328 
SILUEIA. 
[Chap. XIII. 
is a dull-red sandstone *, lying far above all those strata in which traces of 
coal have been found. This red rock gradually assumes a mottled yellow and 
red colour, whilst, in ascending, the yellow colour exclusively prevails in the 
escarpment on the right bank of the river, where a soft yellow sandstone, about 
100 feet thick, and in parts quarried as a freestone, forms the natural and con- 
formable support of the mass of magnesian limestone, the structure of which has 
been well exposed by the cutting of a railroad. These red and yellow sand- 
stones, absolutely dovetailed into each other by mineral characters, exhibit fea- 
tures which are not seen in the underlying Carboniferous rocks, and particularly 
in containing many laminae of false-bedding ; whilst their upper and harder 
courses, gradually becoming slightly calcareous, pass up into the thin flaglike 
strata constituting the base of the Magnesian Limestone : both rocks partake of 
the same flexures. The yellow sandstone with white incoherent beds, and an 
overlying marly flagstone, are traceable at intervals through the county of 
Durham, along the foot of the escarpment of the Magnesian Limestone by 
Sherburn and Ferry Hill, and have been traversed by numerous shafts of the 
more recently made coal-pits. 
In numerous places the limestone is united to the sandstone by means of a 
flaglike marlstone, called Marl-slate by Sedgwick, who has shown it to be the 
equivalent of the Kupfer-Schiefer of Germany ; it contains Lingula Credneri, 
Gein., and fossil Fishes of the genera Paige oniscus, Pygopterus, Coelacanthus, 
Acrolepis, and Platysomus, with Plant-remains (Ullmannia). 
The overlying yellow magnesian limestone is most fully exhibited in the bold 
line of coast-cliff extending from Sunderland to Hartlepool, where its litholo- 
gical varieties and peculiarities, including large round concretions and beds of 
flexible sandstone, were completely described by Sedgwick f. In its range south- 
wards through Yorkshire, this rock is characterized by Axinus obscurus, and, 
though lost for a certain distance under younger deposits some miles to the south 
of the Tees, becomes again an important formation between Doncaster and 
Nottingham. Formerly it furnished materials for the construction of the old 
cathedral churches of York, Beverley, and Ripon ; and recently it has afforded 
the chief building-stone for the Houses of Parliament. The accuracy of the 
sections described by Professor Sedgwick so many years ago, in showing the 
relations of this limestone to the sandstone beneath it, and to certain red and 
occasionally sandy strata above it, as exposed in the southern parts of Yorkshire, 
has been demonstrated by the cutting of the railroad from Bradford to Doncaster. 
In that traverse, the observer, who proceeds from west to east, no sooner leaves 
the coal-field than he passes by, 1st, a thin band of lower red sandstone ; 
* English geologists will perceive that my views t The reader who desires to become acquainted 
respecting the underlying red and yellow sand- with the details of the structure and contents of 
stone, passing up conformably into the Magnesian the Magnesian Limestone and associated strata 
Limestone, are not in accordance with those pro- should consult the following works : — Sedgwick, 
posed by Mr. E. Howse (A.nn. Nat. Hist. 2 ser. Trans. Geol. Soc. 2nd ser. vol. iii. p. 37; King, 
vol. xix. p. 36), in which he unites these sand- Monograph Perm. Foss., 1850, and Ann. Nat. 
stones with the Carboniferous series. I do not Hist. 2nd ser. vol. xvii. ; Howse, ibid. vol. xix. ; 
admit that the occurrence of a few Plants said to Binney, Mem. Lit. & Phil. Soc. Manchester, vol. 
be of Carboniferous species in the underlying xii. and vol. xiv; Kirkby, Quart. Journ. Greol. 
red sandstone at Tynemouth affectsmy conclu- Soc. vol. xvii. & vol. xx. ; Tyneside Nat.-Club 
sions as to the true base of the Permian. In Transactions, 1866, &c. The six subdivisions, in 
visiting both banks of the Wear near Clacks- ascending order, of Marl-slate, Compact Lime- 
heugh, accompanied by Mr. Talbot Aveline, we stone, Magnesian Conglomerate, Shell-limestone, 
saw proofs of such a gradual passage of the red Botryoidal Limestone, and Upper Yellow Lime- 
sandstone into the yellow sandstone, and of the stone, given by Mr. Howse and repeated by Mr. 
latter into the magnesian limestone, that I neces- Davidson as the details of the Permian group 
sarily group them according to the classification (Palseontograph. Soc. Monograph, 1856), are here 
of Professor Sedgwick. I am bound, however, to omitted. They are, in fact, merely local subdivi- 
say that the memoir of Mr. Howse displays talent sions of the Magnesian Limestone of Durham, 
and assiduity, and must be considered a valuable and altogether form the calcareous or central part 
contribution to the history of the Permian rocks only of the natural group defined as Permian in 
and fossils. Eussia and Germany by myself and associates. 
