Chap. III.] 
LINGULA-FLAGS OF WALES. 
41 
.T3 
3 
tn 
e6 o> 
E. Davis in 
genus found 
into the superior strata, that no boundary-line 
can possibly be drawn upon a map, between the 
rocks composing the Stiper Stones, and the hard, 
grey, arenaceous, flag-like shale into which they 
graduate, — the latter, too, containing organic 
remains, some of which belong decidedly to the 
| Llandeilo formation. (See ' Silurian System,' 
| pp. 268, 270, 274, 280, 283 et seq., and pi. 32. 
1 figs. 1, 2 & 3.) 
^ The special Lingula of the Stiper Stones has, 
% it is true, been detected in numerous small frag- 
| ments only ; and, whilst the lower beds in the 
| eastern escarpment unquestionably occupy the 
j| same stratigraphical position as the Lingula-fiags 
A of Wales, yet, judging from the fragments, it 
j? appears that the species of the Stiper Stones is 
M not the prevalent Lingula Davisii of the Welsh 
J3 slates. When, however, we recollect the extent 
* to which the strata of the Stiper Stones have 
S been altered, and the rarity and broken con- 
$ £ dition of the Lingulae detected in them, the 
23 specific difference of the one as yet met with is 
■g perhaps of no great importance ; for, as we shall 
| presently see, there are, in Wales, other forms 
* of Lingula associated with L. Davisii. 
^ It is here, also, to be borne in mind that the 
& Stiper Stones are not less than sixty miles dis- 
- tant from their equivalents near Tremadoc, and 
that the deposit has changed its character, be- 
coming much more sandy. The plain facts, how- 
ever, are, that a Lingula-zone in Shropshire, as 
in Wales, lies conformably upon the Cambrian 
or Longmynd rocks, and in both tracts, as will 
a soon be shown, gradually passes up into beds 
«?§ charged with the same Lower Llandeilo species 
3 of organic remains. 
a Lingula-fiags of Wales. — The LingulaB which 
particularly characterize this zone were for a 
long time unknown even to Professor Sedgwick, 
who had described the position and mineral cha- 
racter of the slates in which these fossils occur. 
They were first discovered near Tremadoc by Mr. 
1845 ; and, from their general similarity to some forms of the 
abundantly in well-known Silurian rocks, he then termed the 
