542 POPULAR SCIENCE MONTHLY 



by oxidation or by solvents, the quantity, time and temperature may 

 all be sufficient to accomplish great results with more tractable ores, but 

 have practically no effect upon these refractory ones. A good example 

 of this again is found on the Mesabi range where the heat of an erup- 

 tive rock has so altered a portion of the iron formation for many miles 

 that it has resisted surface solution and concentration, and is a worth- 

 less low-grade mixture of rock and magnetic ore still: while away 

 from the influence of the eruptive, have been formed the iron ore de- 

 posits which have given to the iron and steel industry of this country 

 the raw material required to make us preeminent in the markets of 

 the world. 



Eeduced to more simple language and ideas the foregoing remarks 

 amount to a statement that climate, sun, rain, average temperature, 

 topography, depth of soil or surface debris, erosion, glaciation and 

 other common and often unobserved influences and conditions have 

 decided bearing upon the important question of ore formation. 



These are the phases of our modern theory that have received little 

 attention hitherto; and are yet of practical value that can hardly be 

 overestimated. We find few bonanzas of high-grade ore in Siberia, 

 Russia, Alaska, British Columbia, Washington or northern Ontario. 

 Our theory tells us why they are not to be expected, and why such 

 enriched ores as are found seldom extend downward to great depths. 

 We turn to regions of milder climate, less glaciation, gentler topog- 

 raphy, and we find the rocks altered and softened and oxidized to some 

 depth below the surface. We find that the veins wear " iron hats " ; 

 and beneath them we find bonanzas reaching to great depths. We find 

 our best ore shoots on the sunny sides of the mountains, while the 

 veins on the northern shaded sides where the snow lies till mid-summer 

 and the rocks are cold produce no such rich ore. We begin to realize 

 that our theory is based on fact and proved by observation; and that 

 it justifies us in placing confidence in it, and in acting upon it within 

 reasonable limits. And we marvel that facts so simple and of such 

 easy comprehension and yet of such practical value should receive so 

 little attention from the writers on ore deposits. 



