IRON ORES. 355 



everybody who has handled the float at a number of separated localities has 

 been led to remark that some of it is very heavy, while other pieces of exactly 

 the same appearance in other places may be of the weight of ordinary rock. 

 This statement is true, except that there is usually a distinction in the ap- 

 pearance of the two qualities which would not escape the attention of a trained 

 metallurgist. The former variety is almost always gray to bluish gray with 

 a sub-metallic lustre, and the latter is never so, although it may be black and 

 glossy, or even show a hackley fracture. Some of this material is also flinty. 



Now, if the prospector will take the pains to note carefully the localities in 

 which the heavy metallic float occurs, he will probably find that it comes 

 from places where the Fernandan magnetites are buried beneath the Cambrian 

 sandstones. A part of the float, and possibly some of the Cambro-Fernandan 

 contact rocks, may be changed magnetite, but when hematite occurs in such 

 situations it is almost certainly a product from the alteration of the under- 

 lying magnetites. Perhaps the largest portion of this kind of material may 

 have been modified since its deposition in its present locus. The facts remain 

 that it is now hematite of much value, and that the distribution is restricted. 

 The bonanzas of this kind seem to occupy zones following approximately the 

 trends of the magnetite belts. 



It is difficult to explain their formations, for they are usually compact like 

 vein stones, and many of them contain Cambrian fossils, although none of 

 the impressions are very large. 

 - These border ores are very valuable, and some of them may come into 

 market eventually. The necessity for stripping them of an increasing thick- 

 ness of the later strata as they are mined farther from the outcrops will re- 

 tard their development somewhat. At present none of the exposures have 

 been marked, and it is uncertain how much reliance ought to be placed as 

 contributions to the future output of the region. They are prooably not 

 very thick themselves, but they may prove invaluable as "indicators" in the 

 search for buried deposits of the Fernandan magnetites. 



(2) THE CONCRETIONABY HEMATITES (SEGREGATIONS). 



Probably the segregated ores have been drawn up from below to some ex- 

 tent. There is an open door here for the student of chemical geology into a 

 study, the threshhold of which I have only been able thus far to cross. As 

 nearly as my observations can be interpreted as yet, the history after the ac- 

 cumulation of the contact hematites of the Cambrian (chiefly or wholly Lower? 

 Potsdam) seems to have been about as follows: 



1. The deposition of sandstones, highly ferruginous. 



2. The segregation of the iron-bearing portion in streaks and veins 

 through the mass of the sandstones, sometimes impoverishing the rock and 



