SILURIAN ROCKS OF NORTH WALES. 147 
But the flags and sandstones at the top of the Silurian are 
still left in places as in the district round Kendal, where, on 
Kirkby Moor, we find the Tilestones with their characteristic 
species of Grammysia, and Orthonota, and Pverinea, represented 
by the Kirkby Moor Flags with the same fossils, and the 
underlying Hay and Downton Sandstones represented by the 
Grey Sandstones of the Kendal Group, so well exposed on 
Benson Knot, with the characteristic Holopellas, &c., occurring 
in brown weathered bands exactly as in the Southern Sections 
of Carmarthenshire (A.) Below this series we have in Section Cc 
some 2,000 feet or so of dark blue flags, shales, or slates, known 
as the Bannisdale Slate with few fossils but those common to 
the Ludlow. Then, as seen on the slope of the hill near 
Firbank and across the hill side to the Sedbergh and Kendal 
Road, there isa mass of dark grey sandy shale some 800 or 
goo feet in thickness, having calcareous bands, especially at the 
base and top of the series. Those which I have called Firbank 
Limestones are crowded with, and in fact in places almost made 
up of Rhynchonella nucula and R. navicula, and much resemble 
the Aymestry Limestone of Knell Coppice, near Malvern. Below 
this horizon come the beds which I have named the Tebay Mud- 
stones, from the well-known Railway Junction, close to which 
they are well developed. These last have yielded as yet but 
one Orthis, and that referred by Davipson to a new species. 
Below the Tebay Mudstones are massive Sandstones, which, 
repeated by many a fold and fault, form the bold outlines of the 
Howgill Fells. The fossils of this series have been given in 
the Mem, Geol. Survey, 98 N.E., and hardly justify our 
separating the series from the Ludlow Rocks, especially when 
we take account of the Winder Grit Colony in the lower part 
of the series, immediately north of Sedbergh, in which the 
fossils found together in the same bed have a decided Ludlow 
facies, and on the west of Helm Knot a thin bed of pea-grit 
with the same fossils occurs among the lower beds of the sand- 
stone. At a slightly higher horizon, on the Riggs between 
Helm Knot and Sedbergh, and at High Hollins, as well as at 
the south end of Casterton Low Fell, there is a fossiliferous 
band of great importance for our present purpose. It is 
characterized by a new species of Acdaspis which SALTER has 
called A. Hughesii. This bed is confined to one very limited 
horizon. Its lithological character is not very marked, but yet 
sufficiently distinctive to help one in selecting the rock best 
worth searching for fossils. It isa dark grey sandy mudstone 
breaking into short prismatic fragments, and frequently 
showing a ball and socket arrangement such as might result 
from an incipient conchoidal fracture, helped perhaps some- 
times by a slight concretionary structure (see Mem. Geol. 
Survey, 98 S.E., p. 10; 98 N.E., p. 11.) 
The base of this sandy series is sometimes, as on Helm Knot, 
very fossiliferous, and passes down gradually into the thick flags 
