THE IRON-ORE SUPPLIES OF THE WORLD 375 



stories of this sort in reference to China and India are dis- 

 credited in this monograph. But there seems no reason to 

 doubt that as countries now sparsely occupied become better 

 known increased quantities of ore will be found in them. 



As the monograph deals essentially with the quantity of 

 ore, it does not often refer to the manner in which the ores 

 have been formed. In some cases the genesis of an ore must 

 be determined before the amount can be estimated. Iron ores 

 can be classified according to their mode of origin into six 

 main groups. The first, igneous ores due to magmatic * segre- 

 gations in molten rocks, are represented by the titaniferous 

 magnetites such as occur at Taberg in southern Sweden and 

 at Routivaara in Lapland ; but few ores unquestionably of 

 igneous formation are at present of practical value. It is true 

 that this origin is accepted by some leading authorities for 

 the great masses of magnetite in Lapland ; but this view is not 

 yet established and Mr. Lundbohm, the manager of the Kiruna 

 Mines, both in his report in this monograph and in another 

 submitted at the recent meeting of the Geological Congress, 

 represents this question as still unsettled. 



The second group includes ores formed as contact-deposits 

 beside eruptive rocks ; the present tendency is to transfer some 

 ores, such as those of Gora Blagodat in the Urals, from the 

 magmatic to this group. There is also a somewhat uncertain 

 boundary between contact ores and those of the third group, 

 the lodes and masses due to the replacement of other rock 

 by ironstone. They are represented, for example, by the 

 masses of rich kidney iron ore in the Carboniferous limestones 

 of the north of England, which provide the only British 

 supply of Bessemer ore. This group also includes the famous 

 iron mines of southern and central Sweden. 



The ores of sedimentary origin which form the" fourth group 

 include the most widely distributed ores, now of much economic 

 importance. Amongst them are the Carboniferous and Mesozoic 

 ironstones of the British Isles and of Spain, the Clinton ores 

 of the United States and the vast beds of minette in France 

 and Germany. 



The fifth group comprises the banded ironstones and their 



* Magmatic ores are those formed by the concentration in a molten rock of a 

 metalhc constituent that is normally scattered through it into masses sufficiently 

 large and rich to be worked as ore. 



