132 BULLETIN OP THE UNIVERSITY OF WISCONSIN. 



fig. 3. An analysis of such crystals on selected material 

 from Galena yielded Mr. R. B. Green the following 



results : 



Calculated. 



PbO ........................... 83.42 83.52 



CO 2 ........................... 16.45 16.48 



99.87 100.00 



The material was specially examined for zinc with nega- 

 tive results. 



SPHALERITE FROM SHULLSBURG, MINERAL POINT, AND 



GALENA. 



Although sphalerite is one of the most common minerals 

 in the crevices of the Galena Limestone, it is usually found 

 in the massive form or in small and imperfect crystals. It 

 usually contains a small amount of iron sulphide, as is indi- 

 cated by its dark color. I recently collected at the Wis- 

 consin Zinc and Lead Company's mine at Shullsburg, some 

 specimens of this mineral on which the crystal forms can 

 be made out. These sphalerite crystals occur in an elon- 

 gated roughly cylindrical cavity, which has been formed by 

 the solution and removal of a fossil, probably an ortho- 

 ceras. The largest crystal is over a centimeter in diame- 

 ter and is a much distorted simple individual on which are 

 found the following forms : 



o, + (111). 



d, ocO (110). 



I_ 3O3 /Q1 



m, + -- (311). 



