LEAD ALONE. 159 



The ore must have been deposited with the limestone or it must 

 have been introduced since the latter was formed, and by the per- 

 colation of ore-bearing solutions through the rock, with no marked 

 fissure vein development. The first view has been advanced by J. 

 F. Kemp (1887), it being thought that decaying marine vegetation 

 had precipitated the ores from solution in sea-water, as is outlined 

 for another region under Example 24, but this explanation has 

 been practically disproved. W. P. Jenney has considered the ore 

 to have come in ascending solutions through the small fault fis- 

 sures referred to above, and from these to have spread outward,, 

 replacing the limestone (privately communicated). Places where 

 several fissures cross are said to be specially favorable. It is a 

 curious fact, however, that as the ore bodies are followed up to the 

 faults they invariably become lean or run out. Their place of 

 formation has apparently some connection, as recent explorations 

 seem to indicate, with low folds at right angles to the faults. The 

 ore bodies favor the anticlinal bends. 



This whole region of Cambrian and Lower Silurian rocks, over 

 nearly 3000 square miles, contains lead, and within a year or so past 

 some new mines, not yet under way (1892), have been started. 

 These disseminated deposits are in no way to be confused with 

 the mines of the Upper Mississippi in Wisconsin and Iowa. They 

 are now large producers of lead and the only mines worked in the 

 United States for lead alone. The ore affords an average of about 

 eight per cent, galena. Except at Mine La Motte, lead was also 

 obtained at this region, previously to 1865, from small gash veins 

 like those of Example 24, but the workings were never in any de- 

 gree commensurate with the present mines of disseminated ore. 

 The history of Mine La Motte dates back to the early part of the 

 eighteenth century, and'it is said to have furnished lead for bullets 

 used in the Revolution. 1 



2.05.10. The great increase in lead production in the United 

 States came about 1880, with the opening of the Leadville ore 



1 G. C. Broadhead, " The Southeastern Missouri Lead District," M. E., 

 V. 100. Rec. J. R. Gage, " On the Occurrence of Lead Ores in Missouri," 

 M. E., III. 116. Rec. Oeol. Survey of Missouri, 1873-74, pp. 30, 603. J. 

 F. Kemp, "Notes on the Ore Deposits, etc., in Southeastern Missouri," 

 School of Mines Quarterly, October, 1887. Rec. 



Several other papers have been published on the metallurgical treat- 

 ment and methods of ore dressing in the Trans. Inst. of Mining Engineers 

 and the School of Mines Quarterly. 



