124 
SILURIA. 
[Chap. VII. 
convey an adequate idea of the succession. (See also Map, and Section 
beneath it.) 
Section across the Ludlow Promontory *. 
(From Sil. Syst. pi. 31. f. 5.) 
mm. 
f # e* e 
d 1 . Wenlock shale, d 2 . Wenlock limestone. e\ Lower Ludlow beds. e 2 . Aymestry 
or Ludlow limestone, e 3 . Upper Ludlow beds. /. Old Red Sandstone (bottom beds of). 
In following the formation from the Ludlow tract on its strike or direc- 
tion to the S.W., its included limestone, like that of the subjacent deposit, 
is also soon seen to thin out and disappear. Scarcely has the geologist 
quitted the north-western corner of Herefordshire, than he finds the cen- 
tral band attenuated to a mere course of calcareous grit, which is entirely 
lost in Badnorshire. There the Upper Silurian rocks of the mountain of 
Badnor Forest, which are laid open in the ravine of £ Water-break-its- 
Neck ' and other gullies, expose a gradual succession from the Wenlock 
through the whole of the Ludlow formation up to the junction-beds of the 
Old Bed Sandstone, and with scarcely a trace of limestone. As such also 
the formation ranges for the most part through Brecon and Carmarthen, 
the central part being nowhere a workable limestone, and only here and 
there calcareous, except through the occasional presence of a few testaceous 
remains. In Marloes Bay, Pembrokeshire, where the Silurian rocks are 
exposed in the sea- cliffs (see the view at the end of this chapter), it is dif- 
ficult to say more than that sandy calcareous shale and very impure lime- 
stone containing Wenlock fossils are surmounted by ferruginous and hard 
sandstone, rarely calcareous, and in parts a conglomerate. 
In the Clyro and Begwm Hills, however, or along the eastern frontier 
of the Silurian rocks, extending from Kington towards the south-west, the 
Ludlow rocks retain much of their typical characters, and particularly 
on the banks of the Wye, between Builth and Hay, where I first ob- 
served their relation to the Old Bed Sandstone. (See Map and Sil. Syst. 
p. 312.) 
Let us now consider the nature of the different members of the Ludlow 
formation, where they are most conspicuously characterized by the greatest 
quantity of fossil remains. 
Lower Ludlow Rocks. — These strata, which are, I repeat, simply an up- 
ward prolongation of the Wenlock formation, are composed of dark-grey 
shale, rarely micaceous, with small concretions of impure limestone. My 
* Like the Woolhope Valley and all of the so- between G-atley and Whiteway Head, are entirely 
called Valleys of Elevation, including the grand denuded and swept clear of. all debris, foreign 
tract of the Wealds of Sussex, Surrey, and Kent, or local, 
this Valley of Wigmore, and the lateral valley 
