396 R. M. BAGG FLUORSPAR IN THE ORDOVICIAN OF WISCONSIN 



cubes and pyritohedrons Cover the calcite surface. In some cases these 

 pyrite crystals formed before the calcite was completely solidified, as 

 shown by intergrowths, but as a rule the two layers are quite distinct. 



The third coating of vein matter filling the joint-planes and seams is 

 fluorite, but in some places this seems to cover the blue limestone surface 

 without the two minerals above referred to underneath. Since the pyrite 

 is highly tarnished and iridescent, it shows in places through the fluor- 

 spar. 



Galena occurs in this same zone and appears as a thin coating on the 

 joint surfaces, with here and there a large well defined cube in the solid 

 crystalline dolomite. 



While the fiuorite usually coats the calcite and pyrite, it is also found 

 on some of the galena seams and more rarely on the limestone walls, but 

 in every case it is the last mineral which w^as deposited. This Neenah 

 fluorite does not develop, however, into good crystals, at least so far as 

 observed, but the coating is heavy, the color intensely purple, and there 

 is sufficient present to give a good etching test. The minerals above re- 

 ferred to appear to be confined to the south side of the larger quarry, 

 where they develop in a massive blue limestone 1 foot thick and some 5 

 feet above the bottom workings. 



Underneath the upper massive dolomite strata the beds become shaly 

 and are very rich in bryozoa, brachiopod, and algae remains. When quar- 

 ried these dark blue shales are so soft that they can be broken in the hands 

 and the rock is discarded in crushing. 



The calcite occasionally assumes a beautiful and delicate rose color, and 

 in one geode center of an orthoceras cast the pink lies in a zonal band 

 surrounded by transparent spar, while the outside of the cast showed 

 galena over the argillaceous surface and stained with purple fluorite. 



Origin of the Fluorite 



It is unlikely that the fluorite under discussion could have been derived 

 from igneous rock which lies deeply buried in the Neenah region. Gran- 

 ite is 675 feet below this same formation 16 miles to the southwest at 

 Oshkosh, and as these quarries lie directly along the strike this same 

 granite can not be far from 700 feet deep under Neenah. 



These limestones dip slightly eastward, and from w^ell borings at Ap- 

 ple ton and at Hortonville we have determined this regional dip to be 17 

 feet to the mile. At the Neenah quarries there is a small dome-shaped 

 curvature and the dip is not uniform, but this may not be structural if 

 the strata were laid down on an undulating base. 



