HOBBS MINERALOGY OF WISCONSIN. 121 



The smaller specimen of this type is very similar to the 

 one just described, but the basal plane has a smaller de- 

 velopment, and on one individual it hardly appears at 

 all. It is interesting, however, to note that there has been 

 an addition of the yellow green calcite to this plane, so as 

 to extend the surrounding rhombohedral faces and replace 

 the pinacoid in the manner described for the first specimen. 



The stereographic projection (plate 5, fig. 2) represents 

 all the forms observed on the calcites of this region and 

 exhibits their zonal relationships. 



SMITHSONITE FROM MINERAL POINT. 



The mineral smithsonite occurs at Mineral Point in two 

 forms, one a massive, semi-vitreous, white to gray variety, 

 locally called "calamine, " which incrusts much of the cal- 

 cite and blende of the locality, and the other a porous 

 gray to brown variety known as "dry bone," apparently in 

 all cases a replacement pseudomorph after either calcite 

 or blende. The "dry bone" variety is much the more 

 abundant. The more perfect pseudomorphs after calcite 

 are very beautiful and represent the types 3 and 4 described 

 under calcite. As these pseudomorphs are well known and 

 are somewhat widely distributed in cabinets, a full descrip- 

 tion of them here is unnecessary. They have evidently 

 been produced through the action of solutions by a metaso- 

 matic process of alteration, the lime of the calcite being 

 replaced molecule by molecule by zinc. An examination of 

 the wide range of specimens in the University Collection 

 shows, however, that there have generally been several 

 stages in the process. In most cases the first change was 

 an incrusting of the calcite crystals by the compact "cala- 

 mine" variety of smithsonite. As a result of this nearly 

 all the pseudomorphs have an outer shell of compact ma- 

 terial. The second stage of the process consisted in a 

 partial, and in some cases even a complete, solution of the 

 included calcite crystal. This solution if partial, as was 



