52 
SILUEIA. 
[Chap. HE. 
Some of these fossils, e.g. Angelina, together with Lingulella Davisii and 
L. lepis, were found by Mr. Salter in the lowest beds of the zone ; and 
these he thinks may be more accurately classed with the upper portions of 
the Lingula-flags. Ogygia scutatrix, however, found in them, is of a genus 
as yet unknown in rocks lower than the Llandeilo Flags. 
The chief mass of the Llandeilo formation is not well seen around the 
bases of Snowdon and Cader Idris as surmounting the older strata or Lin- 
gula-flags. Stratified igneous rocks with slates are there so dominant 
throughout a vast thickness, that the type-fossils, such as Asaphus tyrannus 
and Ogygia Buchii, have not yet been detected, although some associated 
species of shells occur rarely. • 
On the eastern flank, however, of the Berwyn Mountains, just as at 
Llandeilo in South Wales, the formation, though slaty, is characterized 
by its organic remains, and is seen (Section, p. 60) to pass under other and 
more arenaceous rocks which form the mass of the Caradoc formation, with 
which the limestone rocks of Bala in North Wales have been identified. 
The clear separation of the Llandeilo from the overlying formation of Bala, 
with which it was formerly associated, will be dwelt upon in the sequel. 
In the Shropshire district, where the fullest examples of the lowest Silurian 
deposits are exhibited, the reader will see, by reference to the coloured 
Map, that the Llandeilo formation is subtended on the north, south, and 
west by younger Silurian deposits, with which the older rocks are abruptly 
collocated. To this break, as well as to other discordances of position, 
attention will be called in other Chapters, it being now desirable to 
conduct the reader to spots where he may clearly see that the flags con- 
taining Asaphus tyrannus, together with Graptolites and other fossils, and 
identical in their contents and character with the strata of the Shelve tract 
in Shropshire, are conformably overlain by masses usually more arena- 
ceous, which represent the great body of the Caradoc (or Shelly) Sandstone 
of the Silurian classification. 
In South Wales, the same ascending order that we have followed from 
the western flank of the Longmynd and in North Wales has been observed, 
and must be here noticed. 
In the environs of St. David's, as before said, purple and green schists 
and hard grits, long ago identified with the rocks of the Longmynd, and 
containing traces of so-called Fucoids *, are overlain in Whitesand Bay by 
slaty flagstones (see Map), in which Lingulella Davisii occurs with many 
Trilobites (collected by Mr. H. Hicks f ). It is in this tract that the connexion 
of the lowest formation of the Silurian System, or the Lingula-flags and 
Tremadoc slates, with the Lower Llandeilo is better seen perhaps than in 
any other part of Wales or England ; for here the bluff cliffs, as seen in a 
beautiful coloured sketch by Mr. C. R. Aston, exhibit a continuous and united 
succession of dark slates and schists, in which it is as impracticable to 
* Sil. Syst. p. 39. t See Fossils, Chap. IX. 
