508 
SILUKIA. 
The Llandeilo Group of rocks, comprising the Lower Llandeilo (or Tremadoc) 
Slates, and the Llandeilo Flags proper, are black, flag-like, and slaty deposits, 
occasionally calcareous, extensively developed at Tremadoc and Ffestiniog in 
North Wales, also in Shropshire, and in South Wales at Llandeilo, Builth, &c. 
They include at their base the dark-grey flagstones and schists which occupy 
the western slopes of the Stiper Stones (see pp. 47 &c). The fossils of these 
two groups are included in the column headed ' Llandeilo.' 
In the i Caradoc ' column are included all the rocks of the Caradoc sections of 
Shropshire, the Bala Limestone, and the arenaceous beds above and below it, all 
which beds overlie the black slaty Llandeilo series in North and South Wales 
(see pp. 63 &c). The fossils of Snowdon, of Coniston in Westmoreland, of 
Ayrshire, Tyrone, Dublin, Waterford, Wexford, &c, are also included in this 
division. 
The fossils of the Lower and Upper Llandovery rocks are included in one 
column (' Llandovery'), because they constitute an intermediate group; but the 
reader will see in the text that I have clearly indicated their distinction, showing 
that the Lower Llandovery rocks unite naturally with the Lower Silurian, and 
the Upper Llandovery with the Upper Silurian. (See also the Legend at the 
side of the Map.) 
The Woolhope Limestone and the Denbighshire Grits are here regarded as 
the lowest portion of the Wenlock rocks ; and the ' Coniston Grits ' of Professor 
Sedgwick with their few fossils are included in the same group. The fossils of 
the Bog-mine, near Shelve, Shropshire, are also thus placed, as they are Upper- 
Silurian species. 
The ' Ludlow ' column embraces the Lower and Upper Ludlow rocks and the 
intervening Aymestry Limestone ; whilst the term ' Passage-beds ' refers to that 
thin band (' Ledbury Shales' of Salter) which exhibits a passage from the 
Upper Ludlow to the Old Red Sandstone, — the Downton Castle Sandstone 
being retained with the Ludlow rock proper (pp. 135 &c). 
[In the following List, references are made to the Woodcuts of Fossils in the text, and 
to the Plates at the end of the work, in a distinct and darker type.] 
PLANT iE f. 
Actinophyllum plicatum, Phil. M. G. S. ii. p. 386 
Chondrites verisimilis, Salt. M. G. S. Expl. Sheet 
32. pi. 2. f. 1, 2 
Fucoides. Foss. 16. p. 96 
Pachytheca sphserica, Hooker. PI. 35. f. 30 . . . 
Spongarium aequistriatum, M'Coy, Pal. Fos. p. 42 
Edwardsi, Murch. PI. 12. f. 3 
mterlineatum, M'Coy, Pal. Fos. p. 43 ... 
interruption, M'Coy, Pal. Fos. p. 43 ... 
t The nature of some of the fossils under this head is 
doubtful. 
II 
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Ph 
bp 
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