Mr. Weaver on the Structure of the South of Ireland, 389 
In the Ardennes, the clay slate tract {terrain ardoisier), re- 
ferred to the Cambrian system, is divided into three stages: 
the lower destitute of fossils; the medial, in which roofing- 
slate abounds, but in which few fossils have hitherto been 
found ; and the upper, more quartzose than slaty, in which 
the vestiges of life begin to acquire greater extension, and in 
which the first indications of limestone appear, the latter 
being generally slaty, containing numerous crinoidal remains, 
and forming beds about a yard in thickness, but never occur- 
ring in mass like the limestone of the anthraciferous tract. 
In this upper stage M. Dumont notices Orthoceratites, Cri- 
7 ioidea,, Pohjparia^ Trilobites,, Strophomena^ &c.; but accord- 
ing to M. d’ Omalius d’ Halloy, the most common fossils which 
it displays are SpirifercE greatly expanded in the direction of 
their breadth, besides species referable to the genera Caly- 
mene, Asaphus, Orthoceras, Hamites^ Leptcena, Strophomena, 
and remains of Crinoidea and Polyparia^, M. d’ Halloy 
admits that the fossils of this clayslate tract have not been 
determined with sufficient exactness. Yet as far as developed 
by himself and M. Dumont, can it be safely maintained that 
a precise analogy has been established between them and 
those found in the Cambrian system ? 
The clayslate tract, thus referred to the Cambrian system, 
passes in its upper stage by insensible gradations into the 
anthraciferous tract t? both on the north-western and south- 
eastern sides of the Ardennes; in the former direction in Bel- 
gium, and in the latter in the Eifel. 
In the anthraciferous tract, the lower quartzo-schistoiis 
system, referred partly to the Llandeilo and Caradoc forma- 
tion and partly to the Wenlock shale, is divided by M. Du- 
mont into three stages : the lower, which contains no lime- 
stone nor fossils, or at least the latter, are extremely rare ; the 
medial, in which the remains of organized bodies are also 
very seldom exhibited ; and the upper, distinguished by the 
abundance and variety of its Shells and Polyparia from all 
other portions of the anthraciferous tract. In the upper 
stage, nodules or beds of fossiliferous limestone are often con- 
Bruxelles, 1832, a work respecting which I agree with M. Beyrich, that it 
does not appear to have drawn as much attention as it deserves. See the 
same author also on the Ardennes, Belgium, &c,, in the Bulletin de V Acade- 
mie Royale dcs Sciences d B^nuellcs, Novembev 1836 and November 1837. 
* JElemens de Geologie, troisieme edition, 1839, pp. 476, 477. 
t Terrain unthraxifere — this term, introduced in 1808, by M. d’Halloy, 
is admitted by the author not to be good, since anthracite is found in other 
groups, and it does not occur in all the systems which compose the tract 
designated as anthraciferous by himself and M. Dumont . — Elemens de Geo- 
looie^ third edition, p. 438. 
