part 2] LOWER paleozoic or the llangollen district. 217 



the map (PL V) brings out this rippling structure which, as it 

 approaches the Dee Valley, becomes very much complicated by 

 faulting (fig. 4), as was shown many years ago by Dr. Groom & 

 Mr. Lake.i Of the faults, the east-and-west faults are now seen to 

 be parallel to the Llangollen Fault and probably part of it, while 

 the others may be grouped with the north-west or north-and-south 

 adjustment-faults. 2 



The buttress doubtless operated to some extent as a resistant 

 mass, comparable in its effects to the Cricor and Cyrn-y-Brain 

 domes, and like them it has been truncated by the master-faults 

 where it merges into the adjoining synclinal structures. 



Berwyn Nodal Anticline. — The northern fringe only of 

 the Berwyn Anticline falls within the scope of this paper. The 

 region to be described may be said to be introduced by the Glyn- 

 Ceiiiog Fault to which reference has already been made (p. 213). 

 The fault throws down northwards, and may also represent a west- 

 ward movement on its north side ; but its exact position and 

 amount of displacement is not determinable with certainty. In 

 the Moel-Fferna region it can be fixed fairly closely by reference 

 to the easily recognizable grits and pale slates ; but it is rather 

 inferred than proved between the Moel-Fferna Slate-Mine and 

 Glyn-Ceiriog, although from place to place signs of faulting have 

 been noted. In the Glyn district it may have been touched in 

 the Wjmne Slate- Quarries, and its course down the valley to 

 Llwjai-mawr is obviously implied by the abrupt termination of the 

 Pen-y-glog Slates, the Yalentian, and the Glyn Grit, on the south 

 side, and the introduction of the Glyn-Dyfrdwy stage on the north 

 side of the valley. This was not appreciated by Dr. Groom and 

 Mr. Lake, and appears to nullify some of their arguments for the 

 movements postulated for the Cae-mor Fault.^ 



Near Dol-y-wern the Glyn-Ceiriog Fault probably divides into 

 three branches, the westernmost of which is the Cae-mor Fault 

 of Groom & Lake. It is not certain by any means which • of 

 the three lines forms the true continuation of the Glyn-Ceiriog 

 Fault towards the south-east. If it be the Cae-mor, there is an 

 abrupt change in strike of the fault ; and it is more likely that the 

 middle branch which runs into the greatly disturbed region west of 

 Craignant was in pre -Carboniferous times the most important 

 structural fault. On the other hand, the northernmost branch 

 swings round into a fault-line of great importance in post-Carboni- 

 ferous times, which passes across the coalfield at Chirk. The 

 ground east and south-east of Dol-y-wern is complex, and ob- 

 scured by Glacial drift. No attempt at finality can be claimed 

 in the solution of the faulting hereabouts, and therefore we do not 



1 Q. J. G. S. vol. xlix (1893) pp. 426-39. 



^ The part of the map (fig. 4) neighbouring' Corwen incorporates that of 

 Groom & Lake with modifications in mapping by the present authors. 

 3 Q. J. G. S. vol. Ixiv (1908) pp. 585-87. They spell it ' Cae-mawr.' 



