24 On the Materials ufed 



tion of coaks is at all times neceffary to correct the bad ef-, 



fects which thefe ores, efpecially the former, would other- 



ways produce in the blaft- furnace, though ufed in very fmall 



quantities. 



Thofe iron-ftones with which Britain fo much abounds, 

 and which are now univcrfally ufed for the production of 

 caft-iron with pit-coal, are commonly found in horizontal 

 ftrata, fubject to the fame acclivity and declivity with the other 

 ftratified fubftances under the furface; their inclination 

 from the horizon varying according to the nature of the 

 ground, and the difpofition of the imbedding and incumbent 

 ftrata. Such variety is exhibited, that ftrata of iron-ftone are 

 found defcending i yard in 24, 1 in 13, I in 8, and fome- 

 times 1 in 4. Let AB (Plate I. Fig. 7.) reprefent aline 

 drawn parallel to the horizon, and CD a ftratum of iron- 

 ftone. Suppofe the horizontal line continued for 24 yards : 

 at that diftance the iron-ftone will be found to have de- 

 fcended one yard of perpendicular meafure, at the termina- 

 tion of the lines AB, AD; and if the fame line is fuppofed 

 to meafure 4 or 8 yards, it will reprefent thofe ilrata that are 

 arranged at a more difadvantageous declivity. From this it 

 is obvious, that where the acclivity or declivity of the metals 

 is fmall, the mod extenfive and regular fields of iron-fione 

 are to be found, and vice verfa where the metals lay more 

 on edge. 



Iron-ftones are generally found imbedded in fchiftous clay 

 more or lefs compact, but which moulders away when ex- 

 pofed to air. They afiumetwo different forms : regular con- 

 nected ftrata called bands, and ftrata of detached ftone found 

 in diftindt maffis, from the fize of the fmalleft bullet to the 

 weight of feveral hundred pounds. Thofe of the fmall and^ 

 middling fizes, and which generally wear a flat ovular form, 

 are called ball-ftones : thofe of greater weights are by the 

 workmen denominated Junkers. 



Both thefe fpecics of iron-ftone frequently accompany coal 

 and limeftone. In the former cafe they are commonly in- 

 cumbent, and found almoft in immediate contact with the 



coal : 



