694 PROF. T. MSKENNY HUGHES ON THE SILURIAN 
53. On the Strurtan Rocxs of the Valley of the Cuwyp. 
By Prof. T. M‘Krenny Hueues, M.A., F.G.8S. (Read May 14, 1879.) 
Iy the following paper I offer a preliminary sketch of the Silurian 
rocks of the southern and western part of the Valley of the Clwyd, 
and an attempt to correlate the details with the sequence established 
elsewhere. 
In the northern part of the district flaggy shales with subordinate 
more sandy beds occur; and though fossils are abundant at various 
horizons, I could not detect any group so marked that I could easily 
trace it across the country in the limited time at my deposal, while 
the endless rolls and folds made it difficult to determine, even 
within short distances, which were higher and which lower beds. 
A full list of the fossils of Llansannan from ‘“ beds above the Denbigh 
grits ” is given by Salter, Mem. Geol. Survey, vol. iii.; but I think it 
will be found that there are two horizons, both well up in the Denbigh 
beds, at which Grits occur, and that the Llansannan fossiliferous beds 
occur between them. 
At Pontyrddol, a little over three miles W.S.W. of St. Asaph, 
I procured the following fossils in a black and grey flaggy sandy 
shale :—Petraia sp., Encrinite stems, Atrypa reticularis, Chonetes 
lata, Leptena minima ?, Orthis elegantula, Orthis, sp. (var. of ele- 
gantula), Rhynchonella navicula, Spirifera elevata, Strophomena 
depressa, Pterinea retroflexa. 
On Moel Fodia, about three miles to the south, the beds are very 
fossiliferous; I obtained the following from various sma]l openings 
near the top of the hill :— 
List of fossils from Upper Denbigh Flags of Moel Fodia, Denbigh. 
Cliona prisca. Spirifera crispa, His, 
Nebulipora (Monticulipora). elevata, Dalm. 
Favosites fibrosus, Goldf. Strophomena funiculata, M/*Coy. 
Crinoid stems. depressa, Dalm. 
Lichas, sp. Leptena transversalis, Dalm. 
Atrypa reticularis, Lznn.?, var. with | Cardiola interrupta, Brod. 
fine lines. Cucullella antiqua, Sow. 
Meristella, sp. Pterinea tenuistriata, M‘Coy. 
Rhynchonella navicula, Sow. imbricata, n. sp. 
nucula, Sow. Cyrtoceras. 
Orthis elegantula, Dalm. Orthoceras primevum, Forbes. 
West of Denbigh similar beds can be followed rolling into the hills, 
the Encrinite flags of Nantglyn being apparently pretty high in the 
series. South of Llanrhaiadr and of Llywesog even-bedded banded 
flaggy shales are seen at intervals here and there all the way up to 
the gritty sandstones of Ffriddfawr ; and in the next valley there is 
a very clear descending section from Caregygath, near Moel Ganol, 
by Cyffylliog along the Clywedog into the Vale of Clwyd. 
On the top of Ffriddfawr (see fig. 1) opposite Moel Ganol we find 
a pale grey sandy mudstone, massive were it not for cleavage, with 
the bedding generally obscure. Under this are grey tough beds of 
