184 Bulletin of Laboratones of Denison U^tiversity. [Voi.xii 



in any single formation in whose residual decay the ores now 

 exist, but was derived from any formations containing this ele- 

 ment, formerly covering the one in which the ores are now 

 found. There is field-evidence in certain areas to support this 

 statement. 



As shown from the general geologic distribution and mode 

 of occurrence of the ores discussed above, the source of the 

 manganese could not have been from rocks underlying those 

 in whose residual decay the ores are now inclosed. 



Microscopic study of a number of thin sections prepared 

 from hand-specimens of the quartzite, collected by the writer 

 from all parts of the quartzite area, failed to disclose any min- 

 eral substance that could be definitely referred to manganese 

 in any mineralogical form. In order to further test the ab- 

 sence or presence of manganese in the quartzite, large frag- 

 ments were chipped from each hand-specimen, mixed and 

 powdered as one sample. From this bulk of powdered quart- 

 zite, a sample was carefully taken and subjected to a chemical 

 analysis, searching particularly for manganese. The analysis 

 showed no manganese (see analysis on page 161), which confirms 

 the microscopic study. It would not be safe to conclude from 

 a single analysis, though made from a sample prepared from 

 hand-specimens of the rock taken over all parts of the area, that 

 manganese was entirely absent from the formation. When 

 added, however, to similar results from microscopic study, the 

 two greatly strengthen such an inference. If these results 

 should later prove conclusive, the source of the manganese in 

 the decay of the quartzite must then have been from once- 

 existing overlying formations, from which, upon weathering, 

 the manganese was concentrated by chemical and physical con- 

 ditions obtaining ; or, else, the manganese now found in the 

 decay of this formation was originally limited to that part of the 

 formation reduced to decay. 



The Paleozoic rocks are bordered on the east and south in 

 Georgia by older crystalline rocks from which the former rocks 

 were largely derived. These crystalline rocks, made up in part 

 of original igneous masses and in part of original sedimentaries, 



