40 J. D. Whitney on the Ores of Iron in the Azoic System. 



Grellivara, in Sweden, has a length of three or four miles, and a 

 width of not less than a mile and a half. Of course such a mass 

 of ore, without limit in depth, might be worked on the most en- 

 larged scale for any length of time without fear of exhaustion. 

 The same may be said of some of the iron knobs and ridges of 

 Lake Superior and of Missouri. They form veritable mountains 

 of ore, and ages must elapse before their dimensions will have 

 been perceptibly diminished. This is not necessarily the case 

 with all the localities of ore of these districts. Indeed, in 

 Northern New York and in Scandinavia, although there are 

 accumulations of iron which may be measured by hundreds of 

 feet, or even by miles, yet those which are best known and most 

 worked are of much more reasonable dimensions. 



The character of the ores thus occurring is mineralogically 

 peculiar. They consist uniformly of the oxyds, either the mag- 

 netic or the specular. Hydrous ores, carbonates and the like, are 

 altogether wanting, unless it be upon the borders of the ore de- 

 posits, where a secondary metamorphic action between the fer- 

 riferous mass and the adjacent rocks may have taken place. The 

 oxyds found in this geological position are in general remarkably 

 free from all injurious substances, such as sulphur, arsenic, lead, 

 or zinc, and usually the approach to chemical purity in the ores 

 is in proportion to the extent of the mass, the largest deposits 

 being the purest. The principal foreign ingredient mixed with 

 these ores is silica, which is always present, although frequently 

 in minute quantity. Indeed, the analyses of the Lake Superior 

 and Missouri ores show, in some instances, a surprisingly near 

 approach to a state of absolute purity. It would not be difficult 

 in some localities to procure large quantities of an ore not con- 

 taining more than two or three tenths of one per cent of foreign 

 matter, and that exclusively silica. The purity of the ores may 

 be inferred from the high character and value of the iron manu- 

 factured from them when they have been skilfully worked, as, 

 for instance, in Sweden. Some samples of iron manufactured 

 from Lake Superior ore have, when tested, exhibited a degree of 

 tenacity unequaled by that from any other part of the world. 

 The ores of Lake Superior and Missouri are mostly peroxyds ; 

 those of Northern New York almost exclusively magnetic; 

 while in Scandinavia the magnetic and specular ores are both of 

 frequent occurrence. Those of New York, are often coarse- 

 grained and highly crystalline, while the peroxyds of Lake 

 Superior and Missouri are rarely distinctly crystallized, but are 

 very compact. 



The mode of occurrence of these ores in the regions above 

 mentioned is so peculiar, that, from this point of view alone, it is 

 apparent that these deposits should be classed together as distinct 

 from those in the later geological formations. In all the charac- 



