IRON FROM THE OOLITES. 433 



In Lincolnshire iron ore is worked in the Lower Lias, on a lower 

 horizon than the Cleveland ironstone. The mining district lies be- 

 tween the Trent, Humber, and Ancholrne. The ore is sometimes 27 

 feet thick. It is spread about the village of Scunthorpe. The yield 

 is 27 or 28 per cent, of metal. Another band known as the Pecten 

 ironstone is about 4 feet thick, and occurs in the Middle Lias. 



In North Lincolnshire, Frodingham is the centre of the iron 

 district. The ironstone is covered with drift sand. 



In Oxfordshire the Marlstone has been worked for iron ore at 

 Fawler, Aynho, and near Banbury ami Woodstock. The ore is especi- 

 ally developed in the valley of the Cher well. It varies from 10 to 15 

 feet in thickness, and abounds in the Khynclionella tetrahedra. It is 

 often dark olive green, and yields about 32 per cent of metal. 



Above the Upper Lias is the magnetic ironstone known as the 

 Dogger bed. In the Kosedale Abbey mines the band is 20 feet 

 thick, and probably corresponds to the Northampton sand. This ore 

 contains about 65 per cent, of oxide of iron, equal to 45 per cent, of 

 metal * 



Iron Ores from the Oolites. 



The Iron Ore of the Northampton Sand. The Eomans worked 

 the Northampton sand of the Inferior Oolite near Oundle, and the 

 Norman castle of Rockingham is said to have been built for the pro- 

 tection of the iron furnaces of Kockingham Forest. The works, long 

 discontinued, were resumed about 1860. The ore at the surface is 

 hydrated peroxide of iron, but when quarried at some depth, each 

 block has a nucleus of compact impure carbonate of iron, blue or grey, 

 while deeper still the entire mass is carbonate of iron. This mineral 

 replaces the carbonate of lime of fossils, though the greater part of 

 the ore is free from fossils. The ore occurs in lenticular patches 

 at Holt, Desbro, and near Stamford. Sometimes it forms the whole 

 thickness of the formation, sometimes it is entirely absent. It con- 

 tains grains of quartz, which in some beds are invested with hydrated 

 peroxide of iron. Certain beds have the whole mass made up of 

 oolitic grains -J^ to yj^ inch in diameter. On analysis the ores give 

 about 30 to 75 per cent, of sesquioxide of iron, or 60 to 80 per cent, 

 of carbonate. 2 



Beds of ironstone from 4 to 18 feet thick or more occur in North- 

 amptonshire, while at Cogenhoe and Woodford the thickness is 20 feet. 

 The stone at Cogenhoe yields 42 per cent, of metallic iron. At Gay- 

 ton near Blisworth the ironstone is 10 to 14 feet ; at Easton, Neston, 

 near Towcester, from 6 inches to 3 feet ; near Northampton, 1 2 to 

 14 feet ; at Daston, near Northampton, 16 feet. It is largely worked at 

 "Wellingborough, where it is upwards of 1 2 feet thick ; and here the 

 ore yields 53 per cent, of metallic iron. 



1 Meade, " Coal and Iron Industries," p. 368. 



2 Judd, Mem. Geol. Surv., " Geology of Rutland." 

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