A HISTORY OF NORTHAMPTONSHIRE 



where numerous small nodules occur, called 

 ' Race,' a system of screening has to be adopted, 

 the clay is pressed through perforated plates, and 

 the small nodules are left on the top. This is 

 practised at Corby Brickworks. Of course iron 

 pyrites is also bad in a clay, the bricks made 

 from such a material are likely to effloresce much 

 with wetting and drying, owing to the crystal- 

 lization of sulphates of iron, calcium, and mag- 

 nesium. The Upper Lias clays formerly worked 

 at Grafton Regis and Paulerspury are particularly 

 liable to this defect. 



At some of the brickyards, tiles, drain-pipes, 

 flower-pots, etc., are made. 



The Lower Estuarine Beds are mostly sands, 

 but here and there, are sufficiently argillaceous 

 to be classed as clays, and at Cottingham and 

 Deene have been used for brickmaking. 



The Upper Estuarine Beds, constituting the 

 base of the Great Oolite series, are really very 

 good clays for brickmaking, and it is rather 

 singular that they are not more often used. 

 The best red facing bricks used in Northampton 

 are made from this clay at Hopping Hill, be- 

 tween Northampton and New Duston. The 

 writer does not know of any other brickworks 

 in operation, but such have been at Buttocks 

 Booth and Moulton Park, both north-east of 

 Northampton and south of Moulton ; between 

 Stanion and Brigstock, Great Oakley, and Wood- 

 newton. Fire-bricks and tile-ware of peculiar 

 hardness and soundness are made from this clay, 

 to the north of Stamford, just outside the county.' 



The Great Oolite clay has been used for 

 brick-making at Bedford Purlieus and New Eng- 

 land, near Peterborough. It is somewhat bitu- 

 minous near to Peterborough. 



The Oxford clay, and particularly the lower 

 portion known as the Kellaways Beds, has been 

 worked a little in Northamptonshire, at Raunds, 

 near Brigstock, Benefield, Southwick, Oundle 

 and elsewhere. 



As to pottery clays, both of the Estuarine 

 Beds, the upper and the lower, have been used 

 for pottery and terra-cotta, where they approxi- 

 mate to one another in composition by the 

 lower becoming argillaceous or the upper sili- 

 ceous, such changes being likely to occur in 

 Estuarine deposits. 



The Roman pottery found at Castor (Duro- 

 brivae), near to Peterborough, was probably made 

 from the Estuarine clays in Normangate Field there. 



Prof. Judd states ' that west of Burghley Park 

 the Lower Estuarine clays were worked up into 

 terra cotta. The clay was i to 4 ft. thick, 

 of a pale blue colour, and somewhat sandy, and 

 according to Mr. Lumby, the then proprietor, 

 it is composed of almost pure silicate of alumina, 

 with a little free sand in very fine grains. This 

 admixture of the clay with fine sand is said to 



' Judd, Geol. of Rutland, etc. 189. 

 ' Geol. of Rutland, 103, 165. 



greatly improve the quality. Mixed with a 

 very small quantity of the white clay from Poole, 

 in Dorsetshire, these Lower Estuarine clays make 

 an excellent cream-coloured terra-cotta. 



The white clays at the base of the Upper 

 Estuarine series at Wakerley constitute an ex- 

 cellent fire-clay, and are used for terra-cotta. 

 They contain a rather small amount of alumina, 

 about 15 per cent., much finely divided quartz, 

 and a fairly large amount of carbonate of lime. 

 Presumably the carbonate of lime combines with 

 the silica in burning. 



LIME 



The chief rock burned for lime in Northamp- 

 tonshire is the Great Oolite limestone, but the 

 marlstone rock-bed, calcareous beds of the 

 Northampton sand, Lincolnshire limestone, and 

 Cornbrash are all used on occasion, so that lime 

 can generally be procured within a few miles of 

 any place in the county. The Marlstone rock- 

 bed is only occasionally fit for lime-burning, and 

 then as a rule only for agricultural purposes ; but 

 the phosphates in it are valuable. The calcareous 

 beds of the Northampton Sand have been used 

 sometimes, but are not a success, as there is 

 a likelihood of much slag being formed. The 

 Cornbrash, too, has only been used for lime-burn- 

 ing, as far as the writer knows, about Peter- 

 borough. 



The more compact limestones give the 

 strongest limes for building purposes, as they are 

 more argillaceous, and so actually form cements. 

 The less compact and purer limestones are, of 

 course, more suited for agricultural purposes. 



Marl has been much used for applying to the 

 land since Saxon times, and no doubt many of 

 the old depressions indicating the sites of ancient 

 excavations were marl-pits. 



Lime Earth is a name given to a cream- 

 coloured argillaceous bed occurring in the Great 

 Oolite limestone series at Oundle that was some- 

 times used for mortar without burning.' A white 

 gritty earth was once obtained at the Clipston 

 stone-pit, which was used to make a kind of 

 plaster by simply mixing with water without 

 previous burning.'' 



CEMENT 



The great cement works of the district, where 

 they use the limestones of the Lower Lias, are a 

 little outside the borders of the county ; but in 

 recent years ' Portland Cement * has been manu- 

 factured at Irthlingborough by Messrs. Dunmore, 

 Limited, who have been good enough to furnish 

 some particulars of their process and analyses of the 

 material. 



' S. Sharp, Quart. Joum. Geol. Soe. xxii, 280. 



* J. Woodward, Nat. Hut. Foil. Eng. (1729), pt. i, 7. 



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