THE CARBONIFEROUS SYSTEM. 



695 



Projection of Millstone Grit. 



coal-measures ; and though thin seams of coal occur in the mountain limestone, the work- 

 able and useful article is only met with in the upper part of the carboniferous system. 

 The argillaceous, or clay-ironstone, is of a grey, brown, or bluish-grey colour, and is 

 scarcely to be discriminated from any ordinary stone except by its greater weight. There 

 are in general several detached strata of it in the same tract of country, each varying in 

 thickness from half an inch to upwards of a foot, and presenting some differences of 

 chemical composition. It occurs also in the form of nodules imbedded in strata of clay or 

 shale, having an oval or conical shape, and composing continuous bands like the flints in 

 chalk. These nodules differ greatly in size, from that of a bean to several feet in diameter, 

 and in weight from an ounce to upwards of a ton. They are often aggregations around 

 shells, or fern branches. To separate the metal from the other ingredients which 

 enter into the composition of the ironstone, coal and limestone are essential ; and 

 it has been properly remarked to be one of the beneficent arrangements of Providence in 

 distributing the rude materials of the earth, that iron, the most useful of all metals, so 

 indispensable to all the arts which bring comfort to man, should be found in immediate 

 connection with the fuel required to melt the ore, and with the limestone, which sub- 

 jects the argillaceous matter in it. by itself infusible, to the action of fire. 



The existence of the iron manufacture in any locality is thus determined by the 

 readiness with which the ironstone as well as the fuel and limestone necessary for its 

 reduction can be procured, and by the facilities afforded in the district for the trans- 

 port of the heavy products to the best markets. The forest of Dean was one of the 

 earliest seats of the manufacture, wood being used as fuel ; but apprehending a scarcity 

 of timber for ship-building, its further employment was restricted by several acts of Queen 

 Elizabeth* Various unsuccessful attempts were soon afterwards made to smelt iron with 

 pit-coal, one of which is detailed in a curious volume entitled Metallum Martis, by 

 Dudley, the founder of the noble family of Dudley and Ward, published in the reign of 

 Charles II* He made the experiment himself, and states : " The author erected a new 

 large furnace on purpose, twenty-seten feet square, all of stone, for his new invention, at 

 a place called Hagcobridge, in the parish of Sedgeley and county of Stafford ; the bellows 

 of which furnace were larger than ordinary bellows are ; in which work he made seiiP.n 

 tons of iron per week, the greatest quantity of pit-coal iron that ever yet was made in 



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