SILURIAN ROCKS OF NORTH WALES. 149 
Coniston, there are higher shales (Ashgill Shales) of the under- 
lying series remaining and the basement bed is represented by 
a thin calcareous band. 
Above the basement beds the Graptolithic Mudstones, Pale 
Shales, and various sub-divisions of the Coniston Flags come 
on, and though all the Graptolite zones cannot everywhere be 
detected, that is probably in most cases owing to obscured 
sections or insufficient time devoted to the search, seeing that, 
when found, their order of succession is constant. Also the 
lenticular limestones at the base and the sandy horizons in the 
lower part of the Coniston Flags are not, from the nature of 
the case, to be expected in every section. 
Section D. 
In the Craven District there is still much variation among the 
basement beds, but a great similarity when we examine the 
higher members of the Series. I will take as my type the 
section seen up Austwick Beck. The Carboniferous Rocks with 
pockety patches representing the Devonian can here be seen 
resting almost horizontally on the up-turned edges of the 
Silurian and Upper Cambrian (Ordovician) Rocks. It is one 
of the most marked and most remarkable unconformities in the 
world. ‘The uppermost beds of the Silurian are nowhere seen 
in this area. The highest that has escaped denudation is the 
Studfold Sandstone, quarried near a farm of that name, east of 
the Ribble between Settle and Horton. This is seen to rest on 
the flags of Arco Wood, the equivalent of the Leck Beck Flags 
and of the upper or main mass of the Coniston Flags. A massive 
unfossiliferous grit, which I have described as the Austwick 
Grit, separates these from the Austwick Flags below which 
pass down into red shale and these into pale slates in the lower 
part of which the zones of the Graptolithic Mudstone are 
represented, but here we find a band of Limestone in which 
Mr. Marr detected the characteristic Phacops elegans, and at the 
base of this clear and variable series there is a strong 
conglomerate separating the basement beds of the Silurian 
from the Bala Shales and Limestones. 
There is another important section a few miles further up 
the valley where a fold brings up the Coniston Limestone, and 
the basement bed of the Silurian rests directly on it without 
the intervention of the Z7inucleus and Strophomena Shales. The 
basement bed here itself consists of a brecciated concretionary 
limestone with a different group of fossils from that in the 
underlying Coniston Limestone. Here we have the same kind 
of difficulty as we shall see arises at Aberhirnant. 
SEcTION E. 
Now we are in a position to examine the Sections of North 
Wales, with a knowledge of the sequence in the adjoining areas, 
