698 THE SILURIAN ROCKS OF THE VALLEY OF THE CLWYD. 
called Dinas, gets on to the Denbigh Flags less than a mile W.S.W. 
of Derwen Station (see fig. 2). 
The succession is better seen here than in the Bod Renail section. 
To describe the beds, as in the case of fig. 1, in descending order, at 
Derwen Station we have the Denbigh Flags, the equivalent of m in 
fig. 1. These can be followed along the hill-side and river-bed by 
Meiarth, dipping on an average about 20° to 30° E.S.E. 
About + mile W. of Meiarth gritty sandstones similar to those on 
Garwfynydd crop out. They are thrown down to the level of the 
stream by a small fault along which a trial has been made for lead. 
In the flags immediately W. of the fault [found Mongraptus vomerinus. 
These flags have several subordinate beds of sandstone, especially in 
the lower part where they pass into the pale slates. 
The pale slates are well seen in the banks of the Clwyd near 
Glynbach, and in the little stream-course running down from Clegyr- 
mawr, a considerable way below the position assigned to them on the 
Survey map. They consist of alternations of light-grey wavy banded 
sandstones and pale pasty and sandy mudstones with darker bands. 
In the lower part there are black bands from 2" to 6” thick con- 
taining a group of Graptolites, which, with the exception of Mono- 
graptus colonus, are common forms in the Graptolithic mudstones of 
the Lake-district. 
The Graptolites I found were :— 
Monograptus convolutus, His. Monograptus tenuis, Portt. 
triangularis, Harkn. colonus, Barr. 
The Corwen Grit comes out from below the pale slates and 
occupies all the high ground to the W. A small fault crosses the 
Clegyrmawr stream obliquely, and has been followed for lead, which 
seems to oceur principally, if not exclusively, where the sandstones 
arefaulted together. The workings do not appear to have pierced beds 
older than the Corwen Grits; and in the waste rock carried out of 
the level I found an obscure head of an J/lenus. 
On the whole, therefore, it seems clear that we have here a base- 
ment series for the Silurian corresponding in all its details to the 
base of the Silurian made out in Yorkshire and Westmoreland ; and 
that here also, as near Corwen, some of what has been included in the 
Bala must now be referred to the May-Hill Sandstone and higher 
beds. 
