330 
SILUKIA. 
[Chap. XIII. 
demonstrated by Sedgwick *. In the sequel it will be seen how greatly this 
lower member of the Permian group is expanded on the western flank of the 
Pennine chain. 
Professor King, who had long studied the fossils of the calcareous members 
of the group in the county of Durham, placed the detailed component parts 
of the Permian group still more closely in comparison with the corresponding 
beds of Germany. Thus, whilst, with Sedgwick, he considers that the lower 
sandstones of Yorkshire and Durham, whether red, white, or yellow, which lie 
between the Coal and the Magnesian Limestone are the true equivalents of the 
German Koth-liegende, and that the Marl-slate, with its Fishes, stands in the 
place of the Copper-slate of Germany, he also shows that the fossiliferous 
beds f of compact limestone represent the Lower, and the brecciated and concre- 
tionary limestones of Durham the Upper Zechstein of the Germans, with its 
overlying beds of Dolomite, Rauchwacke, and Stinkstein. 
In England there is, perhaps, no other yellow limestone so charged with 
magnesia as to form a true dolomite ; and hence, in the early days of geology, it 
was natural to define this rock as the Magnesian Limestone %, and to associate 
with it certain subordinate strata. But now that yellow magnesian limestones 
are known to occur, on a stupendous scale, in the Lower Silurian rocks of 
North America §, — in both the Devonian and Carboniferous series of Russia, — 
partially even in the Carboniferous Limestone of Derbyshire and Ireland, — 
and whilst the Jurassic masses of the Alps are to a great extent crystalline 
magnesian limestones or dolomites ||, — it became necessary to abandon the term 
1 magnesian,' and to place the English formation under a general name derived 
from a vast region where the position and fossil contents of the group are 
clearly exhibited. 
The Permian deposits, as developed in Russia, and also in Germany and 
England, do not stop, as before said, in the ascending order with the Zechstein. 
They include another overlying red sandstone, which in many parts of Germany, 
as already shown, also constitutes the conformable roof of the Zechstein, and 
contains the plant Calamites arenaceus, Jag., with its Carboniferous aspect. In 
Russia, indeed, some of these overlying red beds are charged, as we have seen, 
with the Shells of the Zechstein and Plants of the Roth-liegende. In general 
language, therefore, the Zechstein of the Continent, and the Magnesian Lime- 
stone of England, may be viewed as the calcareous centre of an arenaceous group, 
or, as before said, a lower ' Trias,' — the upper red marl and sand of Yorkshire, 
described by Sedgwick, being as much a parcel of it as those red sandstones and 
conglomerates, or ' Roth-todt-liegende,' which in Western Europe lie be- 
neath it. 
In some tracts these latter rocks, so diversified elsewhere, are represented by a 
band of siliceous conglomerate, so poor in fossils that, with the New Red and 
Vosges Sandstones, the Zechstein, and Kupfer-Schiefer, they were named 
* See Sedgwick on the Magnesian Limestone, 
Trans. Geol. Soc. Lond. 2nd ser. vol iii. p. 37. 
t See Prof. King's ' Monograph of the Permian 
Fossils of England, published by the Palseonto- 
graphical Society, 1850, in which he describes 217 
species of Shells, Corals, and other animals, many 
of them common to Germany and Russia. 
J I am, however, disposed to think that some 
of the yellow beds of the Carboniferous Limestone 
of the Clee Hills are exceptions (see Sil. Syst. 
p. 119). The dolomitized Carboniferous Lime- 
stone of the south of Ireland, described by Pro- 
fessor E. Harkness (Quart. Journ. Geol. Soc. 
vol. XV. p. 100), is also to be borne in mind. 
§ See Dale Owen's Geology of Wisconsin, Iowa, 
and Minnesota, with a Map, on which vast mag- 
nesian limestones are laid down as the Lower 
Silurian of that author. 1853. 
|| True dolomite, whether crystalline or earthy, 
is known by its containing 45 per cent, of mag- 
nesia. Another proof of the inapplicability of 
mineral terms to designate the age of strata is the 
use of the term ' oolitic ' for rocks which in Eng- 
land have a lithological structure that is scarcely 
ever found in their continental Jurassic equiva- 
lents. ' Magnesian Limestone ' is also merely an 
insular and misleading name. 
