178 



DE. TVILLS AXD ME. SMITH OX THE LOWER [yoI. Ixxviii, 



III. Steatigeaphy. 



(A) General Considerations. 



The southern part of Denbighshire and the adjoining portion of 

 Merionethshire, described in this communication, form a rather 

 flat-topped upland, deeply dissected in the south-east bv the Dee, 



Fig. 1. — Outline-map showing the chief tectonic features of 

 the Llangollen district. 



INDEX 



Silurian 



Ordovician 



Carboniferous 

 ^ and Trias 



the Ceii'iog, and their tributaries. A depression runs north- 

 eastwards from Corwen across the upland, along the line of the 

 Brjneglwys Fault.^ The drainage from this flows in part to the 

 Dee and in part to the Alyn. In the northern part of the area 



^ Sometimes known as part of the Bala Fault, see p. 219. 



