﻿554 DE. T. GE003I AXD MR. P. LAKE OX THE [NoV. I908. 



Ceiriog fossils are very abundant in some places. The fossils are 

 distinctly Llandovery forms, and differ considerably from those of 

 the beds below. 



Ty-draw Slates. — On both sides of the Ceiriog the Fron-Prys 

 Slates are succeeded by a considerable thickness of pale greenish 

 slates, resembling the Tarannon Shales of other areas. They are 

 visible at many points, and have been extensively quarried on the 

 northern slope of Mynydd Fron Frys. 



Denbighshire Slates. — The green slates are followed, ap- 

 parently with perfect conformity, by the dark slates that form the 

 lower portion of the AYenlock Series in this district. The relations 

 of the two are not very well shown in the valley itself; but at 

 Cefn-isaf the green slates are interbedded in their upper part with 

 black bands very similar in character to the Denbighshire Slates, 

 and the boundary appears to be very vague and indistinct. The 

 Denbighshire Slates themselves are well exposed in the Glyn 

 quarries and also elsewhere in this neighbourhood, but we do not 

 propose to deal with them at length in this communication. 



This completes the succession, so far as it is exposed in the 

 valley of the Ceiriog between Pandy and Glyn Ceiriog, and ex- 

 cepting at the Dolhir Fault the sequence is apparently unbroken. 

 This fault, however, cuts out the base of the Dolhir Beds and the 

 top of the Bryn Series, and in the valley itself it is by no means 

 clear how much of the succession may be missing. Fortunately, the 

 fault runs somewhat obliquely to the strike, and consequently higher 

 beds of the Bryn Series are exposed towards the east, while the beds 

 below the Dolhir Series are exposed towards the west. The latter 

 are dark graptolitic slates, entirely distinct from both the Bryn and 

 the Dolhir Series ; we therefore group them separately, and the 

 whole succession, so far as it is exposed in the area of our map, 

 is as follows : — 



Denbighshire Slates. . = Wexlock. 



Ty-draw Slates "[Taraxnon & 



Fron-Frys Slates J Llaxdoveey. 



Glyn -Valley f Glvn Grit and Limestone 



Series. [Dolhir Beds 



Graptolitic Slates 



Break. 



f Pen-y-2;raig Ash 



p., 



Bi'jn Beds 

 Pandy Series. < Craig-y-Pandy Ash 



Teirw Beds 



(Cwm-Clwyd Ash.... 



