IRON ORES OF THE CLINTON FORMATION 49 



form clay and amounts to some 2 or 3^ as a rule. The lime and 

 magnesia are due to limestone which occurs as a cementing ma- 

 terial or as unreplaced fossil fragments. They are in largest quan- 

 tity in the fossil ores where the carbonates average from 15 to 20^. 

 The oolitic ores carry about 10 or 12;^ of carbonates as a rule. 



Origin of the Clinton ores 



The subject of the derivation of the hematites, which are so con- 

 stant an accompaniment of the Clinton formation, has been re- 

 peatedly discussed in the literature relating to the geology of the 

 different fields. There is more than scientific interest involved in the 

 question, since the mode of origin has a bearing upon the distri- 

 bution of the deposits and its determination is desirable as an aid 

 to exploration. It has become quite evident with the progress of 

 investigations that there is a great degree of uniformity in the 

 character and manner of occurrence of the Clinton ores throughout 

 their extent and that they have been formed in most, if not all, 

 cases under similar conditions. 



Of the many principles that are known to govern the accumula- 

 tion of iron ores in their varied development, it is possible to elimi- 

 nate all but a few as having no conceivable relation to the Clinton 

 hematites. In fact there are but two explanations which have re- 

 ceived the attention of geologists and need to be considered here. 



According to the first view, originally advanced by James Hall 

 in his description of the Clinton formation in western New York, 

 the ores were formed in standing water at the same time as the 

 inclosing beds. Hall further expresses the belief that the source of 

 the iron is to be found in the bodies of iron oxids and pyrite con- 

 tained in the old crystalline rocks. Thermal waters are considered 

 to have been influential in the deposition of the oolitic ore and they 

 may have hastened the decomposition of the pyrite. These con- 

 clusions were generally adopted by the early writers. 



The alternative explanation, proposed by Shaler for the Clinton 

 ores in Kentucky and favored by some geologists for the whole as- 

 semblage of Clinton ores, regards the hematite as a secondary intro- 

 duction after the formation had been upraised above sea level. The 

 ore beds are considered to be replacements of original limestones, 

 effected by the circulation of ground waters which leached the 

 ferruginous constituents from the overlying strata. This theory 

 of replacement has found its principal advocates among geologists 



