INTRODUCTION. XXili 
of common species, and some of those belong to types which are not confined to the Lower 
Palzozoiec Division. 
The whole Silurian Series of Westmoreland is overlaid by unconformable and discon- 
tinuous masses of red conglomerate ; generally of very coarse structure, but sometimes passing 
into red sandstone. These masses are the degenerate representatives of the Old Red sandstone. 
Among the imbedded pebbles we find both Cambrian and Silurian fossils; and on the upper 
surface of the older rocks (whether Cambrian or Silurian) on which the conglomerates rest, 
are remarkable examples of mechanical abrasion. 
Il. Middle Paleozoic Division. 
Devonian Series or Old Red Sandstone. 
(1) In Herefordshire and South Wales. 
i) Cornstones croup). oi ererets «le -ley ire Cephalaspis, &e. 
2. Red sandstone and conglomerate . . . Holoptychius, &e. 
The aggregate thickness eight or nine thousand feet. 
(2) In Devonshire and Corniall. 
_ 
. Liskeard or Ashburton group. 
-a. Great Devon limestone. 
J 6. Caleareous slates. 
le Coarse red sandstone and flagstone. 
j Coarse roofing slates and quartzites; ending in North Devon, with beds of red, 
3. Dartmouth slate group . \ green, and variegated sandstone; analogous structure in South Devon. 
bo 
. Plymouth group ..... 
ns 
. Petherwin (or Barnsta- ; a. Marwood sandstone, 
ple) seroupeeien)seretet: | 6. Petherwin slate and C/ymenia limestone ; Calcareous slates of Barnstaple. 
The aggregate thickness of this series is very great, but is not computed. 
In Devon and Cornwall the above series has no base; and we are without any evidence 
as to the beds which are below the lowest Devonian group. Hence there is much uncertainty 
in the co-ordination of the series of Herefordshire with that of Devon and Cornwall: for the 
Herefordshire cornstone has characteristic Fishes without characteristic Shells and Corals; 
while the Devonshire and Cornish series has characteristic shells and corals, but is without 
fishes. 
In a former scheme* the Liskeard and Plymouth groups were united; but they may, 
I think, be conveniently separated. The Herefordshire fish-beds (Cornstone) I had formerly 
placed over the Plymouth group, on the understanding that certain supposed Fish-beds of 
Cornwall were probably of the age of the Dartmouth group. But the Cornish Fish-beds 
* Advertisement to the Second Fasciculus of the Cambridge Paleozoic Fossils. 
