l88 NEW YORK STATE MUSEUM 



indicated when the proportions of the various constituents conform 

 to a definite silicate formula. 



If the ore is derived from primary silicate, it is evident that the 

 gray oolite, represented by analyses i and 2, must have escaped the 

 alteration and retained its original composition. This involves a 

 difficulty similar to that met with in the attempt to explain the 

 gray oolite as derived from primary oxide — the fact that both 

 silicate and oxide have been subjected to the same geological con- 

 ditions. If the ore represents altered silicate, why has not the 

 much thinner bed of silicate, just below it, been similarly altered? 

 As a matter of fact, both beds appear to have retained essentially 

 their original condition, with little change, and it is impossible to 

 examine them in the field without concluding that their differences 

 are primary. 



Furthermore, if the ore is derived from silicate, why does it never 

 grade into the unaltered original material ? This happens repeatedly 

 in the European cases, where such an origin for the ores has been 

 maintained, while the Clinton ores never, so far as the writer is 

 aware, grade into unchanged silicate, even under covers exceeding 

 a thousand feet. This is really the serious, not to say fatal, obstacle 

 to the hypothesis of derivation of the ores from silicate. An alter- 

 ation so complete and uniform, extending to such depths, over so 

 great an area, and with such widely varying topography, seems 

 impossible. It is true, McCallie 1 states that, in Georgia, the hard, 

 unleached ores carry 4 per cent of ferrous iron while the soft, leached 

 ores carry only about 0.3 per cent. But while this is the relation 

 that would be expected if ferrous silicate is a general primary con- 

 stituent of the ores, no proof is afforded that this silicate was ever 

 the only, or the dominant, iron mineral. For were this the case, 

 there would certainly be parts of the formation, under heavy cover, 

 not reached by the oxidizing solutions where the entire bed would 

 consist of silicate. 



The nearest approach to this that the writer has seen is the bed 

 of gray oolite described above, and the complete preservation of 

 the chamosite in this, with no special protective conditions, 

 strengthens the conclusion that the same mineral would some- 

 times hava remained intact in the ore beds, had it ever formed 

 a chief constituent of the latter. 



If more positive evidence were needed upon this question, it 



1 McCallie, S. W., Fossil Iron Ores of Georgia. Geol. Survey of Georgia, 

 Bui. 17, p. 180, 1908. 



