694: GEOLOGY AND TOPOGRAPHY OF THE LEAD REGION. 



bonate of magnesia, in slightly varying but nearly equal proportions. It occurs occas- 

 ionally in small rhombohedral crystals in cavities of the Galena limestone. The best lo- 

 cality for obtaining cabinet specimens is in the railroad cut at Scales Mound. 



Sraithsouite. Often improperly called Calamine. Composition: carbonic acid, 

 85.18; oxide of zinc, 64.81. This mineral, commonly known as Drybone, is one of 

 the two ores of zinc found in the Lead region. It is found most extensively in the cen- 

 tral and northern parts and usually in connection with blende. It crystallizes in 

 rhombohedral forms; such specimens are, however, rare. It usully occurs massive, hav- 

 ing a structure similar to partially decayed bone, from which it derives its common 

 name. 



Pseudomorphs, of Smithsonite, after calcite, are sometimes formed. They occur as 

 rhombohedrons, and in the various irregular shapes in which calcite occurs in the Lead 

 region. Perfect crystals, in which the transformation from calcite to Smithsonite is 

 complete, are very rare. It is much more common to find skeleton crystals, or those 

 which have been formed by the deposition of a smooth, light-colored shell of Smithsonite, 

 about a sixteenth of an inch thick, over all the exposed surface of the calcite, followed 

 by a gradual removal of the crystal contained within the shell. The space within the 

 shell is sometimes partially filled with Smithsonite, and frequently planes are formed 

 within, parallel to the cleavage planes of the original crystal. Pseudomorphs are also 

 found in which the imperfect crystallization of sphalerite is very evident. Smithsonite 

 is also found covering crystals of galenite, which are undecomposed. 



Cerussite. Composition : carbonic acid, 16.5; oxide of lead, 83.5. Cerussite is occasion- 

 ally fonnd in small pieces, but never in sufficient quantities to form an object of mining. 

 It occurs in irregular rounded pieces of a yellowish color, exhibiting no crystalline 

 structure. It has been found near Mineral Point, and in former years quite frequently 

 at the diggings near Blue Mounds. 



Cerussite is found in small, irregular, translucent crystals of a white or light yellow 

 color, in the mine of Messrs. Poad, Barrett & Tredinnick, near Linden. The specimens 

 seen were large, cubic crystals of galenite coated with pyrite, the crystals of cerussite 

 being formed on both of these minerals. The specimens indicate that the crystals of 

 pyrite had been formed, and many of them broken before the formation of the cerussite. 



Hydrozincite. Composition: carbonic acid, 13.6; oxide of zinc, 75.3; water, 

 11 .1. This is a mineral of rare occurrence in the Lead region. It is found at Linden 

 and Mineral Point as a white, finely crystalline, fibrous incrustation on Smithsonite. 



Malachite. Composition: carbonic acid, 19.9; protoxide of copper, 71.9; water, 

 8.2. It is occasionally found in small seams mixed with other ores of copper in tb.e 

 Mineral Point copper mines. Crystals or good cabinet specimens do not occur. 



Aznrite. Composition: carbonic acid, 25.6; protoxide of copper, 69.2; water, 5.2. 

 It occurs similar to malachite, massive and in seams associated with chalcopyrite. The 

 Mineral Point mines afford very beautiful cabinet specimens of small rhombohedral 

 crystals of dark blue color. 



PRESENT CONDITION OF THE MINES IN THE VARIOUS DISTRICTS. 



In this subdivision of the chapter, it is desired to present such information in regard 

 to the individual mines as has been collected during the course of the survey up to the 

 time when it became necessary to submit the manuscript for publication. This infor- 

 mation has in many cases been procured under difficulties; owing sometimes to tem- 

 porary suspension of mining operations, sometimes, but not often, to the reticence of 

 owners, and sometimes to petty and vexatious hindrances which are best understood by 

 those who have ever attempted to collect such information. It has been our aim per- 

 sonally to inspect and visit all the mines of 'any considerable magnitude, or possessing 



