596 Iron. 



It is not unlikely, also, that these subterranean waters 

 must often have been warm, seeing that they some- 

 times lay deep in the interior of the earth, and came 

 within the influence of internal heat, whatever may 

 be its origin. If so, it is all the more likely that the 

 ores which we meet with in these cracks or lodes were 

 formed by infiltration of solutions, followed by deposi- 

 tion ; for strings of copper, lead, and tin, for example, 

 occur in the mass, just in the same way that we find 

 mixed with them strings of carbonate of lime or quartz. 

 This being so, then, just as the lime and silica may have 

 been derived from the percolation of water through the 

 rocks that form the country on each side of the lode, so 

 the metalliferous deposits seem to have been derived 

 from metalliferous matter minutely disseminated 

 through the neighbouring formations. We are, how- 

 ever, still in the dark as to many of the conditions under 

 which the process was carried on. 



Ores of iron are common in lodes, and in hollows or 

 pockets, both in the limestones of the Devonian and 

 Carboniferous periods. In North Lancashire, at and 

 near Ulverstone, rich deposits of haematite lie among 

 the joints and other fissures of the limestone, and often 

 fill large ramifying caverns deep underground. A vast 

 trade has sprung up in the district in consequence of 

 these discoveries within the last twenty-five years. 



In the Coal-measures, however, we have our greatest 

 sources of mineral wealth, because they have been the 

 means of developing other kinds of industry besides 

 that which immediately arises from the discovery of 

 the minerals which the Coal-measures contain. In the 

 great coalfields of this formation occur all the beds of 

 coal worth working in Britain. In the South Wales 

 coalfield there are more than 100 beds of coal, about 



