INDUSTRIES 



The Portland cement is made from Great 

 Oolite limestone and Upper Lias clay. Both 

 materials are dried, the stone is crushed to pieces 

 about f in. to i in. cubes ; and they are then 

 mixed in approximately the proportions of five 

 parts of limestone and one part clay, and ground 

 together to a fine powder. This powder, then 

 called raw meal, is damped, pressed into bricks, 

 and the latter burned in ordinary baffle kilns to 

 the point of vitrification. The clinker, which is 

 black and very hard, is then finely ground, and 

 is the Portland cement of commerce. 



Comparative Analyses of Materials and Results 



The insoluble siliceous matter of the clay con- 

 sists of : — 



ROAD METAL 



Probably every one of the hard beds of the 

 Jurassic rocks in Northamptonshire has been used 

 for road metal somewhere, but the chief have 

 been the Marlstone rock-bed, the pendle beds and 

 shatter-stone, or rubble waste of stone quarries 

 in the Northampton sand, Lincolnshire Oolite 

 waste and rag. Great Oolite limestone, and Corn- 

 brash, and so quarries for this purpose have been 

 very numerous, one in nearly every parish — the 

 parish stone-pit ; but since the displacement of 

 soft local stone by the granites, syenites, and 

 metamorphic rocks of Leicestershire or other 

 places for the main roads, one is only occasion- 

 ally opened up or worked for the sporadic repair 

 of by-roads. Most of the old quarries worked 

 for this purpose (or building) only are now grassed 

 over. 



SAND AND GRAVEL 



Gravel abounds in Northamptonshire, deposits 

 of pure sand are rarer, but sand can often be ob- 

 tained by screening the gravel, and the best sand 

 is seldom so good that screening can be avoided. 

 The writer has records of upwards of a hundred 

 sand or gravel pits, and the list is certainly not 

 complete, so that a very abbreviated description 

 will have to be given. 



Northampton Sand. — This is mostly not a 

 sand, although much of it in places may be sand- 

 stone. Still, over by far the larger area where 

 the Northampton sand is worked as an ironstone, 

 including all the easterly parts of the county, the 

 oolitic iron-ore is succeeded directly by the 

 white sands of the Lower Estuarine series. These 

 white sands, dug to such a great extent to get at 

 the underlying ironstone, are very little used. 

 They can be and are used to a limited extent for 

 mortar, with or without a coarser, sharper sand, 

 and for mixing with plaster for walls and ceilings, 

 also for scouring purposes. They have been 

 sent away, too, for furnace work, and can be 

 made into glass. They have been worked for 

 some of the local purposes named at Harpole 

 (Sandy Lane), Kingsthorpe, Earls Barton, and 

 elsewhere. 



Preglacial Sands. — The cleanest and best 

 sand in the county is obtained from some pits in 

 the parishes of Courteenhall (often called Wootton 

 Pits) and Milton, though the same beds extend 

 in a comparatively thin band through Rothers- 

 thorpe, Bugbrooke, Nether Heyford, and to the 

 north of Daventry, and have been worked at all 

 the places named.' Not only is this the best 

 building sand, but the best to be obtained for 

 furnace work in the iron industry. 



There are similar sand beds, possibly of the 

 same age, at Badby, south of Daventry, and in 

 the parishes of Moulton and Overstone. 



Glacial Gravels and Sands. — The widely 

 distributed and often thick beds of intermixed 

 gravel and sand resulting from the washing of 

 the first boulder clay that covered Northampton- 

 shire are commonly called mid-glacial gravels, 

 and they occur anywhere — on the tops of hills 

 or in the bottoms of valleys — but attain their 

 greatest development in the western parts of the 

 county (see article. Geology, in vol. i, p. 25). No 

 place is far from some form of these gravels, so 

 that pits may be opened for a particular purpose 

 and closed again, but in some districts they are 

 deficient in sand, and so sand has to be obtained 

 from a distance. The district towards Har- 

 borough is considered to be a bad one in this 

 respect by builders. 



The gravel beds vary greatly in character, 

 sometimes containing considerable numbers of 

 large well-rounded erratics from rocks older tiian 

 those found in the district, including many Bunter 



' F.C.H. Northanls. i, zz et seq. 



305 



39 



