Dr. F. H. Hatcli — Iron-ores of the United Kingdom. 393 



The Marlstone of South Lincolnshire, Leicestershire, and Oxford- 

 shire is on the whole a "limey" ironstone, and is often self-fluxing. 

 In places, however, where the surface waters have leached out 

 the lime, it is siliceous. Its phosphorus-content averages 0*25 ; 

 sulphur, (W. 



The following are average analyses of the limey and siliceous 

 varieties respectively: — 



It will be seen that chemically the change from the limey to the 

 siliceous type, which is bi'ought about by weathering, consists of 

 a loss of lime and carbon dioxide and an increase of all the other 

 constituents — iron, silica, alumina, and moisture. Physically, the 

 change is from a compact bluish - green ironstone, consisting of 

 carbonate of iron and lime, to a porous brown hydrated oxide of iron 

 or limonite. In the quarries the horizontal lime of demarkation 

 between the two varieties is often clearly discernible. "Where, 

 however, the "cover" consists of clay, shale, or other impermeable 

 material of sufficient thickness to hinder the downward percolation 

 of the surface water, hydration and oxidation of the ironstone are 

 prevented, and the green limey variety in that case extends right up 

 to the junction of the ironstone with the cover. 



Before charging into the blast-furnaces, the ironstone of all the 

 districts is usually calcined, although a certain proportion is fed raw 

 into the furnaces. The object of calcining is, in the case of the 

 oxidized stone, to eliminate the water. In the case of the green 

 carbonate stone, the effect is to drive off the carbon dioxide and 

 convert the iron to peroxide. The loss on calcination is roughly 

 25 per cent of the weight. Consequently, calcination at the point of 

 origin saves railway carriage. It has the disadvantage, however, on 

 the one hand, that exposure to the weather may result in the calcined 

 material absorbing a considerable amount of water on its journey to 

 the furnaces, and, on the other, that the handling and transportation 

 of the dry material may engender a considerable quantity of dust, 

 which is objectionable to the men engaged in its discharging, and 

 tends to choke up the furnaces. 



