SILURIA. 
[Chap. III. 
p flags of this age, often highly altered, again 
& prevail. With the loss of calcareous matter, 
g however, the schists of Llanwrtyd no longer 
% exhibit the characteristic Trilobites and 
| Shells of the formation, though they contain 
g some Graptolites. There the beds are so 
| slaty and crystalline that the highly in- 
g clined cleavage of the slates, as represented 
* in the foreground of the preceding sketch, 
< is the only feature visible to the unpractised 
g p4 * eye, — the real strata undulating or dipping 
^3 at a much less angle, as represented in the 
| § sloping bank on the left of the foreground of 
gj the drawing. 
o 
When viewed, however, on the grand 
scale, there is no district more explanatory 
of the general succession than this very tract 
between Llandovery andBuilth,of which the 
g | J, vignette at p. 57 represents a part. There, 
rt I r-; if the spectator stands on the summit of the 
h o ^ mountain of Esgair Davydd (b), above the 
§ I -| Baths of Llanwrtyd, he overlooks a wide area 
s| | to the south-east, and has beneath his feet, 
°„ 5 T» and for a certain distance before him, a mass 
8g | of the lower slaty rocks (a) now under con- 
es *1 8 sideration : whilst in the dull round hills of 
« | a the middle ground are spread out the Upper 
I E r Silurians of the Mynydd Epynt andMynydd 
P3 !z; 
% n Bwlch-y-Groes, as in this diagram. In the 
background, the Old Red Sandstone is seen 
occupying parts of the Mynydd Epynt, and 
o> g thence rising into the Pans of Brecon and 
k § Carmarthen, the highest mountains in South 
x > m Wales, — the latter 2860 feet above the sea. 
% In the hilly district extending from Builth 
§ on the Wye to Llandrindod and Llandegly 
J (see Map), the Llandeilo formation again 
U rises to the surface in the form of a rugged 
sjj ellipsoidal mass, throughout which igneous 
9 rocks, both stratified and eruptive, prevail, 
a In the sequel it will be shown how that 
§ tract, as well as the district of Shelve (both 
S originally described in the 4 Silurian Sys- 
tern'), presents to the geologist physical 
