398 
SILTJRIA. 
[Chap. XVI. 
(in ascending order) the Upper Devonian of the Rhine and Belgium, and is dis- 
tinguished by a separate colour in the Prussian map *. 
Palceozoic Rocks of Belgium. — The oldest rocks in Belgium are those of the 
1 Systeme Ardoisier ' of Omalius d'Halloy, or ' Terrain Ardennais ' of Dumont, so 
called from the great development of those slaty quartzose masses which rise 
into the lofty and wild hills of the Ardennes f. These rocks, including the local 
divisions or systems of M. Dumont, called Terrains Devillien, Revinnien, and Sal- 
mien, and even the Gedinnien, or base of the 1 Terrain Rhenan' of that author, are 
now considered by M. de Koninck to be of Lower-Silurian age, seeing that they 
contain only a few imperfect traces of fossils, none of which are of Upper-Silurian 
characters, and also that these slates and grits are unconformably surmounted by 
the lowest zone of true Devonian rocks. 
The triple division of the Devonian rocks of the Rhine, proposed in the first 
edition of this work, is found by M. de Koninck to be essentially correct and ap- 
plicable to Belgium, as determined both by superposition and organic remains. 
The lowest beds, consisting of quartzose conglomerates, and exhibiting imperfect 
casts only of Rhynchonella and Orthis allied to species of the earliest Devonian 
age, are followed by schists laden with those fossils which are common in the 
lowest fossiliferous rocks visible on the banks of the Rhine and its tributary 
the Ahr. On this point M. de Koninck agrees with the Prussian geologists 
von Dechen and Ferd. Romer, and with myself, that the so-called Systemes Co- 
blentzien and Ahrien of Dumont are absolutely one and the same deposit. (See 
the Table at the end of the Chapter.) 
Occurring in Brittany and other parts of France, as will presently be shown, 
these beds are represented in North Devon by the rock forming the North Fore- 
land and cliffs of Ilfracombe (p. 272) ; whilst, judging from some of the fossils, 
M. de Koninck thinks, with us in England, that they have also their equivalents 
at Hope's Nose and Meadsfoot near Torquay in South Devon, and at Looe and 
Fowey in Cornwall. 
The same group of fossils has, indeed, a very wide range, and has been recog- 
nized in the Asturias and other parts of Spain, at Constantinople J, and at the 
Cape of Good Hope, if not in Tasmania. This is the zone which is characte- 
rized by the broad- winged Spiriferi Spirifer hystericus and Sp. cultrijugatus, 
and was well termed ' Spiriferen-Sandstein ' by Ferd. Romer. The other 
principal fossils are Orthis striatula, Schloth., 0. Sedgwicki, de Vern., Terebra- 
tula Archiaci, de Vern., Chonetes sarcinulata, Hupsch, Pterinea lineata, Goldf., 
Grammysia Hamiltonensis, de Vern., Homalonotus armatus, Burm., and Pleuro- 
dictyum problematicum, Goldf., &c. M. de Koninck enumerates, in short, 23 
species which are common to Belgium and the Rhine, many of them being also 
known in Devonshire ; whilst not one of them has been detected in an Upper 
Silurian rock in any part of the world. Just as in my own Table, the Wissen- 
bach Slates are placed by M. de Koninck at the summit of this Lower Devonian 
division. 
The Middle Devonian of Belgium, or calcareous centre of the series, is de- 
* The Prussian geologists have even delineated complete his great work on the Bosphorus and 
on their map three divisions in this one group, Asia Minor (Asie Mineure : Pescription physique; 
which in ascending order are: — 1. Flinz; 2. Kra- 4me Partie, Ge'ologie, le Partie, 1867). In look- 
menzel- Stein; 3. verneuilii-Schiefer. ing at the beautiful and instructive geological map 
t In the Prussian geological map these slates of those regions which he has explored during so 
are also grouped as Devonian. many years, I cannot but suggest that many of the 
J The fullest proofs that the oldest fossils dis- schistose and quasi-crystalline rocks which under- 
covered in the environs of Constantinople (first lie the Devonian rocks of Asia Minor will prove 
noticed by Ham ilton and Strickland) are of Lower- to be of Silurian age. At the last Meeting of the 
Devonian age (that is, of the ' Systeme Khe"nan ' of British Association at Nottingham it gave me 
Dumont — see his Carte Ge"ologique de l'Europe) sincere satisfaction to dwell upon the high merits 
is to be found in M. de Verneuil's description of of this excellent work, 
the fossils collected by M. P. de Tchihatcheff to 
