CHAPTER Y. 



LEAD ALONE. 



2.05.01. The deposits of lead are treated in three different 

 classes, according as they produce or have produced lead alone, 

 lead and zinc, or lead and silver. Of late years the lead-silver ores' 

 have been the great source of the metal. Only the southeast 

 Missouri region is of much importance among the others, although 

 considerable lead is also obtained in association with zinc. 



LEAD SERIES. 



Pb. S. 



Galena, PbS 86.6 13.4 



Cerussite, PbCO 3 77.5 



Anglesite, PbSO 4 67.7 



Pyromorphite, Pb 3 P 3 O 8 +l/3Pb.Cl 2 75.36 



Earthy mixtures of these last three and limonite. 



2.05.02. Example 22. Atlantic border. Veins of galena in 

 the Archaean rocks of the States along the Atlantic border ; also 

 others into Paleozoic strata, as described in the sub-examples. 



2.05.03. Example 22a. Veins in gneiss and crystalline lime- 

 stone, sometimes with a barite or calcite gangue. These deposits 

 were vigorously exploited forty years ago or more, but have since 

 been of small importance other than scientific. They may be 

 described best by districts, as they hardly deserve a greater prom- 

 inence. 



2.05.04. (1) St. Lawrence County, New York. Veins with 

 galena in a gangue of calcite in Archaean gneiss. Those near 

 Rossie are perhaps best known, especially for their unusually in- 

 teresting calcite crystals. There are numbers of veins in the dis- 

 trict which are notable in that the galena is without zinc or iron 

 associates. The lead carries a very small amount of silver, not 

 enough to separate. Hornblende and mica schists occur in the 

 same region and the Potsdam sandstone is not far removed. A few 



