REPORT OF THE DIRECTOR I917 185 



The really interesting point brought out by the analysis is the 

 actual presence of a ferrous silicate similar to the chamosite of the 

 gray oolite. Other interpretations of the analysis might be offered, 

 but this one not only fits the individual case but is supported by the 

 evidence of the preceding cases. 



The results from the recalculation of no. 12, shown in no. 12a, 

 are unsatisfactory. This is due, in part, to the fact that the deter- 

 mination of CO 2 is only approximate and, in part, again, to the 

 small amount of silicate present. But, that it actually is present, 

 there can be little doubt. 



This last analysis, taken by itself, would shed little if any light 

 upon the constitution of the ores, but it falls in line with the other 

 analyses and, when all are considered together, while at the same 

 time their geological and mineralogical relations are kept in view, 

 much that is of interest appears. 



As already stated, many specimens of Clinton ore from various 

 localities, have been treated with acid and in every case a residue 

 of gelatinous silica, soluble in alkalies and retaining perfectly the 

 form and structure of the spherules and grains, has been obtained; 

 and the same thing has been noted by several observers in ores of 

 similar character and of various regions and ages. 



The gray oolite, represented by analyses nos. 1 and 2, behaves in 

 precisely the same manner and, in this case, the gelatinous silica is 

 evidently derived from the ferrous silicate chamosite or a related 

 mineral. In spite of some variation in composition, the same con- 

 clusion is justified in the case of the green and red oolites, nos. 9 and 

 10, the latter of which is a low-grade ore. For the two ores, nos. 

 11 and 12, the evidence is not so satisfactory but suggests the 

 presence of a similar silicate. 



Thus the conclusion might seem warranted that, in all cases where 

 iron ores of the Clinton type leave a gelatinous residue on digestion 

 with acids, this residue results from the' decomposition of a ferrous 

 silicate. While this may be too sweeping a conclusion, it is clear 

 that a ferrous silicate is a frequent constituent of such ores and, 

 when present, is the source of the gelatinous residue. 



It is evident that, if the ferrous silicate is so generally present 

 in the Clinton ores, any hypothesis attempting to explain their 

 genesis must take the silicate into account, as has been done in the 

 case of other ores of a more or less similar character. 



Approaching the problem from the side of the silicate, the gray 

 oolite, though leaving much to be determined, presents certain facts 

 which seem to have a very definite bearing upon its origin. 



