CAEADOC BEDS IN SOUTH WALES. 
73 
portion of the Caradoc formation is omitted, the 
hilly tracts to the north and west, i.e. on the 
"g" right bank of the stream, which had been called 
% Cambrian, afforded clear indications of a gradual 
| and conformable upward passage from the Llan- 
g deilo Mags into schistose beds. These, becoming 
11 more arenaceous and siliceous as they rise into 
o, higher hills, contain some calcareous courses, the 
8 fossils of which are all identical with those of 
CO 
g the Caradoc and the Bala rocks. 
m This section (published on a much larger scale 
g by the Survey) was made, in the year 1842, by 
r| Professor Ramsay. The fossils he then collected 
Z and sent to London were examined and deter- 
0 mined by Mr. Salter. 
g The great mass of the strata above the Llandeilo 
3 ^ Flags, as seen in ascending the Nant-y-Rhibo Brook 
to Cwm-y-gerwn, consists of dark sandy shale with 
some calcareous matter, containing the following fos- 
| pj sils, all of which are of true Caradoc age : namely, 
§ o Trinucleus seticornis, His. ; Staurocephalus Murchi- 
1 -2 soni, Barr. ; Orthis insularis, Eichw. ; O. Actonise, Sil. 
^ Syst. ; 0. vespertilio, id. ; 0. calligramma, Dalm. and 
qq Sil. Syst. ; Leptsena trans versalis, Dalm. L. quinque- 
I costata, M'Coy; L. tenuicincta, id. ; Cyclonema cre- 
00 ^ bristria, id. ; and the Chain-coral. Proceeding to still 
Jf ]d higher ground, extending to Mynydd banc-y-ffair, we 
meet with other forms ; for, while there are still a few 
o 
B B 
% Caradoc fossils, such as Orthis crispa, M'Coy, and the 
j6 Ph remarkable Trilobite Encrinurus multisegmentatus, 
J! o Portlock, these are associated with the Atrypa reti- 
cularis, a shell which uniformly characterizes the 
higher zone to be presently described under the name 
^ of Llandovery Rocks. Again, the highest beds visible 
* in this line of section indicate still more clearly a 
passage into the Llandovery rocks. Thus in them 
o we detect the Atrypa crassa, Leptsena transversalis, 
a Rhynchonella closely resembling R. navicula, and 
Jj a large Heliolites, all unknown in the inferior or true 
£j Caradoc strata, one of the fossils of which, however 
° (Orthis insularis), still remains, as if to demonstrate 
0 a gradual zoological transition. 
^ On the left bank of the Towy, in the wooded grounds 
^ of Llandovery, we again find the Llandeilo beds regu- 
P larly surmounted by slaty and arenaceous beds, which, 
* It was this section (as before stated) which led Sir H. De la 
Beche and Professor Kamsay to abrogate the hypothetical line for- 
merly drawn between the known Silurian country and the tracts 
unexamined and unknown by me. 
