88 
SILURIA. 
[Chap. V. 
There are other fossils which occur in "both the Lower and Upper Llandovery 
rocks, such as Leptsena sericea, Orthis reversa, Rhynchonella furcata, R. angus- 
tifrons, Raphistoma lenticularis, Holopella cancellata, Petraia subduplicata, and 
P. elongata. The chief character, however, which unites the lower and upper 
members of this formation, besides the community of these and other species, is 
the great abundance of Pentamerus, Atrypa, and Petraia, — and the absence of 
all, or nearly all the characteristic Trilobites of the subjacent deposits. 
The upper member of the group, c, as seen on the summits and slopes of the 
hills of Noeth Griig and Cefn-y-garreg, has always seemed to me (even in my last 
close reexamination in 1856) to form the regular and conformable capping of the 
lower strata, b. In it we not only find the continuance of the same lithological 
character and colour of the hard, gritty stone, but also the same distinguishing 
fossils, the Pentameri, of which Pentamerus oblongus becomes much more abun- 
dant and characteristic, though still accompanied by P. undatus and P. lens (see 
PL VIII.). Figures of the other fossils of this zone, including the Atrypa hemi- 
sphserica, A. reticularis, Bellerophon trilobatus, Encrinurus punctatus, and Pe- 
traia subduplicata, will presently be given in describing the range of these Upper 
Llandovery rocks through Shropshire and other tracts, where these types are as- 
sociated with Upper Silurian fossils. 
Upper Llandovery Rocks in Radnorshire. Shropshire, Herefordshire, the 
Malverns, fyc. — In quitting the typical Llandovery tract, and in proceeding 
to the N. and E., or to the S.W., the Geologists of the Survey have every- 
where observed a marked absence of the lower member of the Llandovery 
rocks, and have ascertained that the upper zone with Pentamerus oblongus 
is alone present, and forms the natural base of the Upper Silurian rocks. 
Thus, in Radnorshire, this upper zone is represented by a thin course or 
two of sandstone or conglomerate, occasionally resting, as near Builth, in 
striking unconformability on the upturned edges of the Llandeilo flags. 
That tract, it will be remembered, like the district of Shelve and Corndon 
in Shropshire, is replete with igneous rocks ; and, in both, the Llandeilo 
formation appears to have been raised from beneath the waters, and not to 
have been depressed or again subjected to any marine action during the 
whole period when the Caradoc formation was accumulating. Such rela- 
tions are strikingly exhibited in the diagrams already given at p. 50. 
In tracing the relations of the Caradoc sandstones of Shropshire to the 
overlying shale and limestone of the Wenlock Edge, I was formerly led to 
believe in the existence of an unbroken ascending series. This appeared 
to be the case on the banks of the Onny, where that river flows from Hor- 
derley on the N.W. to Wistanstow on the S.E. I then saw that the lower 
beds of the Caradoc formation were highly inclined in the proximity of the 
igneous rocks of Caer Caradoc, but that the inclination decreased gradually 
to the east, so that the flagstones of Cheney Longville, which were de- 
scribed in the last Chapter, seemed to pass with apparent conformity under 
those beds of shale and limestone which contain Pentamerus oblongus. 
Now, as I had found this same characteristic fossil in strata of South 
Wales which graduate downwards (as already shown) into rocks with 
