218 



THE GEOLOGIST. 



try, the Forest of Dean claims to have been among the first localities 

 where the manufacture of that metal was established. And, although 

 it is needless to enter into any elaborate conjectures as to why the dis- 

 trict was originally selected, the circumstance that a most abundant 

 supply existed of wood of the kinds best suited to smelting purposes- 

 such as oak, ash, birch, &c., and the fact that the basset edges of the 

 limestone strata, in which the principal deposits of ore occur, bring the 

 mine measures " to the surface, so as to mix the ore with, and render 

 it conspicuous in, the alluvial soil, must not be overlooked, as these are 

 certainly among the most probable causes that can be imagined. The 

 occurrence of vast heaps of slag and scoriae, often charged with thirty 

 to forty per cent, of partly-reduced metal, seem to show that the earliest 

 smelting operations were in air-bloomeries, which may be briefly de- 

 scribed as low conical furnaces having a small opening near the ground 

 to admit the air, and a larger orifice at the top for the introduction of 

 the ore and fuel, as well as to allow the gases to escape. The practice in 

 these furnaces was to stratify the ore with the charcoal, and to promote 

 a degree of combustion sufficient to eff'ect a gradual de-oxidation of the 

 mineral, which, as the name air-bloomery implies, from no artificial 

 blast being employed, was eftected by selecting for the site of the 

 furnace an elevated or exposed situation, where the winds had their 

 greatest force. This process of reduction, however, must have been 

 most lengthy and tedious, since nothing but a long cementation of the 

 ore with the fuel could have caused the m^etallic particles to unite ; 

 and as, even under most favourable conditions, only imperfect fusion 

 would then be obtained, the elimination of the unreduced portions of the 

 ore was completed mechanically under the hammer. It was these 

 expelled and partly fused particles that formed the greater portion of 

 scorlaceous slags, before mentioned, which have been found in such 

 large quantities, and which, in after times, were destined to form an 

 important source of supply to the blast-furnace properly so-called. It 

 lias been stated by the late Mr. David Mushet that, for nearly two 

 Imndred years, the blast-furnaces in the Forest of Dean used nearly 

 one-half of these slags in a charge since it had been found highly ad- 

 vantageous to mix them with the calcareous ores of the district. In one 

 of the ancient slag-heaps on the Monmouthshire side of the Forest, were 

 found embedded some Eoman coins and the remains of a sacrificial altar, 

 which might, perhaps, enable us to assign a period to the scoria) in 



