102 
SILURIA. 
[Chap. V. 
rocks, and thus display a transition from the inferior strata of which we 
have taken leave, into those overlying deposits whose structure and con- 
tents we are about to consider. 
In illustration of the conformity to the Lower Silurian of those Upper 
Llandovery rocks which were formerly classed with the Caradoc Sandstone, 
but were subsequently determined by their organic remains to pertain to 
the base of the Upper Silurian, three sections are here offered. 
In the first edition of this work, certain sections and their descriptions, 
as taken from the publications of the Geological Survey, though perfectly 
correct in delineating the physical data, required a different terminology. 
On the revision of a large region of Wales by Mr. Aveline, under the 
direction of Professor Eamsay, the following points were readjusted. In the 
first of these diagrams, the title was changed from ' Llandeilo schists 
supporting Caradoc sandstone,' into " the Caradoc formation («), supporting 
Tarannon shales (b) and Denbigh grits {c)," — the last-mentioned being 
known to contain Wenlock fossils, and therefore classed as Upper Silurian. 
Caradoc or Bala Formation supporting conformably the Tarannon Shales and 
Denbigh Grits. (Horiz. Sect. Geol. Survey, ]S T o. 35.) 
, Sir W. Wynne's Mynydd ^ , ~ 
W. by JN, Monument. Mynyllod. b J 
a * * b c b * 
a. Caradoc or Bala formation with thin courses of limestone, b. Tarannon shales or 
pale slates, c. Denbigh grits and shales of Wenlock age, lying in perfect conformity 
on the pale slates. 
The slaty cleavage is partially represented by white lines. The dark traversing lines 
are faults, *, whereby the Upper Caradoc beds are lost. 
In this rectification the reader will see how important is that separation, 
of the Caradoc (Bala) from the Landeilo formation, which has been so 
fully explained in the preceding pages. 
In the next section, the lowest beds visible are simply the Tarannon shales 
Borders of Eadnor and Montgomery. (Horiz. Sect. Geol. Survey, No. 27.) 
N.W. S.E. 
b b 
b. Tarannon shales or pale slates. <?. Denbigh grits, with grey and blue schists. 
