ORIGIN OF THE FLUORITE 397 



At Kaukauna, a few miles farther north, . similar Ordovician strata 

 show small fault-planes, and these are filled with calcite and pyrite, as at 

 Neenah. No snch faulting was observed at Neenah, however, and the 

 vein fillings are not as pronounced as at Kaukauna. 



If the fluorite came from below, we should find it at Kaukauna, where 

 faulting occurs in the same limestone, and it should be distributed in 

 more than one stratum. 



Large and pronounced rhombic jointing at Neenah cut all the upper 

 la3^ers on massive dolomite, but these joints do not extend dov^nward into 

 the bryozoa shales at the base, at least not where at present exposed. 



It seems more probable, therefore, to the writer that this fluorite was 

 syngenetically deposited in very minute quantity with the galena dis- 

 semination from mineralized Ordovician waters, and that later this was 

 precipitated as a thin coating along more open joint-planes and solution 

 chambers in more crystalline dolomite. 



The presence of fluorine is definitely known in existing oceanic waters, 

 and in Ordovician oceans may have been locally present in larger amount, 

 and thus could have been contemporaneously deposited in the dolomite 

 along with galena, iron sulphide, and calcite, whose secondary enrich- 

 ments now fill these openings. 



Since the jointing is very limited vertically and because we find no 

 evidence of faulting at N'eenah, v^e believe the fluorite was precipitated 

 from lateral secretion. It is not impossible, however, that meteoric waters 

 percolating downward in strata now eroded have added some mineral 

 matter in this layer above the more impervious shales. We do not believe 

 that it came from any deep-seated action, as was so often the case in the 

 igneous rocks of the West. 



