376 SCIENCE PROGRESS 



associated ore bodies, which are ores of great importance in 

 the United States and in all the existing fragments of the ancient 

 continent of Gondwanaland. They occur in Brazil, South 

 Africa, India and Australia. Hitherto it has only been in the 

 Lake Superior region of North America that these ores have 

 been of great importance ; they have there furnished the main 

 supply of material to the iron and steel industry of the 

 United States. The iron has been concentrated into huge 

 bodies of ore by water, which has dissolved the metal from 

 the rocks above and deposited it where the descent of the 

 solution has been stopped by some impermeable layer. 



The last group includes the laterites iwhich are so widely 

 spread as superficial deposits in the tropics and sub-tropics. 

 They extend occasionally farther into the temperate regions, 

 occurring, for example, in workable quantities in the north of 

 Ireland. Hitherto these ores have only been mined to supply 

 local demands or for use as iron-bearing fluxes. Many primitive 

 races still obtain their iron from laterite ; the prehistoric smiths 

 of the early iron age were probably mainly dependent on such 

 ore and in the event of a serious rise in the price of iron ore 

 laterite deposits would once again become of great industrial 

 importance. 



The estimates of the iron ore supplies throughout the world 

 included in the various reports have been collected in tables 

 compiled by Mr. Tegengren ; the chief results are shown in 

 the list on the opposite page. 



The total reserves of ore are shown by the following list 

 to be enormous and ample for all probable requirements. The 

 estimates are the best hitherto made but they are inevitably 

 indefinite. More precise estimates would hardly be worth 

 the time and trouble it would cost to procure them. A final 

 determination of the iron ore available is impracticable because 

 there is no fixed test of what is ore, the availability of a material 

 as ore varying with political and commercial changes. The 

 percentage of iron in a material affords no absolute separation 

 between iron-bearing rock and iron ore. Thus 60 per cent, of 

 iron in a material may be useless when associated with much 

 titanium, whilst another containing only 20 per cent, of iron 

 may be a valuable ore. Commercial conditions also control 

 the profitable working of ore and therefore affect the estimates 

 hitherto made. 



