218 
fHE GEOLOGIST, 
try, the Forest of Dean claims to have beeu 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 i)robablo causes that can be imagined. The 
occurrence of vast heaps of slag and scoriic, often charged with thirty 
to forty per cent, of partly-reduced metal, seem to show that the earliest 
smelting operations were in air-bloomcrlcs, 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 
tliese furnaces was to stratify the ore with the charcoal, and to promote 
a degree of combustion suflicient to efl'ect a gradual de-oxidation of the 
mineral, which, as the name air-bloomcry implies, from no artificial 
blast being employed, was effected 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 metallic 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 
seoriaceous slag^s, before mentioned, whicli have beeu found in such 
large quantities, and which, in after times, were destined to form an 
important source of supplj' to the blast- furnace properly so-called. It 
has been stated by the late Mr. David Mushet that, for nearly two 
hundred 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 Roman coins and the remains of a sacrificial altar, 
wliifh might, perhaps, enable us to assign a period to the scoria in 
