14 . [KELLY'S The Forest Marble (with Bradf01'd Clay).-The strata tranquil sea. After the accumuLation of a great thlCkness which own this name occupy a considerable surface area of mud, an elevation of the sea-iioor accompanied by a clear­ in the north and west of Wilt"hire. From Bradford-on­ ing of the waters made the conditions fit for the growth of Avon andCorsham (where they are well exposed in the coral reefs. In the Coral Rag we have a bed of rubbly railway cutting), they run northward to Tetbury, and then oolitic limestone, fnIl of the remains of corals and about 20 turning north-east form a tract some 5 or 6 mile/! wide, on feet thick: it is accompanied by beds of sand and calcareous which stand the villages of Ashley, Crudwell and Kemble. sandstones, termed the Upper and tb.e Lower Calcareous The strata are a variable series of shelly limestones, sands Grit. Near Westburv.a bed of iron-ore (hydrated peroxide) .and clays, about (Fig. 91) 60 feet thick near Tetbury, but has been argely worked; it occupies a narrow strip of thickening as they are followed southwards. NelJ,r Bradford ground running north and south near the railway station, a thick mass of clay, the Bradford o'ay, is locally developed and the bed of ore is from 11 to 14 feet in thickness. In in the lower portion of the Forest Marble. It is a pale grey 1877 there were raised 79,176 tons of iron-ore, valued at ~lay about 40 feet thick, containing a little carbonate of £19,784, but in 1879 the amount had fallen to 47,623 tons, lime and enclosing thin slabs of brownish limestone and valued at £9,525. OSlrea deltoidea is a very common fossil sandstone; a fossil called the Pear Encrinite (Apiocrinites here. At , .many fine corals, snch as Theeos­ rotundus) is abundant iu the Bradfor.d Clay; its fragments milia annularis, are found, mostly on the surface of the are called" coach wheels" by the quarrymen. The large ploughed fields; at Seend the Lower Calcareous Grit is well slabs of coarse limestone furnished by the Forest Marble exposed where the furnace/! for the iron-ore stand. From proper, are, according to Professor Bnckman, " of great this point we can follow the beds ·by Westbrook to Calne, value for forming the sides of piggeries and cattle sheds. and thence by Hillmarton and' ~urton to Highworth. At The smaller pieces broken up form a very durable material the latter place 'the total thickness is about 100 feet, and fine for road-making, and some of the thicker blue-centred slabs sections are exhibited where the beds are quarried for are used for building purposes. As a soil the Forest Marble building stone. Spines and plates of a sea-urchin (fJidaris is usually poor, but capable of great improvement by drain­ florigemma) are very characteristic of the Coral Rag. Physi­ ing and cnItivation." The remains of the oldest known cally this bed forms a ridge or escarpment;-Tu(Ing about 100 British Crab (Palreinachus longipes) were found by Thf1'. feet above the plain of Oxford Clay; bytts aecomposition it WIlliam Bury, in the Forest Marble near Malmesbury. produces a light sandy arable soil. At Calne specimens of The Cornbrash.-This is a rubbly, pale-coloured earthy a new genus of sea-urchin (Pelanechinus) which possessed a J1mesione, about 20 feet thick. We can trace it between flexible test have been found by Mr. Keeping.

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Fig. 91. Quarry at Yatton Keynell, near Corsham, a Forest Marble. Fissile shelly oolite, resting obliquely on the Great Oolite; 4 feet. b Great Ooiite (upper zone). Regularly bedded massive shelly limestone; 7 feet. o Great Oolite (lower zone). Shelly oolite, full of false bedding. The upper part coarse; the lower affording very fine building stone, whioh is followed underground; 16 feet.

"l'rowbridge ~nd , and round Great Chalfield and UPPER OOLITE.-Kimmeridge Clay.-Between , ..Atford; frold Corsham and Chippenham it runs by King- Sedghill, and Knoyle Common, we find a bed of blnish­ ton. Hullavington and Malmesb~ry to Charlton and Pool shaly clay. about 65 feet thick; we can trace it again on the Keynes. At Rodborne it is quarried for rough building north-east, between Westbury Station, Worton, and BnIk­ ~tone. The fossils are numerous, and include Ammonites ington; it is then overlapped and concealed bynewerstrata, Herveyi, Avicula echinata, &c. Numerous villages occnr but we recover it again at Olney Marsh, and find it thickens along the outcrop of the Cornbrash, as it is a water-yielding northward to 500 feet at Swindon, where its outcrop is also >stratum; it furnishes a good corn-growing soil. broad, occupying all the ground between Swindon on the MIDDLE OOLITE.-The Oxford Clay (with KelllAJJay, east; and Wootton Bassett and Stratton St. Margaret's on Rock).-This formation consists of blue c1ay. weathering the west There are large brick-pits in the Kimmeridg€ yellow near the surface, and here attains a thickness of Clay at C:;windon ; here Ammonites bipl:e:c is common in II about 500 feet. Near its base is a fossiliferous bed of bed of llandstone, and limestone nodules occur; OlitrefJ calcareous sandstone called Kelloway or Kellaway's Rock, deltoidea is another common fossil. In these pits in 1874 ...either after the village of the latter name near Chippenham bones of enormous extinct reptiles (Omoliaurus, &c.) werE r(Woodward), or because it occurred in pits belonging to a found, which were extracted and removed with great skill. man named Kelloway (Ramsay). The Oxford Clay extends by Mr. W. Davies, of the Britieh Museum, and have sinCE .from Bradley and Melksham to Christian MaIford; then been described by Professor OWell. between Wootton Bassett and Malmesbury the outcrop is 7 Portland Beds.-Strata of this age are exposed in three .miles in width, and so it continues by Purton Station, separate areas in Wiltshire. At Chilmark and Tisbury, in South Cerney, and Cricklade, towards Lechlade; sections the valley of the Nadder, about 12 miles west of , are exposed in the cuttings of the Great Western Railway, there are large quarries in a siliceous limestone, of which .and in brickyards near M~esbury and at Mine~y station. and Wilton Abbey were bnilt. At The Oxford Clay forms a std!, heavy soil, difficult to culti- Tisbury about 61 feet of stone are seen in the quarries, and JVate and mostly in permanent pasture; the ')ld Forest of the beds here contain beautiful yellow crystals of sulphate Braydon stood on it, and there are still many woods. Of of barytes (sugar-candy stone). A coral (IsastTtEa oblonga) :fossils the large flattish oyster-like shell (GryphaIJ. dila'l.lta) which has been converted into flint and chert, is also plen­ is abundant, ammonites and belemnites are also plentiful. tiful at Tisbury. In the valley east of Worton and south of In making the railway cutting near Christian Malford, Pottern sandy beds of the same age occur. Lastly, in the .about I8.j.o, many fossils were fonnd including some new stone quarries at Swindon we see about 8 feet of yellowish forms of cephalopods. which were described by Mr. Pearce Portland stone, underlaid by sands 25 feet thick; there is under the name of Belemnoteuthis; even the impressions of an outlying mass round t.he village of Bourton. their soft parts were wonderfnIly preserved. Remarkable The Portlandian Beds are a marine ~hallow·water series, .branches of some coniferous trees from the Oxford Clay of indicating an upheaval of the oolitic sea-bottom. ~his locality have been figured by Mr. Carruthers in the Purbeck Beds.-8trata of this age occur at two points 11 Geological Magazine" (vol. vii.); he there remarks that only: at Evias, Chicksgrove, and Chilmark Common (t would be very desirable if foliage or fruit could also be slabs of a. thin compact limestone are raised for tiling; at .found. Swindon we see in the stone quarries about 10 feet of fresh- The Coral Rag.-'fhe thick beds of clay we have just water marls and limestones of Purbeck ag-e, which have jescribed were ,pr('bably deposited in a moderately deeop anl;! J yIelded to the diligent researches of Mr. C. Moore•. of Bath,