﻿Vol. 64.] BALA AND LLANDOVERY EOCKS OF GLTN CEIEIOG. 551 



Ferna, but towards the east it is clear that he was deceived by 

 the fault that runs from Dol-y-Wern towards the south-south- 

 east. 



Since the appearance of Davies's paper but little has been 

 written on the area in question. Mr. Thomas Euddy gave a list of 

 fossils from Cef n-goed, Nant lorwerth, and Pont Hafod-y-gynfawr ; 

 Prof. Hughes has published a list of fossils from the supposed 

 Corwen Grit of the latter locality, and we ourselves have added 

 several species to this list. Mr. T. H. Waller has described a 

 specimen from the ' China-ash bed' near Pont-y-Meibion, and con- 

 cludes that it is a volcanic ash. This is the lowest ash of the 

 Geological Survey. 



The last paper to which it will be neccessary to refer was com- 

 municated by Messrs. Cope & Lomas to the British Association in 

 1903. In it they maintain that the ' greenstone ' of Hendre, south 

 of Pandy, and the three ash-bands shown on the Geological- Survey 

 map are all intrusive. "With regard to the greenstone there has 

 never been any question, and there is little doubt that the Coed-y- 

 glyn rock, which Messrs. Cope & Lomas identify as the 'Little Ash' 

 of Jukes, is also intrusive. But in the case of the other bands we 

 find no evidence of intrusion, and we agree with the majority of 

 previous observers that they consist chiefly of ashes and tuffs. As 

 will be shown in the sequel, the rock of the Coed-y-glyn quarries 

 is not the ' Little Ash ' of Jukes. 



III. Section in the Glyn Valley. 



Despite the long strike-fault mentioned in the introduction, by 

 far the most perfect section in the district is exposed in the valley 

 of the Ceiriog between Glyn and Pandy ; and, in order to make the 

 general succession clear, it will be convenient to begin with a brief 

 description of this section, supplementing it by a short account 

 of the upper beds, which are not shown in the valley itself, but 

 appear on the hiUside in the immediate neighbourhood. We shall 

 then take each of the subdivisions in turn and describe it in detail, 

 tracing its distribution throughout the area of our map. 



Cwm-Clwyd Ash. — So far as we have seen, the dark slates and 

 sandstones that lie below the lowest band of ash are, in this neigh- 

 bourhood, almost completely unfossiliferous ; and, as they hardly 

 come within the area with which we are concerned, we shall leave 

 them out of consideration, and begin with the lowest ash-band 

 itself, which may be termed the ' Cwm-Clwyd Ash.' 



This is formed of some 250 feet of volcanic rocks, which are very 

 distinctly bedded and include ashes and tuffs of various degrees of 

 coarseness. The whole series is finely exposed in the cliffs at the 

 entrance to the lateral valley known as Cwm Clwyd. 



Teirw Beds. — The ash is succeeded by a band of slate, fol- 

 lowed by a great mass of sandstones with intercalated beds of 



