IRON ORES. 347 



investigation can be made of the causes which have produced these ores. 

 There are important differences in the geology of the two regions here men- 

 tioned, and it is too early now to decide whether the deposition of manga- 

 nese minerals has been affected thereby, or whether the similarities may not 

 outweigh the divergences. It is interesting to note that the Fernandan and 

 Silurian strikes occur in both places. 



Manganese as an ingredient of limonitic ores is not uncommon in veins of 

 different ages, but perhaps most frequently in those following the more an- 

 cient trends. A good illustration of this is given in Table IV, No. 5. In 

 some cases particular streaks are strongly enough charged with the oxide to 

 entitle them to be called ferruginous-manganese ores, rather than manganif- 

 erous iron ores. But it is doubtful whether any of these accumulations are 

 important enough to cut any figure in the industrial development of the 

 region. 



IV. THE IRON ORES. 



In a region of very rugged topography, much broken by faults and deeply 

 eroded, it is not reasonable to expect that exposures of any one group of 

 rocks will occur in all parts alike. It does happen in this case, however, 

 that almost everything within the wide range from Archaean to Recent is 

 somewhere exposed in such manner as to enable its structure to be under- 

 stood. Thus it is that the history of iron deposits in our district has been 

 pretty closely made out, so that the resources of this kind may be estimated 

 with some degree of accurary. 



The three classes of iron ores, viz., the Magnetites, Hematites, and Hydrous 

 Oxides, are all represented, and each has practically a locus, or mode of oc- 

 currence, of its own. It is best to treat these classes separately. 



1. MAGNETITES. 



The Magnetites lie in the northwest Archaean trend. They do not appear 

 in their greatest development in all exposures of these rocks, and it may be 

 doubted whether there is actually a continuous bed, or set of beds, forming 

 a definite horizon in the Fernandan System. Some of the outcrops comport 

 as well or better with the idea that they are "lenses" or "bosses" of ore 

 brought to their present condition by local causes. But in many instances it 

 has been found that, while the large masses may be apparently discontinuous 

 across the region, there is usually an indicator of continuity in the shape of 

 a line of ferruginous soil or other land mark; and when the undecomposed 

 hard ore again presents a topographic outline of its own, it is usually found 

 to possess the same character as its representatives in the same trend. This 

 statement may be verified by any one who will take the trouble to note the 



