66 THE PROSPECTOR'S HANDBOOK. 



Before B.F. it blackens and becomes magnetic. Colours 

 borax green. Dissolves in nitric acid, but, though a car- 

 bonate, does not effervesce much, unless in a powdered 

 state. Heated in a closed tube, often decrepitates, and 

 turns black and magnetic. 



Clay ironstone of the Black Band seam is an impure 

 variety. 



The oxides and carbonates of iron are the principal ores, 

 and their gangues are calcareous, argillaceous, siliceous, or 

 bituminous, their value depending in a certain degree on 

 the associated minerals. Thus: In spathic ores, 5 to 15 

 per cent, of manganese or carbonaceous matter in a clay 

 stone is an advantage ; whereas some iron ores are de 

 creased in worth by being associated with iron pyrites, &c. 



Magnetic iron ore occurs in granite, gneiss, schist rocks, 

 clay slate, and limestone. 



Remarkable deposits of red haematite occur in Carbon- 

 iferous, Cambrian, Silurian, and Devonian rocks. In Cum- 

 berland, North Lancashire, and Wales, veins run north and 

 south in mountain limestone. Brown iron ore deposits 

 occur in Carboniferous Limestone and Lower Coal measures 

 in several places in England and Wales , also in the Lias, 

 Oolite, and Lower Greensand of some places. In Spain 

 brown haematite is found in a cretaceous formation. Spa- 

 thic ores occur in carboniferous rocks, as well as in Devonian 

 and older rocks. Clay ironstone is found in shales and 

 clays of the Coal measures, also in Lias formation. 



The Titaniferous iron ore, sometimes massive, but usually 

 in the form of dark black sand washed down from the 

 rocks in the country around, is very plentiful in some parts 

 of North America, New Zealand, &c., and is often associated 

 with gold, gems, heavy metallic compounds, &c. Unfor- 

 tunately the ore is rather refractory. 



It can be distinguished from specular iron (for which it 

 might be mistaken) by its black streak. 



Lead. 



Lead compounds, if heated with carbonate of soda on 

 charcoal before the blowpipe flame, yield malleable metal, 

 and also yellow oxide of lead incrustation. 



