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(300 to 2,000 feet).
Shale, with hard thinly-bedded sandstones in places (Yoredale sandstones).
Black shales with thin earthy limestones.
The lowest beds of the Carboniferous series in Northumberland and the Tweed valley have been classed as the Tuedian Group by Mr. G. Tate. They consist of shales, slaty and calcareous sandstones, thin beds of argillaceous limestone, sometimes magnesian, and chert, with remains of plants, but no workable coal. The thickness is about 1,000 feet. The beds contain remains of plants, mollusca, and fish.
In the eastern part of the Eden Basin, resting on the Upper Old Red Sandstone, is a series of shales, impure limestones, calcareous conglomerates, obliquely laminated red sandstones sometimes containing pebbles of quartz and assuming a conglomeratic character, and which pass upwards into the principal mass of the Carboniferous Limestone. This series, lately described by Mr. Goodchild, includes the con
1 The Tuedian Group and the Lower Limestone Shale are homotaxeous with the Calciferous Sandstone group of Scotland.
glomerates of Cross Fell (formerly regarded as Old Red Sandstone), the beds of Ash Fell, Róman Fell, &c., and is probably on the horizon of the Calciferous Sandstone series of Scotland. The thickness of the series is from 800 to 1,000 feet, and its character is changeable.
In the Isle of Man there are certain beds which have been assigned to Old Red Sandstone: they occur north of Peel, and fringe the Carboniferous Limestone north of Castletown. They consist of brecciated conglomerates, and of fine breccia interstratified with red sandstones; they occasionally contain beds of cornstone, and rest unconformably upon the Skiddaw Slates. The beds, however, pass conformably up into the Carboniferous Limestone, and this, in the opinion of Mr. J. Horne, is presumptive proof that they are really of Lower Carboniferous age. He considers that the beds may be cor
related with the Calciferous sandstone series of Scotland.
LOWER LIMESTONE SHALE.
This term is applied in South Wales, Gloucestershire, and Somersetshire, to the beds between the Carboniferous Limestone and Old Red Sandstone.
They consist of clays and shales, sometimes mottled, sandy and micaceous, of various tints, blue, greenish-grey, and brown; with occasional beds of tough bluish limestone, like Carboniferous Limestone, in the upper part, and alternating with beds of sandstone in the lower. In fact they form a passage, between the Old Red Sandstone and the Carboniferous Limestone. Sometimes the shale is very feebly represented, occurring in thin beds rapidly alternating with limestone.
In the gorge of the Avon the aggregate thickness of the beds is stated to be 500 feet; in the Forest of Dean 165 feet; at Caldy Island 400; and on the Mendip Hills 500 feet.
Amongst the fossils are Leptana, Strophomena, Orthis, Chonetes, Crinoidal remains, &c.
At the base of the Lower Limestone Shales of Bristol and the Mendip Hills is found the fish-bed or palate-bed, a conglomeratic bone-bed, so named on account of the number of palatal teeth and spines of fish met with in it. The remains are those of Psammodus, Cochliodus, &c.
Trilobites are met with near the junction with the Old Red Sandstone on the Mendip Hills.
At Farlow in Shropshire, according to Prof. Morris and Mr. G. E. Roberts, the passage beds between the Old Red Sandstone and Carboniferous Limestone, consisting of yellow sandstones and pebble-beds, yield the palatal teeth of fish, and one bed, called the Pterichthys bed,' yields P. macrocephalus.
In the South-West of England and in South Wales, the Lower Limestone Shales form a band of generally depressed land surrounding the Old Red Sandstone, bounded again by an escarpment of the Carboniferous Limestone. Swallow holes frequently mark its junction with the newer rock.
From its appearance, it has sometimes led to fruitless searches for coal.
CARBONIFEROUS OR MOUNTAIN LIMESTONE.
GREAT SCAR (SCAUR) LIMESTONE. (Sedgwick.)
The Carboniferous Limestone is generally a tough bluishgrey crystalline limestone, which emits a sulphurous smell when fractured. It occurs in massive beds, some of which are oolitic in structure. It is frequently traversed by veins of calc-spar, and by strings or nodules and bands of chert. Layers of chert are sometimes met with which merge gradually into the masses of limestone.
The rock is locally much stained by iron-ore.
The beds are fossiliferous, and chiefly of organic origin; but sometimes few traces of organic remains are discernible.
The most abundant are the Corals Lithostrotion (striatum, basaltiforme, Lithodendron, Syringopora reticulata, Lonsdaleia floriformis, Zaphrentis, and Cyathophyllum; Bryozoa, such as Fenestella and Polypora; Crinoids, including Cyathocrinus, Actinocrinus, Platycrinus, &c.; Molluscs, Productus semireticulatus, P. giganteus, Spirifera, Orthis resupinata, Euomphalus, Bellerophon, Orthoceras, Goniatites, Pleurotomaria, &c.; and Trilobites, Phillipsia, Griffithides, &c.
Edward Forbes observed (in 1854) that many circumstances warrant the supposition that the Carboniferous Limestone of most regions was a deposit in shallow water; and a fact in support of this was stated to be the occurrence of traces of colouring on certain shells, or of the patternmarkings derived from the original colouring.1
In the North of England the limestones are generally spoken of as 'Scar Limestones.' In passing through Northumberland (to quote Professor Phillips) they become continually more and more subdivided by interpolations of sandstone, shale, and coal, till on the sea-coast, north of Belford, a part of this series contains no less than 13 bands of limestone (121 feet in total thickness), separated by many times their thickness of sandstone and shale, and under the whole lie workable seams of coal. The character of the surface of all the western and north-western part of Northumberland corresponds to this change of the component strata. Instead of the beautiful green pastures which delight our eyes amidst the calcareous dales of Derbyshire and Yorkshire, wide, heathy, and boggy moorlands overspread the surface of sandstones and shales; and we seem to wander in a region of barren Coal-Measures, rather than on the range of the thickest Carboniferous Limestones.'
1 The results of recent dredgings show that coloration on shells occurs in deep water.
Under Ingleborough there is a nearly undivided calcareous mass, 400 or 500 feet thick; but at Alston Moor there are no less than twenty different limestones, amounting altogether to 470 feet in thickness, obscured by the interposition of no less than 1,686 feet of sedimentary strata. Farther north these mechanical admixtures increase in amount, while the calcareous strata diminish; and at length, in the northern parts of Northumberland, the limestone district has become a valuable coal-field. (Phillips.)
Professor Phillips has given the following estimates of the thickness of the Scar Limestones:
The Limestone series (1,000 to 3,000 feet in thickness) forms a narrow band on the eastern side of the Vale of Eden; and bordering the west side of the vale, it forms a belt around the old slaty region of the Lake District between Orton and Egremont.'
In the southern part of the Lake District may be mentioned the Kendal grey marble; while, near Egremont, the Cleator Limestone is of local repute.
Near the top of the Carboniferous Limestone at Pendle Hill is the Pendleside Limestone (so called by Mr. Tiddeman), which shows a thickness, with interbedded shales, of about 350 feet. Amongst other rocks are the Great Whernside Limestone (1,000 feet), the Melmerby Scar Limestone, the Dufton Scar Limestone, &c.
In the Isle of Man, the Carboniferous Limestone consists of the Poolvash black marble and limestone group (Posidonia schist of Cumming), and of the (lower) Castletown limestone.
1 At Hesket New Market there are grits, limestones, and shales with thin bands of coal.