40 
SILURIA. 
[Chap. III. 
shale, and the lower dividing lamina? are here and there composed of 
greenish and white nnctuons clay*. 
On the surface of some of the numerous flag-like beds are broad wavy 
undulations, and also the ripple-marks so common to many sandy deposits. 
Together with these are also ramose and twisted forms, some of which are 
possibly the casts of Seaweeds, whilst others, such as the Chondrites, 
M'Coy, and Cruziana, d'Orb. (Bilobites, Cordier), may be due to the trails 
of Annelides, or to the burrows and galleries made by Crustaceans. 
Mr. Salter has satisfied me that some of the more tubular cavities 
and cylindrical bodies are the borings and casts of worm-like animals, 
and may well, represent the Scolithus linearis described by the eminent 
American palaeontologist James Hall, — a fossil which characterizes the 
Potsdam Sandstone, or lowest Silurian rock of North America. The ver- 
tical tubes, curved at their base, and their trumpet-shaped openings, are 
well preserved, and of a size equal to those made by the common Lob- 
worm on our coasts. These appearances are represented in the accom- 
panying woodcut. 
Numerous fragments of Lingulae having been discovered, both in the 
beds immediately beneath, and in those overlying this siliceous rockf, 
there can be little doubt (especially as they repose upon the rocks of the 
Longmynd, and graduate upwards into the great mass of the Lower 
Silurian Eocks) that the band of the Stiper Stones, with its associated 
underlying black schists, represents, on the whole, the ' Zone Primordiale' 
of Barrande — that is, the Lingula-flags, upper and lower, of North Wales. 
It is well to observe that the finely micaceous sandy shale or schist 
which underlies the more siliceous portion of the series has a great 
similarity in composition to the beds above these quartz -rocks. In short, 
the whole of the beds are so knit together, and pass so imperceptibly 
* See 1 Silurian System,' pp. 284-5, for further search, I reexamined the northern portion of my 
details respecting the structure and relations of old ground, accompanied by Mr. Gibbs, and had. 
these rocks. the satisfaction to detect some of these Lingula?, 
t These fossils, and many others in the beds as well as siliceous flagstones with Scolithi, in an 
immediately overlying the" Stiper Stones, were integral part of the Stiper Stones at Eskridge, 
found by Mr. Gibbs, the able collector of the near Lord's Hill. 
Geological Survey, in August 18.36. During this 
Fossils (4). Annelide-burrows in the Stiper Stones. 
a. 
The burrows have 
two apertures, and 
are connected below 
by a loop-like tube, 
as at a. 
