394 
SILUKIA. 
[Chap. XVI. 
scribed p. 272, the geologist has really before him the successive representatives 
of the several Rhenish and Belgian deposits. 
The reader who may refer back to the sixth volume of the ' Trans. Geol. Soc. 
Lond.' p. 252, will therefore understand that all the Rhenish ground which is 
described or coloured in the map and sections as 'Upper Silurian ' was soon after- 
wards classed with the Devonian rocks. In their admirable descriptions of the 
Devonian fossils, MM. d'Archiac and de "Verneuil have but to add the one plate 
of the so-called Silurian fossils to their thirteen plates of true Devonian types, 
and all the general features of our labours are in agreement with the latest ob- 
servations. 
In truth, if the field-geologist makes his survey faithfully, and establishes a cor- 
rect order of superposition, his physical facts will eventually be found to coincide 
with the zoological evidence. Of this the Rhenish Provinces and Belgium have 
afforded the best illustrations ; for, notwithstanding the opinion of my distin- 
guished cotemporary, the lamented M. Dumont, who too much undervalued fossil 
evidence, it is essentially the study of organic remains which has led to the clear 
subdivision of the vast mass of older rocks which were there formerly merged 
under the term 'GrauwackeV The authority of M. de Koninck will be cited 
in the sequel in support of views similar to my own. 
Ascending Se?*ies in the Rhenish Provinces and Belgium. — The slaty masses of 
the Ardennes, or the oldest rocks of the region (' le Terrain Ardennais ' of Du- 
mont), may be considered Lower Silurian ; for, though their fossils are very 
rare and obscure, they are unconformably surmounted by the lowest Devo- 
nian strata, thus leaving no place for the Upper Silurian rocks. 
M. Hebert *, indeed, has shown that certain fossils (for the most part very im- 
perfect) of the rocks in which I formerly observed Homalonoti and traces of 
Shells, then thought to be Silurian, are similar to those of Nehou in Normandy, 
and hence that the beds immediately covering the fossil-bearing slates of the 
Ardennes are really the base of all the Devonian rocks. This conclusion is in 
unison with the belief expressed to me by my distinguished friend H. von 
Dechen, so competent a judge of the relative age of all the rock-masses of this 
region, and, as will presently be seen, is amply sustained by M. de Koninck. 
Neither in the gorges of the Rhine between Bingen and the mouth of the 
Lahn, where the rocks have been highly contorted and much subjected to 
slaty cleavage, nor in the quartzose ranges of the Taunus and the Hundsriick, 
has any one been able to detect true Silurian fossils. On the contrary, the 
identification of the limestone of Stromberg on the south edge of the Hunds- 
riick with the Eifel Limestone f, and the discovery by Fridolin Sandberger 
of certain fossils (by no means lowest-Devonian species) along the northern 
edges of the Taunus, have substantiated the views originally embraced by 
Professor Sedgwick and myself. Commencing our inquiry, however, where 
the order of superposition, aided by palaeontology, diffuses a clear light, we find 
in the Rhenish countries the following ascending series of the Devonian rocks 
properly so called : — 
Lower Devonian or ' Spiriferen-Sandsteinj' and Wissenbach Slates, fyc. — Slaty 
schists, with interpolated sandstones and quartzose rocks, with a rare trace of 
impure limestone, rise up in numerous folds from beneath all the adjacent strata 
in the gorge of the Rhine between Coblentz and Caub. This is the ' Aeltere 
Rheinische Grauwacke ' of F. Romer, the ' Spiriferen-Sandstein ' of Sandberger, 
* See Bull. Soc. G-e'ol. de France, deux. se'r. t Ferdinand Ei5mer and Fridolin Sandberger 
•vol. xii. p. 1165. agree in this opinion. 
