Chap IV.] THE CARADOC FORMATION AND FOSSILS. 
67 
therefore very peculiar, as long ago remarked*, in being the oldest strata 
of Britain which present such a comparatively recent lithological ap- 
pearance — one entirely differing from anything to which the word 
'grauwacke' had ever been applied by geologists. And yet, notwith- 
standing their soft and sectile character, these Caradoc sandstones are 
laden with a profusion of fossils of the same species as occur in the 
hard, slaty, argillaceous rocks of large regions of "Wales, with which they 
were truly identified in a few tracts at the period of the publication of 
the * Silurian System 'f. In short, these shelly sandstones, so near to 
the Wenlock Edge, and so clearly overlain by a full Upper Silurian 
series, form essentially a vast portion of the same great Lower Silurian 
division to which the preceding chapters have been devoted, and whose 
strata in a more crystalline and slaty state are spread over such large 
tracts of Wales. The manner in which this result has been fully worked 
out, amidst the difficulties of so complicated a region, is one of the 
greatest triumphs of my successors in that diversified Silurian field. 
A great thickness of these shelly sandstones is exposed in the sides 
of the steep lanes leading down from the ridge of Enchmarsh and Chat- 
well to Cardington, near to the last of which places their uppermost or 
flag-like finely laminated courses (e) have been laid open at Gretton. 
There a vast abundance of characteristic fossils have been obtained; 
nearly all of them being forms equally well known in the Bala rocks of 
North Wales. These beds (e) were formerly designated ' Cheney Longville 
flags,' from their being well exposed at the hamlet of that name on the 
right bank of the River Onny. They graduate upwards into earthy 
beds or shales (/), which in this district are laden with the well- 
known Trilobite Trinucleus Caractaci (Sil. Syst.), but for which I after- 
wards adopted the name ' T. concentricus,' previously given to it by 
Mr. Eaton of the United States. This beautiful fossil (figured in PI. IY. 
and Foss. 46) is found from the base to the summit of the formation, 
and was named by me after the old British King and the adjacent 
ridge that still bears his name. Other sections across the strata enu- 
merated may be observed in other traverses of the same distriot. The 
clearest of them, as exposed upon the banks of the Onny, between 
Horderley on the north-west, and Wistanstow on the south-east, was 
given in detail in my earliest work. It is enough to recapitulate 
that the lower of the shelly sandstone masses to which we have been 
calling attention, exhibiting courses of calcareous grit ranging from Hor- 
derley to Corton, were described as containing Orthis flabellulum, 0. 
vespertilio, 0. unguis, Strophomena expansa, Crinoids, and Trilobites ; 
whilst the superior beds were said to abound in different Orthidae, parti- 
cularly Orthis Actoniae and 0. grandis, and Trinucleus Caractaci. The 
* Sil. Syst. pp. 216-222. with the Meifod rocks, identified by me with these 
t The sandstones &c. of Welsh Pool, and of the Caradoc Shelly Sandstones (Sil. Syst. pp. 302-307, 
valleys of the Tanat and Ffyrnwy, were, together and pi. 32. f. 9). 
F 2 
