Page:VCH Northamptonshire 1.djvu/46

 A HISTORY OF NORTHAMPTONSHIRE an extensive coral reef, which rises above the general surface of the deposits now constituting the ironstone beds under part of North- ampton. The Lower Estuarine Beds consist, usually, of white or light purplish sands, with some argillaceous matter, but the latter may preponderate. A striking characteristic of these beds is the almost universal presence in them of vertical black streaks or even carbonized stems of plants of contemporaneous growth. Two distinct periods of plant growth may be traced over many square miles,' and at places [e.g. Corby), horizontally bedded carbonaceous matter may be detected between the plant beds, indicating contemporaneous denudation in the neighbourhood. The sand as such is used for various purposes ; where more indurated as a building stone (at Kingsthorpe for example), though very little at the present day ; the clay beds for brickmaking (Dene and else- where), and terra-cotta* manufacture (Stamford). Notwithstanding the often very distinctive characters of these beds, it is impossible to regard them otherwise than as the upper part of one series, the Northampton Sand. The Northampton Sand then embraces the three sets of beds just described, and these may quickly pass from one into the other. For in- stance, at Duston, two miles west of Northampton, the ironstone beds are fully 30 feet thick ; at Berry Wood, three-quarters of a mile to the north- west, in the entire thickness of 68 feet of Northampton Sand there is no true ironstone, but only ferruginous rock ; in another three-quarters of a mile in the same direction the whole exposure, some 30 feet, is white, or only slightly ruddy sand ; at New Duston, one and a half miles nearly north of the ironstone workings, under about 4 feet of white sand, are 42 feet of either ruddy building stone, or calcareous rock and slaty beds, with fossiliferous limestones near the base. In a southerly direction the white sands rest directly upon Upper Lias Clay (Grafton Regis and Paulerspury) ; and in a south-easterly direction the series apparently dies out very rapidly and is not to be detected at and beyond Preston Deanery, which latter place is only four and a half miles from Duston. On passing the Ise brook in a north-easterly direction the Northampton Sand maintains a much more equable facies over a con- siderable area. The Estuarine origin of the deposits may be pretty confidently affirmed, judging by their rapid variations in character, both vertically and horizontally ; beds with corals and other marine fossils alternate with ' Beeby Thompson, 'The Oolitic Rocks at Stowe-Nine-Churches,' Journ. North. Nat. Hist. Soc, No. 48, vol. vi. p. 295 ; 'Excursion to Weldon, Dene, and Gretton,' Proc. Geo/. Assoc, vol. xvi. p. 226 (Nov. 1899). pp. 103, 104. 16
 * John W. Judd, ' The Geology of Rutland,' etc., Memoirs of the Geological Survey,