772 T. C. BEOWX OOIilTES AKD OOLITie j TEXTURE 



some of the iron does occur as the carbonate. In Georgia, pyrite even is 

 present to a certain extent. As already pointed ont. McCallie records 

 the fact that in the Georgia ores many of the spherules show green or 

 yellowish green granules within them. These increase in niunbers as 

 the sections are taken from greater depths, and a diamond drill core from 

 the Birmingham district at a depth of 800 feet from the surface reveals 

 a large amount of this material (called glauconite by McCallie). This 

 suggests that perhaps the reactions outlined by Cayeux for the European 

 oolitic iron ores may all have taken place in the history of the formation 

 of the Clinton ores. The possible replacements in passing from iron 

 carbonate to the minerals now found in the ores are graphically sum- 

 marized in figure 2. Calcium carbonate would first be changed to sider- 



Calcite 

 Siderite 



Hematite Limonite Henatite Pyrite Quartz 



FiGUBE 2. — Graphic Summary of mineralogic Changes in Ores 



Modified from Cayeux. This shows the various mineral changes through which the 

 aragonite oolites may have passed between their original condition and their present 

 condition. 



ite, and then this might give rise to any one of the minerals — red hema- 

 tite, limonite, chlorite (Cayeux = glauconite of McCallie), pyrite, or 

 quartz. 



It is not within the field of the present paper to discuss the origin of 

 the Clinton ores. The writer is convinced that all of the iron now found 

 in the ore beds was probably deposited in them or near them in some 

 form or other, but not as an oxide of oolitic texture. The iron oxide of 

 the oolites is a secondary mineral exactly as the iron oxide of the fossils 

 is a secondary mineral. Both fossils and oolites have been replaced by 

 iron ore and silica which have come from some outside source; but it is 

 believed that this source was within the beds where these ores are now 

 found, and that the replacement was produced by slow movements of 

 ground water. In the discussion of the siliceous oolites it was suggested 

 that the silica probably came from diatoms and sponge spicules. The 

 silica here might have been derived from the same source; but it seems 



