SILURIAN ROCKS OF NORTH WALES. 151 
fossiliferous calcareous beds of Pontyralltgoch, which I would 
refer to a much lower horizon than the top of the Denbigh Grit. 
My object in this communication is not however to attempt to 
draw a map of the Silurian of our District, but to offer some 
more traverses along which, I think, I have established the 
sequence, and where I am able to offer a correlation in which 
may be found some useful base lines for those who have time 
and opportunity to pursue the investigation, and the section I 
particularly wish to illustrate is that across the Clwydian Range 
nearest to Chester. 
Fic. 1. 
At the North-east end of the Section is the sand and gravel 
of the Clwydian Drift (c.p.) resting on Mountain Limestone 
(m.L.) On the South-west of the River Chwiler the Nantglyn 
Flags are turned sharply over into the valley as if near a fault. 
F.a. Represents the Nantglyn Flags which, under the N.E. flank of 
Moel-y-parc, consist of blue mudstone, weathering yellow, 
with the cleavage constantly vertical across undulating beds, 
and splitting into slabs about } inch thick. These are well- 
seen between Nannerch and Moel Arthur. 
Zc, 2. Thin beds of grey tough sandstone with more shaley partings 
and lines of gingerbread coloured rotten stone with fossils. 
Zc. 1. Finely but irregularly laminated sandy shale becoming flaggy. 
Eb. 2. Flaggy, dark and light-grey sandstones, with tracks and 
Graptolites. There are some very massive beds, and some 
curious, crinkly, or knobbly surfaces, like those seen on slag 
or Java, and due to concretionary action accompanying 
pressure-moulding of the rock. These beds are well seen 
West of Moel Arthur. 
£b. 1. Light-grey concretionary sandstones with bands of rotten stone 
full of casts of fossils. 
£.a. More flaggy beds of grey sandstone. 
Clwydian Drift (c.D.) lying irregularly on New Red (N.R.) 
The highest beds of which I have any knowledge in that 
district are the sandy mudstones seen in quarries and numerous 
out-crops close to the Grove, east of Bodfari. The place of 
these beds in the section is fairly clear. They pass down into the 
shales, mudstones, and tough sandstones, which occupy all the 
western slope of Moel-y-parc. They consist of dark lead-grey 
sandy mudstones in which the iron is here and there oxidized 
so as to give a rusty appearance to the rock. Fossils are 
numerous in certain bands, and from them I have obtained the 
following species :— 
Favosites fibrosa Strophomena rhomboidalis 
Atrypa reticularis Pterinea retroflexa 
Orthis elegantula | Holopella 
Rhynchonella nucula Bellerophon 
Spirifera elevata / Orthoceras 
This list does not prove anything with certainty, but the 
stratigraphy of the whole district suggests the correlation of 
these beds with the Tebay Mudstones. 
