Chap. III.] 
OMISSIONS OF CAKADOC SANDSTONE. 
59 
features and rocks similar to those of the grander mountains of North Wales. 
The environs of Builth and Llandrindod, indeed, afforded a very large 
portion of the fossils originally published as typical of the Llandeilo 
rocks *. 
"Whether collected at Wellfield and other places near Builth, or in the 
flagstones north of the Carneddau Hills, Ogygia Buchii, Ampyx nudus, 
Agnostus Maccoyii, and Lingula attenuata are found in abundance, with 
beds full of Orthis calligramma and other characteristic shells. 
Near Builth, however, as in -the west of Shropshire, there is no equiva- 
lent whatever of the Caradoc (or Bala) formation. This omission is ex- 
plained in these two sections, taken from the publications of the Survey, 
which represent the Upper Silurian, with an occasional thin course of 
Llandovery rock, reposing upon the edges of the Llandeilo formation. 
Unconformable Belations of Llandeilo Flags and Upper Silurian Rocks, 
near Builth. 
(From Sections published by the Government Survey.) 
S.E. N.W. 
Gwaun Ceste. Near Tyn-y-Coed. 
e b * b * b * 
b. Llandeilo formation, d. Thin course of Upper Llandovery rocks, the Caradoc (c) 
being absent, e. Wenlock rocks. /. Ludlow rocks. (In the lower section the 
omission is still larger, there being no trace even of the Upper Llandovery rocks.) 
* Trap rocks. 
Again, when we travel westwards from the typical tract in Shropshire 
(see Map), where, as already shown, the Landeilo formation reposes clearly 
on the Stiper Stones, we lose all traces of it until we reach the eastern flank 
of the Berwyn Mountains, the intermediate country being occupied by 
younger deposits, from the Caradoc formation upwards, — thus clearly indi- 
cating that various parts of these regions have been subjected to powerful 
local oscillations, leaving here and there only the unbroken segments of the 
whole series of successive deposits, accompanied by the organic remains 
peculiar to each f . 
* So much importance was attached to the lo- to the Geological Society for 1863, in which the 
cality of Builth, that in an early memoir (Proc. number and importance of the great breaks in 
Geol. Soc. vol. ii. p. 23), I termed the deposit the succession of the Silurian strata of Wales are 
' Builth and Llandeilo Flags.' prominently brought forward and clearly ex- 
t See Professor Kamsay's Presidential Address plained. 
