Chap. III.] 
THE LLANDEILO FOEMATION. 
47 
is also seen to be overlain (unconformably), on the north-west and south- 
east, by a zone of flags containing Lingula Davisii, which is well exposed 
in Whitesand Bay (see Map), — followed on the north-west by black schists, 
flags, and slates, representing the mass of the Llandeilo series. Thus, 
whether we examine North or South Wales, we ascend gradually from the 
same bottom rocks as those of the original Salopian or Shropshire tract, 
through strata which afford the earliest well-defined remains of animal life. 
This great series of Lingula-flags, so well developed in Wales, is the 
zone which, in Bohemia, through the enlightened researches of M. Bar- 
rande, has proved to be the basis of all Silurian life, and which therefore 
received from him the name of " Primordial." It is indeed clear that the 
Fauna of this zone merits all the importance attached to it by its eminent 
founder, since we have now ascertained that, such as he has described 
it, the group exists in America, Scandinavia, Belgium, and Spain, as well 
as in the British Isles and Bohemia. 
Llandeilo Formation in Shropshire and adjacent part of Montgomeryshire. 
— Although this formation obtained its name from the town of Llandeilo 
in Carmarthenshire, where the greatest number of its characteristic Trilo- 
bites were collected, let us first describe it in the district of Shropshire, 
since there is no portion of the British Isles where a clearer exposition 
can be seen of the ascending order from strata containing the earliest 
signs of former life up into deposits teeming with organic remains. The 
subjacent strata which we have been considering do not, indeed, rise to the 
surface at or near Llandeilo ; and hence the description of the formation 
near that town is deferred. 
During my early researches in Shropshire, I observed certain fossils 
within a few hundred paces of the Stiper Stones ; but many more important 
organic remains have been since detected close up to that striking ridge. 
In addition to the clear stratigraphical order which is there exhibited, 
we now indeed possess fossils for the perfect elucidation of each band as 
we proceed upwards from the Stiper Stones to the other Silurian deposits 
(see the sections, pp. 26 & 38). 
The strata into which the siliceous grits of the Stiper Stones graduate 
upwards are slightly micaceous grey flagstones, usually weathering to a 
brownish colour, and alternating with more schistose and darker- coloured 
beds. On the whole they are of uniform texture, as seen in any of the 
deep combes which indent the western side of the ridge of the Stiper 
Stones *. Thus in the transverse opening in Lord's Hill near the Snail- 
batch Lead-mine f , or in the deep hollows of the Crow's Nest, Black Hole, 
Mytton Dingle, and Perkins' Beech, the strata, being scarcely at all inter- 
* See Section at p. 24; and Map of the Geo- the age and sequence of the deposits. The asso- 
logical Survey, Sheets 60 and 61. ciated igneous rocks, however, and the vast inter- 
t The reader who desires to obtain information polated sheets of volcanic grit which begin to show 
respecting the lead-mines of this tract, which oc- themselves very low in the order of the strata, 
cur in these Lower Silurian rocks, must consult and particularly in this tract of Shropshire, will 
the ' Silurian System,' pp. 277 et seq. In this be described in the next Chapter, 
work my chief object is to present a clear idea of 
