200 T, RUDDY ON THE CAMBRIAN AND 
15. On the Upprr Parr of the Camprian (Sedgwick) and Base of 
the Strurran in Nortn Wares. By Mr. THomas Ruppy. (Read 
June 19, 1878.) 
[Communicated by Prof. T. McK. Hucuzs.] 
In the following paper it is proposed to describe in detail some 
sections in the neighbourhood of Corwen and Bala, pointing out the 
fossils which in that district characterize the different zones of the 
upper part of the Cambrian and the lower part of the Silurian. 
The sections are not drawn to scale, being merely diagrammatic 
to show the sequence in each locality. 
Szcrion I. (fig. 1).—On the southern shore of Bala Lake, the rocks 
jutting out of the side of the hill consist of rubbly shale with a general 
dip to the south or south-east. Near the brow of the hill we find 
what is called an ash-bed of no great thickness, but well known in 
the neighbourhood, as it is quarried for building-purposes. In the 
shales immediately above this ash-bed, near Bala, we have the true 
zone of Orthis alternata (Section I., bed 3). When searching for 
this zone on the north of Bala at Fronderw, I was informed by the 
farmer that he had removed an outcrop of rock which interfered 
with his ploughing. The stones he used for building a wall, and 
on examination I found the face of the wall covered with Orthis 
alternata. Associated with it were Orthis elegantula, a few 
specimens of Orthis flabellulum and O. vespertilio, Beyrichia com- 
plicata and Illenus Davisii; this last species and a few others we 
find in every zone. 
The Orthis-alternata zone rises again in the Berwyns. Near 
Milltir Gerrig, on the Llangynog road, the upper felspathic ash-bed 
crosses the road. Above this we find rubbly shales, then a brecciated 
ash-bed twenty feet in thickness, and above it shales in which 
Orthis alternata is again abundant. Associated with it I got Orthis 
elegantula, Leptena sericea, Beyrichia complicata, Nebulipora lens, 
Fuvosites fibrosus, Modiolopsis modiolaris, and Cythere umbonata ? 
Above the limestone (No. 6) there is a great thickness of shale 
(No. 7) varying much in character, in which we find but few traces 
of fossils until we get near to the place marked Bwlch Hannerob, 
where, about 3000 feet above the Bala limestone (see Mem. Geol. 
Surv. vol. ii. p. 86), we find a bed of grit or sandstone, from 15 to 20 feet 
in thickness, with occasionally small calcareous concretions. In the 
grits and in the hard blue shales (Nos. 8, 9, 10, 11) there are plenty 
of fossils, but these are confined to a few species. In a little quarry 
recently opened I found those in the list appended to fig. 1, which proves 
this series to be the equivalent of the Hirnant Limestone. Above the 
hard blue shales and grit we find fine soft blue slates, which im- 
mediately underlie the Tarannon shale (No. 13); but I found 
no fossils here until I had got to the base of the Wenlock series 
(No. 14), where there are plenty of Graptolites. In a quarry very 
recently opened for building-purposes, on the Palé estate, near the 
