118 SEVENTH REPORT—1837. 
ferent specimens from the same bed. I have analyzed above 
thirty specimens at different times, generally selected with some 
care, as the object in view was to determine the average good- 
ness of various beds of this ore, that the smelter might have it 
in his power to choose the best for his purpose. 
In general some notion may be formed of the goodness of the 
ore by taking its specific gravity ; the heaviest samples being 
the best. But this rule is not without exceptions ; the specific 
gravity of some of the best specimens being diminished by an 
admixture of coal. The specific gravity of pure crystallized 
carbonate of iron is 3°829. Now the heaviest iron stone which 
I have met with in the neighbourhood of Glasgow has a specific 
gravity of 3°3801. It contains 83°85 per cent. of carbonate of 
iron. The remaining 16°15 parts consist of carbonate of lime, 
carbonate of magnesia, silica, alumina, and coal. A bed of iron 
stone near Airdrie is known by the name of Mushet’s black 
band, because it was discovered by that gentleman, or at least 
its value was first pointed out by him. It contains 85°44 per 
cent. of carbonate of iron, which exceeds that from Crossbasket 
above stated, yet its specific gravity is only 3:0553. It may be 
worth while to state the composition of this black band, because 
it will show the foreign bodies always present, in greater or 
smaller quantity, in the clay iron stone of this district. 
Carbonate of iron... .. 85°44 
Carbonate ‘of lime 20°. S80 2h. 9h) 594 
Carbonate of magnesia. . . . . 3°71 
Siliea hh" Soa ea ee RUE See 
Aliinainia <P o FW 00.09 ee A (ORGS 
Péroxide'of iron 40H 08 2 ht Ag. + O23 
Coaly' matter’ 200) o.oo. me 0. Sef) 3°03-——100'38 
The quantity of silica and alumina in this particular band is 
unusually small, amounting only to about 2 per cent. In some 
specimens of clay iron stone which I have analyzed the alumina 
and silica amounted to 45 per cent. Mushet’s black band con- 
tains no sensible traces of manganese. But in general that 
metal may be discovered, though never in great quantity, in the 
clay iron stone belonging to the Glasgow coal-field. There is 
a bed of iron stone near Johnston, which contains 84 per cent. 
of carbonate of iron; but its lime and magnesia being very 
small in amount, the silica and alumina together constitute 
12°4 per cent. and the coaly matter 14 per cent. 
The lightest specimen of clay iron stone which I have met 
with in the neighbourhood of Glasgow had a specific gravity of 
2°285 owing to the great quantity of coal, no less than 21°71 
per cent., with which it was mixed, Its constituents were 
