IRON. 61 J 



of occurrence, origin, and metallurgic uses. It will be convenient here to 

 adopt a scheme based upon commercial relations and modes of occurrence, 

 with reference also to the composition, which has much to do with their eco- 

 nomic utilization. Thus we may separately discuss them under the follow- 

 ing heads, viz. : 



1. The Hard (anhydrous) or Belt Ores. 



2. The Sandy or Comminuted Ores. 



3. The Concretionary or Segregated Ores. 



4. The Soft (hydrous) or Vein Ores. 



5. The Titaniferous Ores. 



This grouping has the slight disadvantage of failing to afford a strictly 

 scientific arrangement, and yet the geologic affinities are more close to the 

 economic relations than might be at first sight supposed. There is also a cer- 

 tain fitness in making two broader divisions; the first to include 1, 4, and a 

 part of 5, or those low in silica (below six per cent); the second comprising 

 2, 3, and the remainder of 5, or the siliceous ores. Analyses of all grades 

 are given in Table III. 



I. HARD OR BELT ORES (ANHYDROUS). 



The lines running about northwest by southeast through the space marked 

 " Iron Ore Belt" upon the Economic Map (Plate XXII) represent the courses 

 of what are probably the axes of folds in the Fernandian rocks. At any rate 

 along each of the lines, wherever these rocks outcrop, there are evidences of 

 the existence of more or less valuable, usually workable, deposits of the hard 

 ores, magnetite and hematite. There has been so much disturbance of the 

 strata, and such an amount of igneous action in places, that absolute uniform- 

 ity of exposure or of quality can not be expected. There is, on the contrary, 

 enough variety in the product to make the proper location of mines a matter 

 of some importance. Nevertheless there is far less difference in the character 

 of the ore in each individual line than among the different lines. The mag- 

 netites and hematites are occasionally distinctly separated, but in many ex- 

 posures the two run together, either in separate bands in the same bed or 

 commingled in varying proportions. The general situation, with much de- 

 tailed description, was clearly depicted in my Report for 1889. Some of that 

 material, with important additions, is incorporated in what is given below. 



A. THE MAGNETITES. 



The original magnetites lie in the northwest Archean or Fernandian trend.* 

 They do not appear in their greatest development in all exposures of these 



*North 36° west by south 36° east nearly. 



