Page:VCH Northamptonshire 1.djvu/50

 A HISTORY OF NORTHAMPTONSHIRE Bradford Clay of south-eastern -England. In Northamptonshire it is a variegated clay — blue, green, yellow, or purplish, and occasionally bitu- minous (Peterborough) — containing, in irregular layers, white, green, septarian, concretionary, calcareous, or ferruginous nodules. Ostrea sub- rugulosa is fairly abundant, and quantitatively may be regarded as a characteristic species of fossil in differentiating this from the beds im- mediately above (see next section). Blisworth, Stowe-Nine-Churches, Thrapstone, Oundle and Wansford are some of the places where it has been well exposed. The Forest Marble Series This set of beds (named from its occurrence at Wychwood Forest in Oxfordshire) is, in north-eastern Northamptonshire, inseparable from the Great Oolite Clay, hence under the latter name is recorded a thickness of 20 feet. South of the Nene valley, at Stowe-Nine-Churches, near Pattishall, Roade, and Quinton, we have, over beds such as are described in the previous section, variegated clays with thin bands of fibrous car- bonate of lime, hard shales, flaggy limestones with abundant interbedded plant remains, and oyster-beds. At Quinton a bed between 3 and 4 feet thick consists almost entirely of Ostrea sowerbyi, with a smaller number of specimens of Modiola hnbricata and IJnkardium varicosum. Both the Great Oolite Clay and the Forest Marble series, although containing only a marine fauna, by their changeable nature, interbedded vegetation, and other characters suggest distinctly shallow water and estuarine conditions, though there was probably a general sinking and consequent levelling up going on, preparatory to the deposition of the thick argillaceous deposits commencing with the Oxford Clay. The Cornbrash The Cornbrash is usually a hard, blue, fossiliferous limestone when encountered under other rocks ; at the surface it weathers to a yellowish or ruddy colour, and forms a rubbly or brashy rock and soil, supposed to be particularly suited to corn, hence the name. Within Northampton- shire it mostly occurs as isolated masses (see map), but no doubt at one time covered the whole county, for it is the most persistent of all the cal- careous strata of the Oolitic period, being met with right across England. It has been found in Northamptonshire as far westward as Stowe-Nine- Churches, let down by a ' fault. '^ The average thickness is about 5 feet, but in the eastern parts of the county (Peterborough, etc.) it reaches to 1 5 feet. The stone is not much used, though some rough walling may be done with it also road mending ; it is also occasionally burnt for lime. Hist. Soc, No. 48, vol. vi. p. 295. 20
 * Beeby Thompson, ' The Oolitic Rocks of Stowe-Nine-Churches,' Journ. North. Nat,