. Bulletin of the Geological Society of America. Geology. 772; T. C. BROW^^-OOI^TES AND OOLITIC ; TEXTUKE some of the iron does occur as the carbonate. In Georgia, pyrite even is present to a certain extent. As already pointed out, McCallie records the fact that in the Georgia ores many of the spherules show green or yellowish green grannies within them. These increase in numbers 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). Thi
. Bulletin of the Geological Society of America. Geology. 772; T. C. BROW^^-OOI^TES AND OOLITIC ; TEXTUKE some of the iron does occur as the carbonate. In Georgia, pyrite even is present to a certain extent. As already pointed out, McCallie records the fact that in the Georgia ores many of the spherules show green or yellowish green grannies within them. These increase in numbers 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 Hematite Pyrite Quartz Figure 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 Both fossils and oolites have been replaced by iron ore and silica which have come from some outside source; but it is believed that this source was within the beds where these ores are now found, and that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
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