PRELIMINARY CHAPTER. 19 



rals, in the Galena lead district, is concerned. The injec- 

 tion of melted matter from below into the fissures of the 

 rocks accounts for the origin of many true mineral veins 

 in a satisfactory manner; but in the lead region of the 

 Xorth-west the vast bodies of unfissured sandstones and 

 other mimctallic formations below the lead-bearing rocks, 

 make it almost impossible to trace the lead to this source. 

 Professor WHITNEY, who is perhaps our best authority 

 upon the geology of the lead region and the modes of 

 occurrence of its mineral deposits, in his articles in the 

 Iowa, Illinois, and Wisconsin Geological Reports, has well 

 nigh settled the question in favor of the deposition of the 

 ore in the crevices of the rocks by aqueous solution. He 

 believes that the minerals were held in solution by the 

 waters of the ocean, which deposited the lead-bearing rocks, 

 and afterwards precipitated or deposited in the fissures, 

 and that the development of life in the ocean produced 

 chemical combinations in the sea water, which caused the 

 precipitation of the sulphurets. In this way sulphurets 

 alone were deposited, but the oxydized combinations of the 

 sulphurets would form the few other accidental minerals 

 found among these sulphurets. 



The surface arrangement and systems of parallelism of 

 the veins or lodes of productive mineral is a subject of 

 interest in the mining district. East and west veins usually 

 carry the mineral. Xorth and south veins are unproduc- 

 tive, except in a few instances, where the general rule 

 seems to be reversed. In connection with this, it may be 

 well to remark that Dr. WHITE, the State Geologist of 

 Iowa, has just announced that there is a well marked 

 physical difference between the lead ore of the east and 

 west, and north and south lodes; and also, that they have 

 found in Iowa lead ore with small adhering crystals of 

 native copper. Both these announcements are interesting 

 discoveries. 



Lead occurs in the form of float mineral, sheet mineral, 



