18 



MR. PHILIP LAKE ON THE DENBIGHSHIRE [Feb. 1895, 



Moel Ferna Slates. 



It is only on Moel Ferna itself, where they have been quarried, 

 that these slates can be recognized as distinct from the overlying 

 flags. In character they are precisely similar to those of the 

 Penarth quarry ; but fossils are very rare. It was only in one or 

 two blocks in the waste-heaps that I was able to obtain Mono- 

 cjraptus priodon, Bronn, and M. Flemingi, Salter. 



Judging from the character of the rock and the rarity of fossils, 

 it seems possible that the slates of Moel-y-Faen, 4 miles north of 

 Llangollen, lie on the same horizon as these. 



Nantglyn Flags. 



The succeeding series, to which we may appropriately apply the 

 term already employed by Prof. Hughes in the Vale of Clwyd, con- 

 sists of a great thickness of flaggy beds, which are mainly dark in 

 colour, but are streaked with numerous very fine, lighter-coloured, 

 and more gritty bands. Usually they split in the direction of the 

 bedding and form the flags from which the whole series takes its 

 name ; but when the cleavage is better developed they break up 

 into rhomboidal fragments in which the streaked appearance is 

 well seen. 



At the Deeside slab-quarries, south of Nant Arddau, they have 

 been worked on a large scale, and the following fossils occur : — 



OrtJwceras primesvum, Forbes. 

 „ ISedgwicJci, Forbes. 



„ ventricosum, Sharpe. 



Carddola. 



'Actinocrinus' pulcher, M'Ooy. 



Mo?wgrajptus colonus. 



The specimens of Actinocrinus pulcher are sometimes extremely 

 fine. Large slabs are covered with complete casts of the whole 

 animal, with all the minutest branchlets beautifully preserved. 



These flags extend across the valley to the east, and form the 

 whole, except perhaps the top, of the hill between 1ST ant Arddau and 

 Nant-y-gro ; and here a very complete section may be seen along 

 the road from Nantyr to Glyndyfrdwy. The lower beds are ex- 

 posed at the head of the tributary valley immediately west of this 

 hill, in an old quarry in which characteristic Orthoceratites occur. 

 On the side of the hill a little above this, M. colonus occurs in 

 the debris of a trial-working ; and immediately above, along the 

 Nantyr road itself, the flags are well exposed. They consist of slaty 

 beds with thin, hard, siliceous bands. Here and there the siliceous 

 bands become more numerous, and at one point there is a bed of 

 platy grit which is at least 20 feet thick. The dip is between north 

 and east, and becomes more easterly as we proceed towards the 

 north ; but in general the beds dip in the direction of the road at a 

 higher angle than the road itself, and thus the road cuts into higher 

 and higher beds of the series, as it slopes down the hill from south 

 to north. 



All along the road, from a little north of the watershed to a point 

 •east of the farm of Ty'n-y-graig, Monograptus colonus occurs at 



