12 DENBIGHSHIRE SERIES OE SOUTH DENBIGHSHIRE. [Feb. 1895, 



To define the area a little more exactly, it extends from the 

 Holyhead road on the north to the Tarannon Shales on the sonth, 

 and from the ridge of Hoel-y-Gwynt on the west to the wooded 

 spur sometimes known as Wriddiog 1 on the east. In the western 

 part of the area a fault which runs a little north of east separates 

 this part of the basin from the more disturbed portion north of 

 the Dee. 



Throughout the greater part of this area the dip is between 

 north and east at a low angle ; but near the road it is frequently 

 horizontal or a little south of east, showing that we may place the 

 axis of the basin nearly along the line of the road. A little way 

 north of the Dee at Glyndyfrdwy the dip becomes southerly, and it 

 is also southerly in the southern part of AVriddiog. Farther north 

 we get into the disturbed region of the northern half of the basin. 



Physically, the area described may be considered as a somewhat 

 irregular plateau in which deep valleys of northerly direction have 

 been cut, leaving in the southern part a ridge stretching from east 

 to west, which forms the watershed between the Dee and the 

 Ceiriog. The culminating point of this ridge is Moel Ferna, at its 

 western extremity, the summit of which rises to a height of 2070 

 feet above the sea. From this two spurs project towards the Dee : 

 to the north is Moel-y-Gwynt, which runs towards Carrog and 

 overlooks on the west the flat and heather-covered valley of the 

 upper part of ISTant Llechog ; to the north-east a prominent spur 

 stretches as far as Glyndyfrdwy, but unfortunately bears few expo- 

 sures. Farther east the watershed throws out spurs which range 

 due north : a small one between the main and tributary branches 

 of Nant Arddau ; a second and larger one between Nant Arddau and 

 Nant-y-gro ; and a third, still larger, east of Nant-y-gro. This third 

 ridge, as it nears the Dee, bends round and runs towards the east, 

 forming the steep and striking slope on the southern side of the 

 Holyhead road about two miles east of Glyndyfrdwy. The wooded 

 spur Wriddiog is physiographically a continuation of this ridge, once 

 more bent round so as to run towards the north. 



IV. The General Sequence. 



At the northern end of the spur which runs north from Moel 

 Ferna the pale shales of the Tarannon series are succeeded by dark 

 banded slates, 2 which have been extensively worked at the Penarth 

 quarries of Pen-y-glog near Carrog. They have been already fre- 

 quently described, and contain Monograptus personatus, M. priodon, 

 Retiolites Geinitzianus, etc. 



1 This is unnamed in the ISfew Series of 1-inch Ordnance maps. It is the 

 spur which projects into the V-shaped bend in the Holyhead road shown on 

 the map. 



2 These slates are usually known in geological literature as the Pen-y-glog 

 Slates, from the name given to the hill on the old Ordnance maps. The name 

 ' Pen-y-glog ' is, however, almost unknown in the district ; and the quarries, 

 which are now no longer worked, were called the Penarth slate-quarries. 



