REPORT OF THE DIRECTOR I917 1 87 



ferrous silicate that the green oolite contains, but in less amount, 

 the respective quantities being 22.07 P er cen t and 37.23 per cent. 

 While the weak green color of the silicate in the ore is wholly masked 

 by the strong red of the oxide, in thin section the ore is green by 

 transmitted light, though bright red by reflected light. 



In the change from red to green oolite there has been, through 

 the action of percolating solutions, doubtless of a reducing nature, 

 a loss of hematite, to which the red color was due, while the silicate 

 is relatively increased in quantity by this removal, as well as by the 

 elimination of the unusually abundant iron carbonate. The presence 

 of the large amount of the latter in the ore strongly suggests that its 

 formation is the first step in the removal of the oxide, while the 

 marked decrease in total iron in the green oolite as compared with 

 the ore is added evidence of leaching. 



If this interpretation is correct, the silicate of the green oolite is, 

 in part at least, not formed by the alteration of oxide in the red ore, 

 but is simply rendered conspicuous by the removal of the oxide. 

 That, at the same time, some silicate may be formed is evident. 



So far as the typical oolitic ore and the fossil ore, represented 

 by analyses 11 and 12 are concerned, the silicate can be determined 

 only by indirect means, and nothing definite is indicated as to its 

 relation to the oxide. Streaks and blotches of green oolite occur 

 sporadically in the oolitic ore bed and are essentially identical in 

 nature with those just described. As yet nothing similar has been 

 noted in the fossil ores, probably because of merely accidental over- 

 sight. In both varieties of ore the association of silicate and oxide 

 is most intimate and, apparently, constant. 



Thus, it is concluded that the chamosite, or related ferrous silicate, 

 which occurs as a distinct bed associated with the Clinton hematites, 

 as well as the silicate intimately mingled with hematite in the ores 

 themselves, is a primary deposit rather than an alteration of some 

 other iron compound. 



If this conclusion is correct, the intimate and, apparently, constant 

 association of ferrous silicate with the oxide of the ores suggests 

 at once the possible derivation of the Clinton ores from a primary 

 silicate. 



Such an explanation of the ores would account very well for 

 their constant yielding of gelatinous silica when treated with acids, 

 the silica resulting from the decomposition of a residual portion of 

 the silicate that had escaped alteration. This, however, as will be 

 shown later, is not the only possible source of silica, though distinctly 



