags, which seem to have been laid down by nature’s hand 
as the true and continuous base of the great Culm-trough of Devonshire and Cornwall. Nor 
is this all. The Petherwin and Barnstaple groups, along with many true Carboniferous types, 
contain several genera and species which have not hitherto been considered as Carbon- 
iferous. In such a case as this we may strike a balance in the conflicting weight of evidence 
offered by the groups, by giving them an undefined margin, and by adopting a provisional 
nomenclature *. 
Fourthly. There is in like manner, in some localities, a great difficulty in drawing the 
demarcation between the Carboniferous and Permian Series. This difficulty was acknow- 
ledged by Smith in his old Geological Map of Yorkshire, in which he classed the * Lower 
Red Sandstone” (or Permian Sandstone of a more modern nomenclature) as one of the coal- 
measures. The difficulty was also fairly stated by myself in a paper (founded on independent 
observations made in 1821, 1822, and 1823) published in the “ Transactions of the Geological 
* The case of the Old Red sandstone of the North of England has not been prominently noticed. It generally 
appears (as above stated) in the form of a very coarse conglomerate, which, if I mistake not, represents only the wpper part 
of the Devonian series. In following the base of the Carboniferous rocks (as they wind round the Cumbrian mountains) 
we in several places find them underlaid by a coarse red conglomerate, and in a few places both by red conglomerate and 
red sandstone. In the latter case (e.g. in the neighbourhood of Shap Wells) the beds of red sandstone are perfectly 
parallel to the overlying beds of the Great Scar-limestone. Nor is this all. Beds of red sandstone, of an identical mineral 
type, alternate, in thick masses, with the beds of the Great Scar-limestone; as may be seen in several places in the fine 
sections between Ravenstone Dale and Shap, and thence into Cumberland. In all such cases there is obviously an intimate 
union between the Old Red and the Carboniferous series—a fact which seems to sanction the opinion that the Old Red 
conglomerates of the North of England represent only the upper part of the Devonian series. 
+ A work not without some errors, but of very great merit considering the early date of its publication (1821). 
