480 W. J. SOLLAS ON THE SILURIAN DISTRICT 
It will be seen from this list that the beds belong to the Wenlock 
series, though they have very much of a Llandovery facies. The only 
exclusively Ludlow forms are Lingula cornea and Acidaspis coronata ; 
and the determination of these rests on somewhat imperfect speci- 
mens. On the other hand, we may draw attention to the great 
abundance of Petraia bina and Enerinurus punctatus, together with 
Leptena transversalis, and the occurrence of Leptena sericea. I do 
not mention Murchisonia pulchra, because its determination is some- 
what doubtful ; nor Pentamerus oblongus ; for though a fine specimen 
of this shell was found in the quarry by one of my students, I have 
not been able to find one myself, and had the misfortune to lose the 
single specimen which was presented to me. I think, however, that 
it will be generally allowed that, while the beds are probably 
Wenlock, they must yet be assigned a position near the base of the 
series. 
The next highest beds in the series are to be found in the ditch 
on the left-hand side going up Pen-y-lan lane. They consist of 
hard siliceous grits and soft mudstones. Leaving these we turn 
down a lane running parallel with and immediately north of the 
word ‘“‘ Pen-y-lan” on the map, again turn out of this to the left, 
into a narrow path leading to a farm: here, in a small cutting, we 
find red or claret-coloured fine argillaceous sandstone, striking 65° 
W. of N., and dipping at an angle of 27° to the north. These beds 
are quite unfossiliferous, and closely resemble many parts of the Old 
Red Sandstone. 
A little further, and we come to a quarry cut in a hard siliceous 
grit, which may be better studied on the other side of the Rhymney, 
and to which we give the name of the “ Rhymney Grit.” 
Crossing now to the Rhymney ridge, which in practice must be 
done by continuing along the turnpike road from Roath towards 
St. Mellons, we first meet with Silurian beds on the right-hand side 
of the river after crossing the bridge over the Rhymney. They are 
exposed only at low tides, consist of greyish mudstones passing into 
argillaceous sandstones, and contain fossils, of which Mr. Ross and 
myself obtained the following species—Petraia bina, Strophomena 
depressa, Encrinurus punctatus, Leptena sericea, and others too frag- 
mentary to determine. ‘The strike, as well as we could make it out, 
is 55° W. of N., and the dip 30° and towards the north. 
These beds, then, correspond lithologically and paleeontologically 
with those of Pen-y-lan quarry, and therefore in all probability 
occupy the same horizon. Indeed, there can be no doubt about this, 
since they occur at just about the same depth below the character- 
istic Rhymney grit, which we shall presently describe. 
Turning now to the left on crossing the bridge, we walk across a 
grass-grown tidal flat to the banks of the Rhymney below Cae 
Castell. Here we meet with a beautiful cliff-section across the 
Silurian beds—only observable, it is true, between tides, and grass- 
grown and inaccessible in places, but on the whole displaying the 
seriesadmirably. The first bed we reach is the Rhymney Grit, which, 
by a rough triangulation, lies about 380 feet above the Pen-y-lan 
