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acuta, Trigonia costata, Pholadomya fidicula, Ceromya Bajociana, Goniomya literata, Perna rugosa, &c.
These slates, according to Prof. Morris, may partly represent the beds which overlie the Dogger in Yorkshire (the Lower Shale and Sandstone).
They are quarried at Collyweston, Wittering, Easton, Deene, and Kirby.
The work of quarrying is carried on only in winter, for, if dried by the summer sun and wind, the rock hardens and will not split. The holes are blocked up in spring, and the quarrymen then employ their time in the preparation of the slate.' The splitting is caused by the presence of organic remains. (Phillips.)
Overlying the Collyweston Slates of Stamford (to quote Prof. Morris) there is a series of cream-coloured marly limestones, as well as oolitic rag-stones of some thickness (about 75 feet), as seen in the quarries near Stamford, where they yield the so-called “Stamford Marble. They occur also at Barnack (Barnack Rag'), Casterton, Geeston, Ketton (freestone ?), Collyweston and Morcot, Denton, Ponton, Corby, Weldon, &c., where they furnish valuable building-stone.
The beds contain, among Mollusca, Nerinæa cingenda, Ceromya Bajociana, Pholadomya fidicula, Pinna cuneata, Mytilus Sowerbyanus, Astarte elegans, Pecten pumilus, Terebratula submaxillata, &c.; also the Plants Pecopteris, Pterophyllum, and Palæozamia.
These, together with the Collyweston Slates, are placed on the horizon of the upper part of the Inferior Oolite by
i The Barnack Rag is said to have been quarried by the Romans, and the quarries exhausted four hundred years ago. (Sharp.)
9 The Ketton Stone was used in the construction of Peterborough and Ely Cathedrals.
Mr. Judd and Mr. Sharp. This position of the Lincolnshire limestone was first binted at by the Rev. P. B. Brodie and Dr. Lycett.
In Lincolnshire (whence the name) the colitic limestones which constitute the formation attain a thickness of about 200 feet: they thin out near Kettering. At Stamford the thickness is about 80 feet.
The beds are largely worked at Haydor and in the Railway-cutting near Grantham; also at Ancaster.
In the north-western part of Lincolnshire the Rev. J. E. Cross divides the beds as follows:
Lincolnshire Limestone, 36 feet.
Mr. Judd considers that the Lincolnshire Limestone was deposited under moderately deep sea-water conditions, but there are evidences in its lower portion of littoral accumulations. (See p. 172.)
The soil is light and not very productive. The beds, besides being largely used for building-purposes, are burnt for lime.
At Oundle and Higham Ferrers the Northampton Sand is directly overlaid by the Upper Estuarine Series (base of Great Oolite).
The term Fuller's Earth is applied to a thick deposit of blue and yellow clay, divided near the middle, in some localities, by beds of rubbly limestone, called Fuller's Earth Rock. It is characterized by the presence here and there of beds of blue and yellow Fuller's Earth, a sandy clay, which is described by Mr. Bristow as usually of a greenish-brown or greenish-grey colour, sometimes blue.
It is opaque, soft, dull, with a greasy feel, and an earthy fracture. It yields to the nail, and affords a shining streak. It scarcely adheres to the tongue; becomes translucent when placed in water, and falls into a pulpy impalpable powder, without forming a paste with it. The blue Fuller's Earth is frequently of as good a quality as the yellow, for particular purposes, as in fulling coarse cloths, but the yellow is usually esteemed the better.
The general thickness of the veins is from 18 inches to 3 feet. If good, a vein 18 inches in thickness could be worked with profit, but not if of less thickness. Sometimes the vein stops suddenly ; at others it gradually thins out.
Shafts were formerly sunk in the Fuller's Earth south of Bath to a depth of 20 or 30 feet, with levels. It was then much used in fulling at the cloth mills at Bradford-on-Avon, Frome, and in Gloucestershire. It is now, however, rarely if ever worked in the district.
The total thickness of the Fuller's Earth in Somersetshire is from 120 to 150 feet. Nodules of indurated marl sometimes occur in the lower beds.
The Fuller's Earth is largely developed in Dorsetshire (400 feet), but entirely disappears when traced beyond Gloucestershire ; it does not extend beyond Burford on the borders of Oxfordshire. In Gloucestershire it has a thickness of 128 feet at Wotton Underedge, 70 feet at Stroud and Sapperton Tunnel, and occurs as a thin band at Cheltenham. The upper layers are frequently interstratified with beds similar to Great Oolite. (See fig. 15, p. 176.)
Amongst the fossils of the Fuller's Earth may be mentioned Ostrea acuminata, O. rugulosa, Avicula echinata, Pecten vagans, P. lens, Pholadomya truncata, Goniomya literata, Homomya Vezelayi, Isocardia concentrica, Ceromya plicata, Terebratula globata, T. perovalis, T. ornithocephala, and Rhynchonella media (varians).
Mr. R. Tate has estimated the number of species at 93; he regards the deposit as the uppermost zone of the Inferior Oolite.
The Fuller's Earth throws out copious springs, and causes numerous slips on the declivities of the hills around Bath.
Stonesfield Slate. The Stonesfield Slate comprises shelly oolites, gritty limestones, and laminated calcareous sandstones or flags, which, splitting readily along the planes of bedding, produce the so-called slates of Stonesfield. In some places the Stonesfield Slate passes into an oolitic freestone, as near Burford and Windrush. False-bedding is often met with.
The formation is rich in fossil Plants, Corals, Echinoderms, Molluscs, Fishes, Reptiles, and Mammals.
The Mammals include the Amphitherium, Phascolotherium, and Stereognathus; the Reptiles include Megalosaurus, Teleosaurus, and Testudo; the Fishes include Pholidophorus, Lepidotus, Pycnodus, Ganodus, Hybodus, Nemacanthus, Ceratodus, &c. Amongst the Mollusca are Rhynchonella concinna, Trigonia impressa, Gervillia acuta, Ostrea acuminata, &c. The plant-remains include Algæ, Ferns, Cycads, and Conifers.
The flaggy beds are quarried in the Evenlode Valley, at Sarsden, Woodstock, on Sevenhampton Common, Eyeford, &c.; and the freestone beds at Burford and Windrush. Thus, as Mr. Hull remarks, in some places the beds yield slates' for roofing-purposes, in others blocks of stone for building:
The deposit worked for slates is sometimes only a foot in thickness, but it generally consists of two fissile beds of a buff-coloured or grey oolitic limestone called pendle, each about two feet thick, separated by a bed of loose calcareosiliceous sandstone called race, about the same thickness. Concretions are frequent in the latter, and are called whimstones or pot-lids ; they are partially oolitic, sometimes blue in the centre, and vary from six inches to two feet in diameter; their form is generally that of a flattened sphere; they do not break concentrically, but into parallel planes ; and they often contain shells. The pendle, after being quarried, is suffered to lie exposed to the action of a winter's frosts, and the blocks being then struck on their edge with a mallet, freely separate into slates sufficiently thin to afford a light material for roofing. The quarries are principally situated in the valley immediately to the south of Stonesfield village, which branches off eastwards from that of the Evenlode. The mode of working is by driving horizontal galleries about six feet high into the side of the hill, and then extracting the two strata of pendle laterally, piling up the refuse masses of the intermediate bed of race, so as to support the roof: deep perpendicular shafts communicate with these galleries. These workings bave been carried on from remote times to a considerable extent, so that both sides of the valley are completely honey-combed by them. Beautiful plumose stalactites are often found in the fissures of the rock, and are called by the workmen, from an obvious though coarse analogy, tallow. (Conybeare and Phillips.)
Upper Estuarine Series.
Above the Lincolnshire Oolite is a series of blue and grey laminated marls, clays, and shales, 15 to 30 feet in thickness, containing wood and other plant remains, and species of marine and freshwater mollusca. This has been termed by Mr. Judd the Upper Estuarine series. At the base is a ferruginous band rich in fossils.
Mr. Sharp observes that the Upper and Lower Estuarine series occur together in vertical juxtaposition throughout a