210 IRON-ORE RESERVES. 



On the other hand, it is scarcely safe to predict a lessening rate of 

 increase, for during the past fifty years it has been thought many 

 times that the increase of rate was checked. 



Tornebohm's estimate of the total reserves of iron ores for the 

 United States is ver}^ conservative, and probably should be greatly 

 increased. His estimate is confined to the producing districts and 

 leaves out of account many important extensions of the ore deposits 

 and districts, many known deposits of good size and quality not now 

 mined because of location or other causes, and large reserves of ore 

 which in the United States are regarded as too low grade to be of 

 present conunercial value, but really of a higher grade than ores 

 counted in the English and German reserves. There should also be 

 included the iron-ore resources of Canada and Mexico innnediately 

 adjacent and accessible to the United States, already largely con- 

 trolled by American capital and probably to be used in part in the 

 United States. 



The ultimate iron-ore resources of North America are still far 

 from known, but there may be no harm in reviewing our present 

 imperfect state of knowledge concerning them. 



A great bulk of the known reserves of the United States is in the 

 Lake Superior region. Tcirnebohm assigns a billion tons to the Lake 

 Superior region, and these figures, while probably small, are in accord 

 with many current estimates. In the producing Lake Superior iron dis- 

 tricts exploration has, for the most part, been sufficiently thorough to 

 make it certain that no large increase of reserves is to be expected. In 

 the Mesabi Range, for instance, 30,000 drill holes and pits have been 

 sunk. The Lake Superior iron districts, however, make up but a small 

 proportion of the region tributary to Lake Superior, constituting less 

 than 4 per cent of the land area included in the U. S. Geological 

 Survey's map of the Lake Superior region. In the remaining 96 per 

 cent there are still large possibilities for finding iron ores. The 

 greatest of the ranges was discovered as late as 1891, and within the 

 last four years two entirely new ranges have been found, though 

 neither of them yet of the first importance. The geological conditions 

 are such as to warrant the belief that more may be found. At the 

 present time exploration in areas intervening between the ranges 

 and in outlying areas is being pushed vigorously, showing the faith 

 of iron men in further possibilities in this direction. The most 

 sanguine, however, would scarcely hope to find ores equal in amount 

 to those already known. 



Lake Superior geological conditions are known to extend north- 

 ward and northeastward through Ontario, suggesting an important 

 source of supply here. The present known iron-ore supply of this 



